MicroRNAs (miRNAs) and small interfering RNAs (siRNAs) have been isolated from all complex eukaryotes examined to date. Plant mRNA cleavage is mechanistically analogous to that involving siRNAs, is initiated by miRNAs, and can mediate posttranscriptional regulation. The mechanisms regulating CIN expression—a member of the TCP family of DNA-binding proteins—have been unclear, but even in wildtype (WT) plants, distinct RNA patterns are observed as a result of differential transcription or alterations in transcript stability. In the August 20 Nature, Javier Palatnik and colleagues at The Max Planck Institute for Developmental Biology identify a miRNA-producing locus that regulates cleavage of several TCP genes involved in leaf development. Their findings demonstrate for the first time the direct involvement of miRNA cleavage in a plant biological process (Nature, DOI:10.1038/nature01958, August 20, 2003).

Palatnik at al. examined the global expression profile for an Arabodopsis thaliana mutant jaw-D (phenotypically similar to the...

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