Anthocyanin Accumulation and Molecular Analysis of Correlated

Apr 8, 2015 - The Institute of Vegetable Research, Chongqing Academy of Agricultural Sciences, 401329 Chongqing, People,s Republic of China...
0 downloads 0 Views 2MB Size
Subscriber access provided by University of South Dakota

Article

Anthocyanin accumulation and molecular analysis of correlated genes in purple kohlrabi (Brassica oleracea var. gongylodes L.) Yanjie Zhang, Zongli Hu, Mingku Zhu, Zhiguo Zhu, Zhijin Wang, Shibing Tian, and Guoping Chen J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.5b00473 • Publication Date (Web): 08 Apr 2015 Downloaded from http://pubs.acs.org on April 12, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Journal of Agricultural and Food Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 37

Journal of Agricultural and Food Chemistry

Anthocyanin accumulation and molecular analysis of correlated genes in purple kohlrabi (Brassica oleracea var. gongylodes L.) Yanjie Zhang1, Zongli Hu1, Mingku Zhu1, Zhiguo Zhu, Zhijin Wang2, Shibing Tian2, Guoping Chen1* 1

Bioengineering College, Key Laboratory of Biorheological Science and Technology

(Chongqing University), Ministry of Education, Chongqing University, Campus B, Room 515, 174 Shapingba Main Street, Chongqing 400044, People’s Republic of China; 2

The Institute of Vegetable Research,Chongqing Academy of Agricultural Sciences,

401329 Chongqing , People’s Republic of China. * Corresponding author. Guoping Chen, Tel: 00862365112674; Fax: 0086 23 65112674; E-mail: [email protected].

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

1

Abstract: Kohlrabi (Brassica oleracea var. gongylodes L.) is an important dietary

2

vegetable cultivated and consumed widely for the round swollen stem. The purple

3

kohlrabi shows abundant anthocyanin accumulation in the leaf and swollen stem.

4

Here, different kinds of anthocyanins were separated and identified from the purple

5

kohlrabi cultivar (Kolibri) by high-performance liquid chromatography-electrospray

6

ionization tandem mass spectrometry. In order to study the molecular mechanism of

7

anthocyanin biosynthesis in purple kohlrabi, the expression of anthocyanin

8

biosynthetic genes and regulatory genes in the purple kohlrabi and green cultivar

9

(Winner) was examined by quantitative PCR. Compared with the colorless parts in the

10

two cultivars, most of the anthocyanin biosynthetic genes and two transcription

11

factors were drastically up-regulated in the purple tissues. To study the effects light

12

shed on anthocyanin accumulation of kohlrabi, total anthocyanin contents and

13

transcripts of associated genes were analyzed in sprouts of the both cultivars grown

14

under light and dark conditions.

15

Keywords Anthocyanin accumulation, Purple kohlrabi, structural genes,transcription

16

factors, HPLC-ESI-MS/MS, Brassica oleracea var. gongylodes L.

17

ACS Paragon Plus Environment

Page 2 of 37

Page 3 of 37

Journal of Agricultural and Food Chemistry

18

INTRODUCTION

19

Anthocyanins,as an important subclass of flavonoids, is the main water-soluble

20

pigments which are widely distributed among higher plants. The red, blue and purple

21

colors found in plant tissues including flowers, leaves, fruits and roots are always

22

attributed to the accumulation of this kind of vacuole pigments. Apart from the

23

well-known physiological function of serving as pollinator and seed disperser

24

attractant, anthocyanins also play essential roles in protecting plants against the

25

damages from UV radiation, coldness, drought stress and microbial agents(1-5). In

26

addition, most plants synthesize anthocyanins as sunscreen which can absorb UV light

27

and serve as free radical scavengers to cancel out the damaging consequence of

28

irradiation(6). Growing evidences indicate that regular intake of anthocyanins can

29

reduce the risk of suffering from artherosclerosis and related diseases by inhibiting the

30

low-density lipid oxidation(7). Besides, anthocyanins can also provide protection

31

against cancer and other chronic illnesses (8-12). The health-promoting effects of

32

anthocyanins are usually believed to be closely linked with the high antioxidant

33

activities and the capacity of eliminating reactive oxygen species. Recent articles

34

show that this kind of second metabolites is able to modulate signaling pathways in

35

mammalian cell for the explanation of some beneficial biological effects (13, 14). As

36

an important subclass of flavonoids, anthocyanins not only play important roles in the

37

physiological plant processes of coloration and adaption to various environmental

38

conditions, but also act as a health-promoting supplement for human diet.

39

Anthocyanins are synthesized through a branch of phenylrpopanoid pathway and the

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

40

genes that directly participate in the process of anthocyanin accumulation have been

41

well studied in snapdragon (Antirrhinum majus), maize (Zea mays), Arabidopsis

42

(Arabidopsis thaliana), petunia (Petunia hybrida), grape (Vitis vinifera L.) and blood

43

Orange (Citrus sinensis L. Osbeck) in recent years (15-17). The pathway responsible

44

for anthocyanin accumulation is showed in figure 1. The biochemical reaction that

45

cinnamic acid is converted by phenylalanine ammonia-lyase (PAL) from

46

phenylalanine represents the initial step, cinnamate 4-hydroxylase (C4H),

47

4-coumaroyl:CoA-ligase (4CL), chalcone synthase (CHS), chalcone isomerase (CHI),

48

flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR) anthocyanidin

49

synthase (ANS) and flavonoid-5-glucosyltransferase (5-GT) catalyze the sequential

50

reactions with the resulted metabolites as substrates in the following steps (18-20). It

51

is worth to mention that B ring of the dihydrokaempferol (DHK) can be further

52

hydroxylated by flavonoid 3′-hydroxylase (F3′H) to produce dihydroquercetin and

53

leads to the production of the cyanidin-based anthocyanins (21). Colored

54

anthocyanidins are formed as a result of the activity of ANS, but the immediate

55

modification, largely by glycosylation is rather necessary for their stabilization (22,

56

23). Then, these modified anthocyanidins will be transported into vacuolar from

57

cytosol. As a glycosylated form of anthocyanidin, anthocyanins include 400

58

molecules to the least extent and exhibit various colors depending on pH, metal

59

cations, co-pigmentation, and modifications of the backbone (24).

60

Anthocyanins, as the metabolites of the flavonoid pathway, are synthesized under

61

the complicated regulation of diverse regulatory genes mainly at the transcriptional

ACS Paragon Plus Environment

Page 4 of 37

Page 5 of 37

Journal of Agricultural and Food Chemistry

62

level (22, 23, 25). The flavonoid downstream pathway (from F3H to 5GT) of

63

anthocyanin biosynthesis is regulated by several different families of regulatory genes

64

including MYB transcriptional factors, bHLH transcriptional factors and WD40-like

65

proteins (26). By analyzing mutants of Arabidopsis thaliana with abnormal levels of

66

anthocyanins, and protein interaction assays, it has been proved that the transcription

67

of anthocyanin biosynthetic genes is directly regulated by a transcriptional activation

68

MYB-bHLH-WD40 complex (MBW) consist of R2R3 MYB, bHLH and WD40

69

proteins (27-29). Recent studies show that variation in content of anthocyanins or

70

tissue specificity in plants is governed mainly by the activity of the R2R3 MYB

71

transcription factors in the MBW complex (30-36). However, the bHLH proteins

72

always play essential roles in the synergistic regulation of anthocyanin accumulation

73

(29, 37-39). In addition, heterogonous expression of bHLH genes individually really

74

induced visible anthocyanin accumulation in host plant (40-42).

75

As a biennial plant native to northern Europe, kohlrabi (Brassica oleracea var.

76

gongylodes) belongs to the Brassicaceae family and is grown widely for the round

77

swollen stem at the base of the plant. Extensive studies show that Cruciferous

78

vegetables (including kohlrabi) supply human beings with healthy diet for the high

79

levels of carotenoids, ascorbic acid and tocopherols contained in the edible parts (43,

80

44). In addition to the natural antioxidants mentioned above, most of the antioxidative

81

effect associated with food intake is largely due to the presence of phenolic

82

compounds including anthocyanins, flavones, flavonols and so on (45). Compared

83

with the green cultivars of kohlrabi, the purple cultivars which display abundant

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 6 of 37

84

anthocyanin accumulation in the stems and leaves apparently attract more attention

85

from consumers for the brilliant color and high levels of health-promoting ingredients.

86

However, being a nutritionally Brassica vegetable worldwide, the molecular

87

mechanisms underlying the biosynthesis of anthocyanins in purple kohlrabi still

88

remain unknown. In this paper, the components of anthocyanin production in the

89

purple kohlrabi cultivar (Kolibri) were characterized with high-performance liquid

90

chromatography−electrospray

91

(HPLC-ESI-MS/MS). In the next, the transcripts of anthocyanin biosynthetic and

92

regulatory genes were analyzed by quantitative real-time polymerase chain reaction

93

(qRT-PCR) in different tissues of the purple and green cultivars (Kolibri and Winner).

94

Furthermore, the influence of light on the development and anthocyanin accumulation

95

of kohlrabi sprouts at different stages were analyzed. The consistent increase of the

96

anthocyanin biosynthetic genes with regulatory factors indicate that transcriptional

97

activation of BoPAP2 and BoTT8 in a light independent manner mainly account for

98

the up-regulation of anthocyanin structural genes and the onset of anthocyanin

99

accumulation in purple kohlrabi. The results above enhanced our understanding about

100

the mechanisms of anthocyanin biosynthesis in purple kohlrabi at both metabolic and

101

molecular levels.

ionization

tandem

mass

spectrometry

102 103

MATERIALS AND METHODS

104

Chemicals and Solvents. Anthocyanin (cyanidin 3, 5-diglucoside) for external

105

standards was purchased from Phytolab (Germany). High-performance liquid

ACS Paragon Plus Environment

Page 7 of 37

Journal of Agricultural and Food Chemistry

106

chromatography (HPLC)-grade formic acid and methanol (MeOH) were bought from

107

Sigma. All the other solvents were provided from Aldrich (St. Louis, MO).

108

Plant materials and culture conditions. Kohlrabi (Brassica oleracea var.

109

gongylodes L.) seeds of green cultivar (Winner) and purple cultivar (Kolibri) were

110

obtained from Chongqing Academy of Agriculture Sciences. The samples used for

111

HPLC-ESI-MS/MS analysis were collected from the cuticles of swollen stem from

112

the two cultivars of kohlrabi which were grown in a greenhouse with a 16-h

113

photoperiod at 22℃. In addition, the mature leaves and the cuticles and fleshes of

114

swollen stem were used for total anthocyanin and qRT-PCR analysis. The light and

115

darkness treated samples used for total anthocyanin and qRT-PCR analysis were

116

collected from sprouts of green and purple cultivars which were generated by follow

117

procedures. Kohlrabi seeds were surface-sterilized with 70% ethanol for 60 s and

118

2.5% (v/v) bleach solution for 5 min, and rinsed six times in sterile water. These seeds

119

were then placed on half-strength sterilized Murashige−Skoog medium (1/2 MS)

120

solidified with 0.8% agar. The two cultivars were germinated in a growth chamber

121

under light/dark (16/8 h) or dark conditions at 26 ℃ and approximately 60% humidity.

122

Samples were harvested after 3, 6, 9, and 12 days, measured for their length and fresh

123

weight, frozen in liquid nitrogen, and stored at −80 ℃ until other analysis.

124

RNA Extraction and qRT-PCR Analysis. The samples of the two kohlrabi cultivars

125

were grounded into powder in liquid nitrogen. Total RNA was isolated from various

126

tissues for three biological repeats using RNAiso reagent according to the

127

manufacturer’s instruction (Takara, Dalian, PRC). RNA samples (1 µg) were reverse

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 8 of 37

128

transcripted into complementary DNA (cDNA) with an oligo(dT)20 primer and

129

M-MLV

130

manufacturer’s protocol. The synthesized cDNAs were diluted five times in H2O for

131

qRT-PCR analysis. qRT-PCR was carried out using the CFX96TM Real-Time System

132

(C1000 thermal cycler). All reactions were performed using the GoTaq qPCR Master

133

Mix according to the manufacturer’s instructions. Reactions were performed in

134

triplicate using 5 µL of Master Mix, 0.25µM of each primer, 1 µL of diluted cDNA

135

and DNase-free water to a final volume of 10 µL. The PCR amplification was as

136

follows: 1 cycle of 2 min at 95℃, 40 cycles of denaturation for 5 s at 95 ℃, annealing

137

for 20 s at 60℃, and elongation for 15 s at 72℃. Amplification was followed by a

138

melting curve analysis with continual fluorescence data acquisition during the 60 −

139

95℃ melt. Melt curve analysis of qPCR samples revealed that there was only one

140

product for each gene primer reaction. The primers used for qPCR analysis of

141

kohlrabi were designed by Primer Premier 5 and listed in Supplementary Table 1

142

(Supporting Information).

143

specific amplifications. The gene expression was normalized to BoApr as a reference

144

gene for kohlrabi. Values reported here were calculated from three biological repeats

145

for each sample.

146

Anthocyanin

147

extraction of kohlrabi was carried out in the same way as described for radish (46).

148

The extract was filtered through a 0.2 µm PTFE syringe filter. The samples were then

149

analyzed by an Agilent Technologies 1200 Series HPLC (Agilent Technologies, Palo

reverse

transcriptase

Extraction

(Promega,

Madison,

WI)

following

the

The PCR products were sequenced to confirm the

and

HPLC−ESI−MS/MS

ACS Paragon Plus Environment

Analysis.

Anthocyanin

Page 9 of 37

Journal of Agricultural and Food Chemistry

150

Alto, CA), equipped with an Agilent 1200 HPLC variable wavelength detector. The

151

results were analyzed by Agilent 1200 HPLC ChemStation software. The

152

chromatographic separation was performed on a Zorbax Stablebond Analytical

153

SB-C18 column (4.6 mm × 250 mm, 5µm, Agilent Technologies, Rising Sun, MD).

154

The injection sling was 5 µL. Elution was performed using mobile phase A (aqueous

155

2% formic acid solution) and mobile phase B (methanol). The detection was at 520

156

nm, and the column oven temperature was set at 40℃. The flow rate was 0.6 mL/min.

157

The gradient program is described as follows: 0–2 min, 10–20% B; 2–40 min, 20

158

–55% B; 40–41 min, 55–80% B; 41–45 min, 80% B; 45–50 min, 80–10% B;

159

50–55 min, 10% B. Quantification of the different anthocyanins was based on peak

160

areas and calculated as equivalents of the standard compounds. All contents were

161

expressed as milligrams per grams dry weight. Low-resolution electrospray mass

162

spectrometry was performed with a solariX ion trap mass spectrometer (Bruker

163

Daltoniks, Billerica, MA). The experimental conditions were as follows: ESI interface,

164

nebulizer, 50 psi; dry gas, 15.0 psi; dry temperature, 320 °C; MS/MS, scan from m/z

165

200 to 1500; ion trap, scan from m/z 200 to 1500; source accumulation, 50 ms; ion

166

accumulation Time, 300 ms; flight time to acquisition cell, 1 ms; smart parameter

167

setting (SPS), compound stability, 50%; trap drive level, 60%.

168

Total Anthocyanin Analysis. Spectrophotometric differential pH method was used

169

for the total anthocyanin measurement of kohlrabi following the procedure of Yuan et

170

al. with slightly modification (25). The protocols are described as follows. Frozen

171

samples (100 mg) were crushed into powder in liquid nitrogen, and extracted

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

172

separately with 2 mL of pH 1.0 buffer and 2 mL of pH 4.5 buffer. In addition, pH 1.0

173

buffer contains 50 mM KCl and 150 mM HCl, while pH 4.5 buffer contains 400 mM

174

sodium acetate and 240 mM HCl. The mixtures were centrifuged at 14,000g for 15

175

min at 4℃. The supernatants were gathered for measurement of absorbance at 510 nm.

176

The amount of total anthocyanin was calculated according to the equation which

177

follows:

178

Amount (mg g-1 FW) = (A1-A2)×484.8/24.825×dilution factor:

179

The A1 represents the absorbance of supernatants gathered from pH 1.0 buffer

180

solution at 510 nm,while the A2 represents the other. 484.8 represents the molecular

181

mass of cyaniding-3-glucoside chloride, while 24,825 reflects its molar absorptivity at

182

510 nm. The total anthocyanin of sample was analyzed in triplicate.

183

Statistical Analyses. SPSS, version 17.0 (SPSS Inc., Chicago, IL) was used for the

184

data analysis. One-way analysis of variance (ANOVA) followed by pair wise

185

comparisons was performed with posthoc Tukey’s honestly significant different (HSD)

186

test, with significance set at p < 0.05 and p < 0.01.

187 188

RESULTS AND DISCUSSION

189

Phenotypic characterization of Kolibri and Winner.

190

To study the biosynthesis of pigments in kohlrabi, the purple cultivar Kolibri and

191

green cultivar Winner were chosen to study. Visual inspection of the kohlrabi

192

cultivars showed that Kolibri displays more purple pigments than Winner (Figure 2 A

193

and Figure 1 S in the Supporting Information). The pigments extracted from purple

ACS Paragon Plus Environment

Page 10 of 37

Page 11 of 37

Journal of Agricultural and Food Chemistry

194

tissues of Kolibri share the same spectral properties with anthocyanin standards

195

(cyanidin 3, 5-diglucoside) and is conformed as anthocyanins in the following

196

HPLC-ESI-MS/MS analysis (Figure 2 C). Compared with Winner, most of the organs

197

of Kolibri contain high amount of anthocyanins (Figure 2 B). During all the

198

developmental stages of vegetative growth, the Kolibri synthesizes and accumulates

199

anthocyanins constantly (Figure 1 S in the supporting information). Meanwhile, the

200

young sprouts of Winner only show faint-purple color at the very beginning of

201

germination, but turn into green immediately as the elongation of hypocotyls. During

202

the initial weeks of growth, all the leaves of Winner turn into solid green, while those

203

of Kolibri display dark purple pigments in the veins of leaves and pale purple color in

204

the mesophyll tissue (Figure 2 A and Figure 1 S in the supporting information). The

205

purple pigments of Kolibri plants, especially in the round stems, become intense

206

during the development. After 2 months of cultivation, the Winner possesses green

207

swollen stems, while Kolibri displays dark purple pigments at the skin of the swollen

208

stems. The intense accumulation of anthocyanins in the purple cultivar indicates a

209

high ability to synthesize and accumulate anthocyanins. The total anthocyanin content

210

of skin of the purple swollen stem is about 0.63mg per gram in fresh weight, while

211

little is detected in the corresponding tissue of Winner. These results show that the

212

drastic differences in anthocyanin accumulation arise from cultivar and genetic

213

specificity.

214

Identification and quantitative analyses of anthocyanins in purple kohlrabi.

215

A total of 6 major anthocyanins were separated and characterized from the cuticle

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

216

extracts of the purple swollen stem with the method of HPLC-ESI-MS/MS (Figure 2

217

C). In order to verify the identity of anthocyanins in Kolibri, fragmentation patterns of

218

MS/MS (m/z) corresponding to the compounds emerged in HPLC profiles were

219

analyzed according to the information of radical groups reported previously (21).

220

Consequently, 6 new kinds of modified cyanidin were identified as the major

221

anthocyanins in the purple cultivar (Table 1). However, it is strange that pelargonidin

222

based anthocyanins were not detected in the purple kohlrabi. Furthermore, all the

223

anthocyanin modifications in Kolibri were found to be glycosylated cyanidin at the

224

C5 position of anthocyanidins. Meanwhile, acylation at the C3 position of

225

anthocyanidins seems like a common modification in this study.

226

Total anthocyanin content was found to be 3.02 mg/g of dry weight for swollen

227

stem skin of Kolibri with the application of HPLC, while there was no trace amount

228

of anthocyanins detected in the corresponding tissue in Winner (Table 1). The content

229

of anthocyanins in Kolibri is similar to those found in the head tissues of red cabbage

230

reported before (25). Moreover, the anthocyanin, cyanidin 3-(caffeoyl) p-coumaroyl

231

(sinapoyl) diglucoside-5-glucoside, shows the highest level (2.08 mg/g dry weight) in

232

the stem skin of Kolibri (Table 1).

233

Transcriptional analysis of anthocyanin biosynthetic and regulatory genes in the

234

both kohlrabi cultivars.

235

In order to investigate the mechanisms underlying the anthocyanin accumulation in

236

purple kohlrabi, the transcripts of anthocyanin biosynthetic enzymes and regulatory

237

genes were examined in the leaves, skins and flesh of the two cultivars by qPCR. The

ACS Paragon Plus Environment

Page 12 of 37

Page 13 of 37

Journal of Agricultural and Food Chemistry

238

expression of anthocyanin biosynthetic genes BoPAL, BoC4H, BoCHS, BoCHI,

239

RsF3H, BoF3′H, BoDFR, BoANS and Bo5GT are shown in Figure 3. Compared with

240

the pigment less tissues, most of the anthocyanin pathway genes were significantly

241

up-regulated in the purple leaves and stem skins of Kolibri.

242

expression of anthocyanin structural genes from BoF3H was drastically increased in

243

the purple kohlrabi in comparison with the green cultivar. In the cuticles of swollen

244

stem, the purple kohlrabi displayed increased expression of nearly all anthocyanin

245

pathway genes except BoCHI and BoC4H. In consistent with pigment production, the

246

higher folds of expression changes happened in skins of swollen stem, while the lower

247

folds of expression changes happened in leaves. Among the up-regulated genes,

248

BoF3H exhibited the highest folds of increase (1000 folds at least) in both the leaves

249

and skins of swollen stems. As the results showed in figure 2, trace amount of all the

250

anthocyanin structural genes were detected by qPCR in different organs of Winner

251

with the absence of visible anthocyanin production. These results indicate that large

252

amount of transcripts of structural genes is a prerequisite for abundant anthocyanin

253

accumulation. Moreover, the constant up regulation of anthocyanin biosynthetic genes

254

in certain colorful organs and/or tissues rich of anthocyanins was also found in

255

red-fleshed apple, purple eggplant, purple tomato, red pear and pap1-D Arabidopsis

256

(30, 32, 34-36). Collectively, the purple kohlrabi shares similar mechanisms of

257

transcriptional regulation in mediating anthocyanin accumulation with those high

258

anthocyanin content plants mentioned above.

259

In the leaves, the

Here, it is worth discussing the absence of pelargonidin based pigments we have

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

260

referred in the anthocyanin profile analysis of the purple kohlrabi. Firstly, the fact that

261

the biosynthetic pathway for anthocyanin accumulation is intact should be admitted

262

for the apparent anthocyanin accumulation in certain tissues in Kolibri. In addition,

263

the substrate specificity of the BoDFR and BoANS is also relatively broad (47). Then,

264

the question seems to become more confused. However, the higher activity of BoF3′H

265

due to the dramatically increased transcripts in purple kohlrabi might provide a

266

reasonable answer to this question (Figure 3). In the anthocyanin biosynthetic

267

pathway showed in figure 1, most of the dihydrokaempferol are applied to produce

268

dihydroquercetin with two hydroxyl group. Consequently, it is no doubt that most of

269

the final products should be cyanindin based anthocyanins. By the same token, the

270

common glycosylated cyanidin at the C5 position of anthocyanidins in Kolibri might

271

probably due to the increased expression of Bo5GT in purple stem skins.

272

To verify whether any of the regulatory genes controlling the transcription of

273

anthocyanin structural genes were up-regulated in Kolibri, the transcripts of some

274

vital anthocyanin biosynthesis regulatory orthologous genes of Arabidopsis, BoPAP1,

275

BoPAP2, BoMYB113, BoMYB114, BoTT8 and BoTTG1 were examined. In

276

Arabidopsis, four R2R3 MYB genes (AtPAP1, AtPAP2, AtMYB113 and AtMYB114)

277

are known to regulate the biosynthesis of anthocyanins directly, while bHLH protein

278

AtTT8 and AtTTG1 play coordinate roles in the formation of transcriptional regulation

279

complex (MBW) (26). Thence, four MYB genes which shared high similarities with

280

anthocyanin biosynthesis activator of Arabidopsis were cloned from the kohlrabi and

281

designated as BoPAP1, BoPAP2, BoMYB113 and BoMYB114. Similarly, BoTT8 and

ACS Paragon Plus Environment

Page 14 of 37

Page 15 of 37

Journal of Agricultural and Food Chemistry

282

BoTTG1, as the orthologous genes of AtTT8 and AtTTG1 respectively, were also

283

cloned. As the results shown in Fig. 4, BoPAP2 and BoTT8 were the only two

284

regulatory genes greatly up-regulated in the tissues rich of anthocyanins. In the leaves,

285

the expression levels of BoPAP2 and BoTT8 in Kolibri were about 990- and 6.8-folds

286

higher than those in Winner respectively. In the skins of swollen stem, the expression

287

levels of BoPAP2 and BoTT8 in Kolibri were about 452- and 57.7-folds higher than

288

those in the green cultivar respectively.

289

In the process of activating anthocyanin biosynthetic genes, the MYB and bHLH

290

transcription factors make different contribution among plant species. In the

291

anthocyanin biosynthesis regulatory complex of MBW, R2R3 MYB transcription

292

factors regulate anthocyanin biosynthesis specifically (48). However, the functions of

293

bHLH transcription factors and WD proteins are rather pleiotropic (26). In addition,

294

the increased expression of both MYB and bHLH is necessary for transcriptional

295

activation of anthocyanin biosynthetic genes in petunia, cauliflower and Arabidopsis

296

(26, 31, 49). Consequently, the dramatically increase of the pigment production and

297

anthocyanin structural genes in purple kohlrabi should be due to the coordinated

298

transcriptional activation of BoPAP2 and BoTT8.

299

Light sheds evident influence on the growth and anthocyanin accumulation of

300

kohlrabi sprouts.

301

To study the effects of light on development and pigment production of kohlrabi,

302

sprouts of the both cultivars grown under light and dark conditions were used as

303

materials. The length, fresh weight and total pigment contents of sprouts were

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

304

examined every 3 days until 12 days after sowing (DAS). As the results figure 5

305

shows, the treated sprouts of Kolibri and Winner displayed completely different

306

phenotypes in production of anthocyanins. Kolibri showed apparent anthocyann

307

accumulation during all the stages of development, no matter of lightness or darkness.

308

However, the pigment intensity in sprouts of Kolibri cultured in light is higher than

309

that cultured in darkness. This phenomenon suggests that the production of pigments

310

is not totally independent of lightness. On the contrary, only tiny amount of pigments

311

were detected in the sprouts of Winner grown under lightness and the production of

312

pigments is totally dependent on lightness (Figure 5 A and B). Whereas, these two

313

kohlrabi cultivars shared the similar trends of growth (Figure 5 C and D). The length

314

increased with time during the entire process of experiments.

315

in darkness showed much higher speed of elongation than cultured in lightness. The

316

lengths of sprouts grown under the dark condition were 2 folds higher than those

317

under light condition after cultured in medium for 9 days. In addition, the fresh weight

318

cultured for 12 days under dark condition did not enhance evidently in comparison

319

with 9 day old sprouts. That is to say, the maximum biomass for kohlrabi sprouts

320

cultured under darkness reached the top at around 9 days. These results are

321

concordant with the findings of buckwheat sprouts in a previous report (50).

322

Expression profiles of anthocyanin biosynthetic and regulatory genes in sprouts

323

of the two kohlrabi cultivars grown in light and dark conditions.

The sprouts cultured

324

To investigate the molecular mechanism of anthocyanin accumulation under light

325

and dark conditions, the expression profiles of anthocyanin pathway and regulatory

ACS Paragon Plus Environment

Page 16 of 37

Page 17 of 37

Journal of Agricultural and Food Chemistry

326

genes in the four groups of materials gathered at different stages were examined. The

327

expression patterns of BoPAL, BoC4H, BoCHS, BoCHI, BoF3H, BoF3′H, BoDFR,

328

BoANS, and Bo5GT are shown in Figure 6. During the different development stages in

329

the light treated sprouts of Kolibri, all the anthocyanin structural genes exhibited the

330

top expression level at 3 DAS. The expression patterns agree well with the amounts of

331

pigment production in the corresponding tissues (Figure 5 B). Compared with the

332

purple sprouts treated in darkness at 3 DAS, the expression of BoPAL, BoC4H, BoCHI,

333

BoF3H, BoF3′H, BoDFR, BoANS and Bo5GT were all slightly raised in the purple

334

sprouts treated in lightness. In the same development stage, the expression of BoCHS

335

in light treated purple sprouts was significantly higher (8.2 folds) than that of purple

336

sprouts under darkness. These results suggest that the expression of BoCHS in purple

337

kohlrabi sprouts is strictly light dependent. Therefore, it is reasonable that the contents

338

of anthocyanins in light treated Kolibri sprouts are higher than those in dark treated

339

sprouts during all the developmental stages. Combined with expression analysis of

340

anthocyanin biosynthetic genes at other developmental stages in purple sprouts, it can

341

be conclude that light enhances the existing production of anthocyanins by

342

strengthening the expression of structural genes, especially BoCHS, at mRNA level.

343

As we have mentioned that trace amount of anthocyanins was detected in the light

344

treated sprouts of Winner, it is not astonishing that the transcripts of most of

345

anthocyanin pathway genes in the corresponding samples were significant higher than

346

that in dark treated sprouts.

347

Expression profiles of anthocyanin biosynthesis regulatory genes in sprouts of the

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

348

two kohlrabi cultivars grown in light and dark conditions are showed in figure 7. In

349

the light treated sprouts of Kolibri at the stage of 3DAS, the expression levels of

350

BoPAP1, BoPAP2 and BoTT8 were about 11-, 6- and 101- folds higher than those in

351

the light treated green cultivar, respectively. It seems that the anthocyanin structural

352

genes are coordinated regulated by BoPAP1, BoPAP2 and BoTT8 in sprouts of Kolibri

353

under light. Furthermore, BoPAP1 was significantly raised at transcriptional level

354

under light in purple sprouts during all the stages of development and was about 23-

355

folds higher than in the dark treated sprouts at 3 DAS. However, light did not shed

356

significant influence on the transcription of BoPAP2 and BoTT8 in purple sprouts. In

357

conclusion, the anthocyanin accumulation and up-regulation of structural genes in the

358

purple kohlrabi sprouts is mainly due to the transcriptional activation of BoPAP2 and

359

BoTT8. In addition, BoPAP1 is the major regulatory gene responsible for the enhanced

360

production of pigments in light treated sprouts.

361

MYB genes associated with the regulation of anthocyanin accumulation are

362

characterized by a conserved DNA-binding domain including two imperfect repeat

363

(R2R3) with a specific motif for the interaction with bHLH domain of bHLH proteins

364

in plant kingdom. The four MYB genes cloned from kohlrabi exhibited high sequence

365

similarities among each other. The putative proteins contain conserved R2R3 MYB

366

domains and belong to the same subgroup 10 of MYB proteins as described by Allan

367

et al. in anthocyanin production regulation (48). In purple swollen stem of Kolibri, the

368

up-regulation of BoTT8 and BoPAP2 probably account for the accumulation of

369

anthocyanins by transcriptional activating the structural genes. Transcriptional factors

ACS Paragon Plus Environment

Page 18 of 37

Page 19 of 37

Journal of Agricultural and Food Chemistry

370

of MYB or bHLH have been reported to be responsible for pigment production in

371

many plant species. In certain anthocyanin-accumulating plants (such as red-fleshed

372

apple, purple sweet potato, in pap1-D Arabidopsis, and maize), the anthocyanin

373

accumulation has been found to be due to an activation of a MYB transcriptional

374

factor(30, 36, 51-53). On the contrary, white-skinned grape arise from the mutations

375

in a R2R3 MYB protein (54). Besides, heterologous expression of bHLH

376

transcriptional factors alters pigment production in the transgenic tomato (40-42, 55).

377

In the tissues rich of anthocyanins in Kolibri, both BoPAP2 and BoTT8 genes were

378

constitutively up-regulated. In the light treated sprouts of Kolibri, BoPAP1 was

379

up-regulated in large folds. Thence, a model illustrating that the transcriptional

380

regulation complex consist of MYB, bHLH and other proteins (BoTTG1) which

381

regulates anthocyanin accumulation coordinatedly was presented in figure 8. In the

382

model, BoTT8 and BoPAP2 promotes kohlrabi colouration in a light independent

383

manner, while the light induced transcriptioa factor BoPAP1 (indicated in dashed

384

cycle) enhanced the existing production of pigments in the light treated sprouts of

385

Kolibri. In summary, the eye-catching purple kohlrabi not only supply human beings

386

with healthy diet for the high levels of carotenoids, ascorbic acid and tocopherols

387

contained in the edible parts, but also with large amounts of natural antioxidants

388

anthocyanins. The elucidations of anthocyanin accumulation at molecular and

389

metabolic levels in purple kohlrabi provide an important basis for the breeding of new

390

kohlrabi cultivars with more excellent agronomic characters.

391

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

392

Abbreviation used

393

PAL, phenylalanine ammonia lyase; C4H, cinnamate 4-hydroxylase; 4CL,

394

4-coumarateCoA ligase; CHS, chalcone synthase; CHI, chalcone isomerase; F3H,

395

flavone 3-hydroxylase; F3'H, flavonoid 3',-hydroxylase; DFR, dihydroflavonol

396

reductase; ANS, anthocyanidin synthase; 5-GT, flavonoid-5-glucosyltransferase; GST,

397

glutathione S-transferase; DHK, dihydrokaempferol; HPLC, high-performance liquid

398

chromatography; ESI-MS/MS, elctrospray ionization tandem mass spectrometry;

399

qRT-PCR, quantitative real-time PCR; DAS, days after sowing.

400 401

Acknowledgment

402

This work was supported by National Natural Science Foundation of China (nos.

403

30871709, 30600044, 31171968) and Technology System of National Bulk Vegetable

404

Industry--Eggplant Breeding Position (CARS-25-A-06).

405

Supporting Information description

406

A table of primers used for qPCR analysis of anthocyanin biosynthetic genes and

407

associated regulatory genes in kohlrabi, a figure depicting phenotypic characterization

408

of Kolibri and Winner during all the developmental stages of vegetative growth.

409 410 411 412 413 414 415 416 417

REFERENCES: 1.

Christie, P.; Alfenito, M.; Walbot, V., Impact of low-temperature stress on general

phenylpropanoid and anthocyanin pathways: Enhancement of transcript abundance and anthocyanin pigmentation in maize seedlings. Planta 1994, 194, 541-549. 2.

Sarma, A. D.; Sharma, R., Anthocyanin-DNA copigmentation complex: mutual protection against

oxidative damage. Phytochemistry 1999, 52, 1313-1318. 3.

Bradshaw, H. D.; Schemske, D. W., Allele substitution at a flower colour locus produces a

ACS Paragon Plus Environment

Page 20 of 37

Page 21 of 37

Journal of Agricultural and Food Chemistry

418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461

pollinator shift in monkeyflowers. Nature 2003, 426, 176-8. 4.

Lorenc-Kukula, K.; Jafra, S.; Oszmianski, J.; Szopa, J., Ectopic expression of anthocyanin

5-o-glucosyltransferase in potato tuber causes increased resistance to bacteria. Journal of agricultural and food chemistry 2005, 53, 272-81. 5.

Castellarin, S. D.; Pfeiffer, A.; Sivilotti, P.; Degan, M.; Peterlunger, E.; G, D. I. G., Transcriptional

regulation of anthocyanin biosynthesis in ripening fruits of grapevine under seasonal water deficit. Plant, cell & environment 2007, 30, 1381-99. 6.

Jin, H.; Cominelli, E.; Bailey, P.; Parr, A.; Mehrtens, F.; Jones, J.; Tonelli, C.; Weisshaar, B.;

Martin, C., Transcriptional repression by AtMYB4 controls production of UV-protecting sunscreens in Arabidopsis. The EMBO journal 2000, 19, 6150-61. 7.

Hannum, S. M., Potential impact of strawberries on human health: a review of the science.

Critical reviews in food science and nutrition 2004, 44, 1-17. 8.

Guarnieri, S.; Riso, P.; Porrini, M., Orange juice vs vitamin C: effect on hydrogen

peroxide-induced DNA damage in mononuclear blood cells. The British journal of nutrition 2007, 97, 639-43. 9.

Toufektsian, M. C.; de Lorgeril, M.; Nagy, N.; Salen, P.; Donati, M. B.; Giordano, L.; Mock, H. P.;

Peterek, S.; Matros, A.; Petroni, K.; Pilu, R.; Rotilio, D.; Tonelli, C.; de Leiris, J.; Boucher, F.; Martin, C., Chronic dietary intake of plant-derived anthocyanins protects the rat heart against ischemia-reperfusion injury. J Nutr 2008, 138, 747-52. 10. de Pascual-Teresa, S.; Moreno, D. A.; Garcia-Viguera, C., Flavanols and anthocyanins in cardiovascular health: a review of current evidence. International journal of molecular sciences 2010, 11, 1679-703. 11. Paredes-Lopez, O.; Cervantes-Ceja, M. L.; Vigna-Perez, M.; Hernandez-Perez, T., Berries: improving human health and healthy aging, and promoting quality life--a review. Plant foods for human nutrition 2010, 65, 299-308. 12. Butelli, E.; Titta, L.; Giorgio, M.; Mock, H. P.; Matros, A.; Peterek, S.; Schijlen, E. G.; Hall, R. D.; Bovy, A. G.; Luo, J.; Martin, C., Enrichment of tomato fruit with health-promoting anthocyanins by expression of select transcription factors. Nature biotechnology 2008, 26, 1301-8. 13. Meiers, S.; Kemeny, M.; Weyand, U.; Gastpar, R.; von Angerer, E.; Marko, D., The anthocyanidins cyanidin and delphinidin are potent inhibitors of the epidermal growth-factor receptor. Journal of agricultural and food chemistry 2001, 49, 958-62. 14. Williams, R. J.; Spencer, J. P.; Rice-Evans, C., Flavonoids: antioxidants or signalling molecules? Free radical biology & medicine 2004, 36, 838-49. 15. Sparvoli, F.; Martin, C.; Scienza, A.; Gavazzi, G.; Tonelli, C., Cloning and molecular analysis of structural genes involved in flavonoid and stilbene biosynthesis in grape (Vitis vinifera L.). Plant molecular biology 1994, 24, 743-755. 16. Winkel-Shirley, B., Flavonoid biosynthesis. A colorful model for genetics, biochemistry, cell biology, and biotechnology. Plant physiology 2001, 126, 485-93. 17. Harborne, J. B.; Williams, C. A., Advances in flavonoid research since 1992. Phytochemistry 2000, 55, 481-504. 18. Guo, N.; Cheng, F.; Wu, J.; Liu, B.; Zheng, S.; Liang, J.; Wang, X., Anthocyanin biosynthetic genes in Brassica rapa. BMC genomics 2014, 15, 426. 19. Grotewold, E., The genetics and biochemistry of floral pigments. Annual review of plant biology 2006, 57, 761-80.

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505

20. Shirley, B. W., Flavonoid biosynthesis: ‘new’ functions for an ‘old’ pathway. Trends in plant science 1996, 1, 377-382. 21. Bogs, J.; Ebadi, A.; McDavid, D.; Robinson, S. P., Identification of the Flavonoid Hydroxylases from Grapevine and Their Regulation during Fruit Development. Plant physiology 2006, 140, 279-291. 22. Springob, K.; Nakajima, J.; Yamazaki, M.; Saito, K., Recent advances in the biosynthesis and accumulation of anthocyanins. Natural product reports 2003, 20, 288-303. 23. Boss, P. K.; Davies, C.; Robinson, S. P., Expression of anthocyanin biosynthesis pathway genes in red and white grapes. Plant molecular biology 1996, 32, 565-9. 24. Hichri, I.; Barrieu, F.; Bogs, J.; Kappel, C.; Delrot, S.; Lauvergeat, V., Recent advances in the transcriptional regulation of the flavonoid biosynthetic pathway. Journal of experimental botany 2011, 62, 2465-83. 25. Yuan, Y.; Chiu, L. W.; Li, L., Transcriptional regulation of anthocyanin biosynthesis in red cabbage. Planta 2009, 230, 1141-53. 26. Gonzalez, A.; Zhao, M.; Leavitt, J. M.; Lloyd, A. M., Regulation of the anthocyanin biosynthetic pathway by the TTG1/bHLH/Myb transcriptional complex in Arabidopsis seedlings. The Plant journal : for cell and molecular biology 2008, 53, 814-27. 27. Nesi, N.; Debeaujon, I.; Jond, C.; Pelletier, G.; Caboche, M.; Lepiniec, L., The TT8 gene encodes a basic helix-loop-helix domain protein required for expression of DFR and BAN genes in Arabidopsis siliques. Plant Cell 2000, 12, 1863-78. 28. Payne, C. T.; Zhang, F.; Lloyd, A. M., GL3 encodes a bHLH protein that regulates trichome development in arabidopsis through interaction with GL1 and TTG1. Genetics 2000, 156, 1349-62. 29. Zhang, F.; Gonzalez, A.; Zhao, M.; Payne, C. T.; Lloyd, A., A network of redundant bHLH proteins functions in all TTG1-dependent pathways of Arabidopsis. Development 2003, 130, 4859-69. 30. Espley, R. V.; Hellens, R. P.; Putterill, J.; Stevenson, D. E.; Kutty-Amma, S.; Allan, A. C., Red colouration in apple fruit is due to the activity of the MYB transcription factor, MdMYB10. The Plant journal : for cell and molecular biology 2007, 49, 414-27. 31. Chiu, L. W.; Zhou, X.; Burke, S.; Wu, X.; Prior, R. L.; Li, L., The purple cauliflower arises from activation of a MYB transcription factor. Plant physiology 2010, 154, 1470-80. 32. Feng, S.; Wang, Y.; Yang, S.; Xu, Y.; Chen, X., Anthocyanin biosynthesis in pears is regulated by a R2R3-MYB transcription factor PyMYB10. Planta 2010, 232, 245-55. 33. Butelli, E.; Licciardello, C.; Zhang, Y.; Liu, J.; Mackay, S.; Bailey, P.; Reforgiato-Recupero, G.; Martin, C., Retrotransposons control fruit-specific, cold-dependent accumulation of anthocyanins in blood oranges. Plant Cell 2012, 24, 1242-55. 34. Zhang, Y.; Hu, Z.; Chu, G.; Huang, C.; Tian, S.; Zhao, Z.; Chen, G., Anthocyanin Accumulation and Molecular Analysis of Anthocyanin Biosynthesis-Associated Genes in Eggplant (Solanum melongena L.). Journal of agricultural and food chemistry 2014. 35. Mathews, H.; Clendennen, S. K.; Caldwell, C. G.; Liu, X. L.; Connors, K.; Matheis, N.; Schuster, D. K.; Menasco, D. J.; Wagoner, W.; Lightner, J.; Wagner, D. R., Activation tagging in tomato identifies a transcriptional regulator of anthocyanin biosynthesis, modification, and transport. Plant Cell 2003, 15, 1689-703. 36. Borevitz, J. O.; Xia, Y.; Blount, J.; Dixon, R. A.; Lamb, C., Activation Tagging Identifies a Conserved MYB Regulator of Phenylpropanoid Biosynthesis. The Plant Cell 2000, 12, 2383-2393. 37. Park, K. I.; Ishikawa, N.; Morita, Y.; Choi, J. D.; Hoshino, A.; Iida, S., A bHLH regulatory gene in the common morning glory, Ipomoea purpurea, controls anthocyanin biosynthesis in flowers,

ACS Paragon Plus Environment

Page 22 of 37

Page 23 of 37

Journal of Agricultural and Food Chemistry

506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549

proanthocyanidin and phytomelanin pigmentation in seeds, and seed trichome formation. The Plant journal : for cell and molecular biology 2007, 49, 641-54. 38. Feyissa, D. N.; Lovdal, T.; Olsen, K. M.; Slimestad, R.; Lillo, C., The endogenous GL3, but not EGL3, gene is necessary for anthocyanin accumulation as induced by nitrogen depletion in Arabidopsis rosette stage leaves. Planta 2009, 230, 747-54. 39. Xie, X. B.; Li, S.; Zhang, R. F.; Zhao, J.; Chen, Y. C.; Zhao, Q.; Yao, Y. X.; You, C. X.; Zhang, X. S.; Hao, Y. J., The bHLH transcription factor MdbHLH3 promotes anthocyanin accumulation and fruit colouration in response to low temperature in apples. Plant, cell & environment 2012, 35, 1884-97. 40. Goldsbrough, A. P.; Tong, Y.; Yoder, J. I., Lc as a non-destructive visual reporter and transposition excision marker gone for tomato. The Plant Journal 1996, 9, 927-933. 41. Zhang, Y.; Chen, G.; Dong, T.; Pan, Y.; Zhao, Z.; Tian, S.; Hu, Z., Anthocyanin Accumulation and Transcriptional Regulation of Anthocyanin Biosynthesis in Purple Bok Choy (Brassica rapa var. chinensis). Journal of agricultural and food chemistry 2014, 62, 12366-12376. 42. Mooney, M.; Desnos, T.; Harrison, K.; Jones, J.; Carpenter, R.; Coen, E., Altered regulation of tomato and tobacco pigmentation genes caused by the delila gene of Antirrhinum. The Plant Journal 1995, 7, 333-339. 43. Jahangir, M.; Kim, H. K.; Choi, Y. H.; Verpoorte, R., Health-Affecting Compounds in Brassicaceae. Comprehensive Reviews in Food Science and Food Safety 2009, 8, 31-43. 44. Park, W. T.; Kim, J. K.; Park, S.; Lee, S. W.; Li, X.; Kim, Y. B.; Uddin, M. R.; Park, N. I.; Kim, S. J.; Park, S. U., Metabolic profiling of glucosinolates, anthocyanins, carotenoids, and other secondary metabolites in kohlrabi (Brassica oleracea var. gongylodes). Journal of agricultural and food chemistry 2012, 60, 8111-6. 45. Cartea, M. E.; Francisco, M.; Soengas, P.; Velasco, P., Phenolic compounds in Brassica vegetables. Molecules 2011, 16, 251-80. 46. Park, N. I.; Xu, H.; Li, X.; Jang, I. H.; Park, S.; Ahn, G. H.; Lim, Y. P.; Kim, S. J.; Park, S. U., Anthocyanin accumulation and expression of anthocyanin biosynthetic genes in radish (Raphanus sativus). Journal of agricultural and food chemistry 2011, 59, 6034-9. 47. Boss, P. K.; Davies, C.; Robinson, S. P., Analysis of the Expression of Anthocyanin Pathway Genes in Developing Vitis vinifera L. cv Shiraz Grape Berries and the Implications for Pathway Regulation. Plant physiology 1996, 111, 1059-1066. 48. Dubos, C.; Stracke, R.; Grotewold, E.; Weisshaar, B.; Martin, C.; Lepiniec, L., MYB transcription factors in Arabidopsis. Trends in plant science 2010, 15, 573-81. 49. Spelt, C.; Quattrocchio, F.; Mol, J. N.; Koes, R., anthocyanin1 of petunia encodes a basic helix-loop-helix protein that directly activates transcription of structural anthocyanin genes. Plant Cell 2000, 12, 1619-32. 50. Li, X.; Thwe, A. A.; Park, N. I.; Suzuki, T.; Kim, S. J.; Park, S. U., Accumulation of phenylpropanoids and correlated gene expression during the development of tartary buckwheat sprouts. Journal of agricultural and food chemistry 2012, 60, 5629-35. 51. Grotewold, E.; Sainz, M. B.; Tagliani, L.; Hernandez, J. M.; Bowen, B.; Chandler, V. L., Identification of the residues in the Myb domain of maize C1 that specify the interaction with the bHLH cofactor R. Proc Natl Acad Sci U S A 2000, 97, 13579-84. 52. Mano, H.; Ogasawara, F.; Sato, K.; Higo, H.; Minobe, Y., Isolation of a regulatory gene of anthocyanin biosynthesis in tuberous roots of purple-fleshed sweet potato. Plant physiology 2007, 143, 1252-68.

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

550 551 552 553 554 555 556 557 558

53. Espley, R. V.; Brendolise, C.; Chagne, D.; Kutty-Amma, S.; Green, S.; Volz, R.; Putterill, J.;

559

FIGURE CAPTIONS

560

Figure 1. Schematic representation of the biosynthetic pathway of the anthocyanins.

561

The names of the compounds in boxes are indicated. The enzyme names are PAL,

562

phenylalanine ammonia lyase; C4H, cinnamate 4-hydroxylase; 4CL, 4-coumarateCoA

563

ligase; CHS, chalcone synthase; CHI, chalcone isomerase; F3H, flavanone

564

3-hydroxylase; F3'H, flavanone 3'-hydroxylase; DFR, dihydroflavonol 4-reductase;

565

ANS, anthocyanidin synthase; 5-GT, flavonoid-5-glucosyltransferase; PAT, putative

566

anthocyanin transporter.

567

Figure 2. Anthocyanin analysis of different kohlrabi cultivars. (A) Photographs of the

568

different tissues of two kohlrabi cultivars (Kolibri on the left and Winner on the right)

569

used in this study. (B) Total anthocyanin content analysis of leaves, stem flesh and

570

skins in the two kohlrabi cultivars. PS (Purple skin of swollen stem); GS (Green skin

571

of swollen stem); PS (Flesh of swollen stem in purple cultivar); GS (Flesh of swollen

572

stem in green cultivar); PL (Purple leave); GL (Green leave). Error bars represent the

573

standard error of the mean (n = 3). (C) HPLC profiles of anthocyanins extracted from

574

the skins of the purple swollen stem. Peak numbers refer to the anthocyanins are listed

575

in Table 1. Structures and major cleavage of cyanidin 3-(caffeoyl) p-coumaroyl

576

(sinapoyl) diglucoside-5-glucoside in reference to peak 6 is framed in box.

Schouten, H. J.; Gardiner, S. E.; Hellens, R. P.; Allan, A. C., Multiple repeats of a promoter segment causes transcription factor autoregulation in red apples. Plant Cell 2009, 21, 168-83. 54. Walker, A. R.; Lee, E.; Bogs, J.; McDavid, D. A.; Thomas, M. R.; Robinson, S. P., White grapes arose through the mutation of two similar and adjacent regulatory genes. The Plant journal : for cell and molecular biology 2007, 49, 772-85. 55. Albert, N. W.; Lewis, D. H.; Zhang, H.; Irving, L. J.; Jameson, P. E.; Davies, K. M., Light-induced vegetative anthocyanin pigmentation in Petunia. Journal of experimental botany 2009, 60, 2191-202.

ACS Paragon Plus Environment

Page 24 of 37

Page 25 of 37

Journal of Agricultural and Food Chemistry

577

Figure 3. Expression analysis of anthocyanin biosynthetic genes in different tissues of

578

the two kohlrabi cultivars. PS (Purple skin of swollen stem); GS (Green skin of

579

swollen stem); PS (Flesh of swollen stem in purple cultivar); GS (Flesh of swollen

580

stem in green cultivar); PL (Purple leave); GL (Green leave). Error bars represent the

581

standard error of the mean (n = 3). Error bars represent the standard error of the mean

582

(n = 3). Statistical significance of the differences between samples was calculated

583

with ANOVA by paired-group comparisons. Different letters in uppercase indicate

584

significance at P < 0.01. Different letters in lowercase indicate significance at P