Seeds of a Micro Revolution

Courtesy of Allison C. Mallory, Whitehead Institute for Biomedical Research

A scanning electron micrograph of Arabidopsis shows the importance of microRNAs in development. A mutation in the CUC1 transcription factor rendering it impermeable to silencing by miR-164 results in flowers that have extra petals, missing sepals and altered floral organ position (at right).

Among structural and regulatory RNAs, the newest kids on the block have sparked a flurry of breakthrough discoveries in just three years. Tiny RNAs, called microRNAs (miRNAs), roughly 22 nucleotides long, are processed from stem-loop transcripts and bind and direct the repression of target mRNAs. Though both short interfering RNAs (siRNAs) and miRNAs are processed from double-stranded precursor transcripts by the Dicer nuclease, other events appear to diverge.

This issue's Hot Papers focus on the discovery of miRNAs in plants. David Bartel's group at the Whitehead Institute for Biomedical Research and the Massachusetts Institute of Technology,12 and ...