( The plant hormone indole-3-acetic acid ...)Scientists find microRNAs regulate plant development

The plant hormone indole-3-acetic acid (IAA), commonly referred to as auxin, plays a major role in regulating plant growth and development. Auxin influences development by affecting the expression of numerous genes that control the processes of cell division and cell expansion in specific plant tissues at specific stages during the plant life cycle - e.g. for leaves, roots, and floral organs to develop in the correct patterns and correct time sequence. Research reported in The Plant Cell shows that microRNAs control the accumulation of transcription factor proteins that regulate the expression of genes in the auxin response pathway.

Messenger RNA (mRNA) molecules are encoded by genes and are themselves templates for the proteins that carry the main metabolic functions in a cell. The mRNA levels in a cell are fine tuned by different mechanisms, one of which is driven by microRNA molecules. MicroRNAs are ~22 nucleotide long RNA molecules that provide substrate specificity to a protein complex known as the RNA-induced silencing complex. Within the complex, microRNAs are thought to bind to mRNA molecules containing a complementary stretch of RNA sequence. The complex then cleaves the mRNA into smaller pieces, thereby preventing translation of the protein it encodes, and thus inhibiting or "silencing" gene expression. mRNAs corresponding to several regulatory genes that mediate auxin responses contain short stretches of sequence that are complementary to microRNAs, and therefore have been considered potential targets of microRNA-mediated regulation. One of these targets is the transcription factor AUXIN RESPONSE FACTOR17 (ARF17), which is thought to repress the expression of a number of other genes involved in auxin responses.

Dr. Bonnie Bartel at Rice University in Houston, TX together with Drs. David Bartel and Allison Mallory at the Massachusetts Institute of Technology and the Whitehead Institute for Biomedical Research in Cambridge, MA report experime
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Source:American Society of Plant Biologists

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