( s on the hypocotyl (stem just above the...)Scientists find microRNAs regulate plant development

s on the hypocotyl (stem just above the root) when treated with auxin but the ago1 mutants do not. Dr. Bellini and her colleagues found that the mutant plants over-accumulate ARF17 mRNA within the hypocotyl, pointing to ARF17 as a major regulator of adventitious rooting and microRNA-mediated regulation as a major regulator of ARF17.

In a third report, Dr. Nam-Hai Chua of Rockefeller University in New York and scientists at the Temasek Life Science Laboratories, Singapore, and the Chinese Academy of Sciences in Beijing show that microRNA is important in the regulation of a transcription factor that is induced by auxin, called NAC1. NAC1 functions in other aspects of the auxin response, such as the formation of lateral roots (roots that grow off the main tap root below ground, as opposed to the adventitious roots that grow off of the stem or other above-ground plant parts). Like ARF17, NAC1 mRNA contains a stretch of sequence that is complementary to microRNAs, and thus shows potential for microRNA-mediated regulation. In experiments analogous to those of Bartel's group, Chua and colleagues created transgenic Arabidopsis plants that produce a version of NAC1 that is resistant to microRNA-mediated cleavage. Compared to wild-type plants, the transgenic plants overaccumulated NAC1 mRNA and produced more lateral roots. It was also found that accumulation of the microRNA that targets NAC1 mRNA is induced by auxin. The pattern of induction suggested a model wherein auxin induction of NAC1 mRNA is later followed by induction of the microRNA responsible for NAC1 mRNA cleavage. MicroRNA-mediated regulation of gene expression therefore appears to be an important mechanism for fine-tuning auxin signaling during plant development.

These reports provide significant new information on microRNA-mediated regulation of plant development and show that microRNAs play important roles in regulating the auxin response pathway.

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Source:American Society of Plant Biologists

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