SERRATE: a new player on the plant microRNA scene.

MicroRNAs (miRNAs) function as sequence-specific guides that control gene expression by post-transcriptional gene silencing. Many miRNAs influence plant development by regulating the accumulation of transcripts that encode transcription factors. Mutants defective in miRNA accumulation, such as dcl1, hen1, hyl1 and ago1, have pleiotropic developmental phenotypes. The serrate-1 (se-1) mutant of Arabidopsis also shows a highly pleiotropic phenotype, which overlaps with the phenotypes of mutants defective in miRNA accumulation. Although it has been proposed that SERRATE (SE) functions specifically in miRNA-mediated repression of the leaf polarity genes PHABULOSA and PHAVOLUTA, microarray analysis shows upregulation of many genes known to be the targets of miRNAs in se-1. We show that SE is a general regulator of miRNA levels affecting the processing of primary miRNA to miRNA.