It’s a Small RNA World, After All

Small RNAs (sRNAs) can regulate transcript and protein abundance. Previously, they have been identified using traditional cloning approaches, which has limited how many could be characterized. Now, the Meyers and Green laboratories have used massively parallel signature sequencing technology to find over 1.5 million sRNAs in Arabidopsis thaliana. These new sRNAs reveal a greater-than-expected potential role for sRNAs in gene regulation, preferential expression or usage of sRNAs in flowers, and the prospect of targeted sRNA-mediated regulation of pseudogenes. In addition, new plant microRNAs have been identified, some of which may be unique to Arabidopsis. Small RNAs (sRNAs) are 20- to 26-nucleotide noncoding RNAs that regulate transcript and protein abundance via multiple mechanisms (1, 2). MicroRNAs (miRNAs) are generated by endonucleolytic cleavage of hairpin precur-sor transcripts by Dicer ribonuclease (RNase