CHEMICAL & ENGINEERING
NBWfllfllfflnHBBIffiB» MAY 30. 2005 -I EDITED BY WILLIAM 0. SCHULZ i JANËT S. IDÔDD
PLANT
BIOCHEMISTRY
AUXIN'S ACTION EXPLAINED Target of ubiquitous plant hormone and related herbicides identified
changes to the plasma membrane. The discovery of a target for auxin may also affect the hunt for better herbicides, Estelle notes. Synthetic auxinlike molecules— particularly 2,4-dichlorophenoxyacetic acid (commonly known as 2,4-D)—find widespread use as herbicides. These herbicides b i n d T I R l , too, Estelle notes. "Now that we know what the receptor is, we can work on how auxin is interacting with the receptor. It might be possible to design new auxinlike herbicides that are more effective or specialized for particular weeds." The impact ofthe discovery of this novel receptor also maybe felt beyond the plant world, Estelle suggests. 'This is the first instance where a small molecule directly regulates the protein degradation machinery" he notes. "It's possible that there are other instances
Auxin
2Λ-Ρ
teinTIRl, part of the multiprotein complex that tags proteins plant hormone auxin was BROW OR DIE for destruction in plants. The discovered, scientists have Auxin regulatess finally identified one of the pro- binding of auxin toTIRl attracts plant growth and a family of proteins (the Aux/ teins targeted by this small moldevelopment. ecule (Nature 2005,435,441 and IAAs) that otherwise prevent the Synthetic variaactivation of certain genes re 446). The long-awaited discovtions like 2,4-D ery ofauxin's target will help plant quired for plant development. Up are widely used on binding TIR1, however, these biologists determine how plant as herbisides. proteins are tagged for degrada cells detect and respond to this tion. Their destruction gives the hormone. green light to plant development. Auxin (indole-3-acetic acid) It's likely that more auxin re plays a critical role in plant develceptors await discovery notes Alan opment, controlling everything from cell growth to cell division to cell specialization. Auxin causes plants to grow their roots down into the soil and their shoots up toward the sun. Strawberry plants depend on the auxin produced by their seeds to grow juicy red fruit. "To date, no plant unable to synthesize auxin has been found," notes plant biologist Judy Callis of the University of California, Davis, in a commentary accompanying the Nature papers. Ifet no one has been able to figure out exacdy how cells sense the presence of auxin, because despite many years of effort, no one had found an auxin receptor capable of mediating auxin-induced changes in transcription, Callis tells C&EN. Two independent teams of plant biologists have now discovered such an auxin receptor. SteM.Jones, a cell biologist at the Uni- I where degradation of other pro- I AUXIN EXPLORER fan Kepinski and Ottoline Leyser teins—potentially those that have Estelle and his team of the University of %rk, in En- versity ofNorth Carolina, Chapel Hill. He suggests that plant cells an important role in cancer or othused the model plant gland, and Nihal Dharmasiri, Sunethra Dharmasiri, and Mark may rely on the previously idener aspects of animal developArabidopsis thaliana to Estelle of Indiana University each tified auxin-binding protein ment—are regulated by small moltrack down auxin's report that auxin binds to the proABP1 to drive auxin-regulated I ecules."—AMANDA YARNELL I protein target.
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OME 7 0 YEARS AFTER T H E
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