( nts using transgenic Arabidopsis plants...)Scientists find microRNAs regulate plant development

nts using transgenic Arabidopsis plants that produce a version of ARF17 mRNA that resists microRNA-mediated cleavage. The plants showed increased accumulation of ARF17 mRNA and altered levels of mRNAs corresponding to several genes that may be regulated by ARF17. These changes were correlated with dramatic development defects in leaves, roots, and flowers, showing that microRNA-mediated regulation of ARF17 is essential for normal plant development.

Bonnie Bartel notes that "we have known for several years now that microRNAs regulate genes implicated in auxin responses; with these three reports, we are beginning to understand the consequences of this regulation for the development of the plant." David Bartel adds, "We were particularly struck by the unusual quadrilaterally symmetric seedlings we uncovered in our study. This result implies that the Arabidopsis embryo relies on microRNA restriction of ARF17 activity to achieve normal bilateral symmetry."

A second report focuses on the function of the protein ARGONAUTE1 (AGO1), a major component of the RNA-induced silencing complex in Arabidopsis. There are many AGO1-like proteins in animals and other eukaryotes as well, indicating that the RNA-induced silencing complex is of ancient evolutionary origin, and that microRNA-mediated regulation of gene expression is shared among many eukaryotes. Arabidopsis ago1 mutants lacking the AGO1 protein have numerous severe developmental defects, supporting the notion that regulation by microRNAs is critical for normal plant growth. Dr. Catherine Bellini at The Swedish University of Agricultural Sciences in Umeå, Sweden and colleagues at several other institutions noticed that the ago1 mutant failed to form adventitious roots - a type of root that develops from aerial parts of the plant and is important for propagation through cuttings. Auxin is known to be a major regulator of adventitious root formation and normal Arabidopsis plants form multiple adventitious root
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Source:American Society of Plant Biologists

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