Understanding pathogen resistance in fruit
the initial appearance of the mold and ultimately produced significantly smaller fruit lesions at day 8. Higher levels of soluble solids were present in the treated fruit, suggesting these peaches were generally healthier than the control group. In addition, the researchers analyzed protein samples from the peaches by 2DE and noted that after 24 hours, 43 proteins were regulated differently in yeast-treated fruit and 31 proteins showed altered expression in SA-treated fruit. Of these proteins, seven were regulated by both treatments. With
Other members of this group of proteins may be involved in the repair of Every year, millions of tons of fruits, oxidative-damage intermediates. vegetables, and grains are lost to the The researchers also identified sevglobal market because of spoilage eral pathogenesis-related (PR) proteins, caused by pathogens such as peach including major cherry allergen Pru mold and wheat smut. “Produce av 1.0202 and cherry allergen PRUA1, degeneration may result directly in which had been noted in studies with enormous losses both of quality and other fruits. Previous studies have sugmarket values, which indirectly affect gested that PR proteins are associated development of agriculture and the with SAR and not ISR, but given that food industry,” says Shiping Tian of the each preventative treatment induced Chinese Academy of Sciences (CAS). at least one PR protein, the researchFurthermore, she says that consumers ers suggest that this theory may need are growing increasingly worried about rethinking. the links between food qualFrom Tian’s perspective, ity and human health. however, the most interesting (a) (b) (c) Concerns about the effects result was that the treatment of pesticides have led farmers response also included enand researchers to explore zymes involved in glycolysis other preventative measures, and the tricarboxylic acid including those that stimucycle. “Sugar is an important late the plants’ natural decomponent in fruit, and some fenses, but the mechanisms sugars, such as mannose and of these processes are poorly trehalose, are a group of meunderstood. In this issue of tabolites termed ‘compatible JPR (pp 1677–1688), however, solutes’, which play a role in Tian and colleagues at CAS plant–pathogen interaction,” and its graduate school used she says. “Elicitor treatments proteomics to understand the may change the metabolic pathways involved in induced pathway in the fruit.” resistance in peach fruit Identifying the proteins inagainst blue mold rot (Penivolved in infection resistance cillium expansum), a major is only the first step in undersource of postharvest decay. standing the underlying mechThe researchers focused anism of defense. Looking their efforts on two forms of forward, Tian says, “We expect Not very appetizing. Development of blue mold in peaches after induced resistance: systemic to investigate the response treatment with (a) sterile distilled water (control), (b) yeast, and acquired resistance (SAR), mechanism of fruit at different (c) SA. which is an intrinsic wholedevelopmental stages to biotic plant response to pathogen and abiotic stress in disease MS/MS, they then identified the 25 pro attack, and induced systemic resistance defense. In addition, further studies on (ISR), in which the response is stimuteins exhibiting the most significant the protein and sugar metabolisms will lated by an external growth-promoting regulatory effects. be necessary to illuminate the mechaorganism. Previous studies showed Of particular interest were six antinisms of ISR and SAR.” that salicylic acid (SA) is a key signaling oxidant proteins, including catalase Tian recognizes that it may be some molecule involved in triggering plant and glutathione peroxidase, that were time before the results translate into defense responses through SAR and significantly up-regulated by one or practical applications aimed at improvthat the antagonist yeast Pichia memboth treatments. As Tian explains, this ing food production and transport, but branefaciens is capable of triggering ISR runs counter to one model of SA action. she remains confident that the use of in some plant species. In that model, SA inhibits hydrogen such technologies will be an effective To better understand the molecular peroxide degradation by catalase, approach to reducing the application events behind SAR and ISR, Tian and leaving hydrogen peroxide to act as a of chemical fungicides. On the basis colleagues pretreated peaches with secondary messenger for other defense of this and other studies, she strongly water, an SA solution, or a P. membranepathways. Instead, catalase levels and believes that the combined approach of faciens suspension before making small activity are significantly increased. applying yeasts and nontoxic chemicals wounds in the fruit. They then divided “The antioxidant proteins may mediate such as SA is a better way to control the fruit into two groups: one was left the concentration of reactive oxygen postharvest decay than the use of each alone, and the other was inoculated species, which act as the signal during agent individually. with P. expansum. Pretreatment slowed pathogen–plant interaction,” she says. —Randall C Willis
Journal of Proteome Research • Vol. 6, No. 5, 2007 1639
