FLORAL DEVELOPMENT Hormone Regulates MicroRNAs in Plants

The phytohormone gibberellin (GA) controls floral initiation and development. An important GA-controlled signaling pathway involves GAMYB, a transcriptional regulator that binds to a GA-response element (GARE) in the regulatory regions of GA-activated genes. Target genes include those that encode enzymes that release nutrients from the endosperm during seed germination. In Arabidopsis, GAMYB proteins activate the expression of LEAFY, a floral meristem identity gene. Achard et al. report that in Arabidopsis, a single-stranded microRNA (21 nucleotides) called miR159, with sequence complementarity to GAMYB-encoding transcripts, targets the transcriptional regulators for cleavage. Overexpression of miR159 in transgenic plants reduced expression of GAMBY transcript and protein. Transgenic plants also had reduced LEAFY expression and delayed flowering time. This suggests that miR159 modulates GA-mediated development through GAMYB activity. Paradoxically, miR159 appears to be positively regulated by GA, revealing a complex relationship between GA, miR159, and GAMYB expression that requires further clarification. MiR159 expression also appears to be negatively regulated by DELLA proteins, transcriptional repressors of the GA response. Thus, as observed in Drosophila, plant microRNAs appear to be controlled by hormones as well.

P. Achard, A. Herr, D. C. Baulcombe, N. P. Harberd, Modulation of floral development by gibberellin-regulated microRNA. Development 131, 3357-3365 (2004). [Abstract] [Full Text]