Modulation of floral development by a gibberellin-regulated microRNA

Abstract

Floral initiation and floral organ development are both regulated by the phytohormone gibberellin (GA). For example, in short-day photoperiods, the Arabidopsis floral transition is strongly promoted by GA-mediated activation of the floral meristem-identity gene LEAFY. In addition,anther development and pollen microsporogenesis depend on GA-mediated opposition of the function of specific members of the DELLA family of GA-response repressors. We describe the role of a microRNA (miR159) in the regulation of short-day photoperiod flowering time and of anther development. MiR159 directs the cleavage of mRNA encoding GAMYB-related proteins. These proteins are transcription factors that are thought to be involved in the GA-promoted activation of LEAFY, and in the regulation of anther development. We show that miR159 levels are regulated by GA via opposition of DELLA function, and that both the sequence of miR159 and the regulation of miR159 levels by DELLA are evolutionarily conserved. Finally, we describe the phenotypic consequences of transgenic over-expression of miR159. Increased levels of miR159 cause a reduction in LEAFY transcript levels, delay flowering in short-day photoperiods, and perturb anther development. We propose that miR159 is a phytohormonally regulated homeostatic modulator of GAMYB activity, and hence of GAMYB-dependent developmental processes.

MicroRNAs and their regulatory roles in animals and plants

“…Overexpression of miR172 inhibited translation of AP2 and AP2-like mRNAs, and resulted in early flowering and disrupting the specification of floral organ identity in Arabidopsis and maize (Aukerman and Sakai, 2003;Chen, 2004;Lauter et al, 2005). miR159, miR156, and miR171 are also involved in phase change and floral development (Llave et al, 2002;Achard et al, 2004;Schwab et al, 2005). miR171 is predominantly expressed in inflorescence and floral tissues instead of in leaf and other vegetative tissues (Llave et al, 2002).…”

“…miR171 is predominantly expressed in inflorescence and floral tissues instead of in leaf and other vegetative tissues (Llave et al, 2002). Overexpression of miR159 results in a low level expression of LEAFY and further perturbed anther development and delayed flowering in a shortday photoperiod (Achard et al, 2004). miR156-affected plant phase transition, including quickly initiating the formation of rosette leaves, by negatively regulating the expression of a Squamosa promoter binding protien like (SPL) plant-specific transcription factor (Schwab et al, 2005).…”

Floral patterning defects induced by Arabidopsis APETALA2 and microRNA172 expression in Nicotiana benthamiana

“…Recent studies have uncovered the role of microRNAs (miRNAs), ~21-nucleotide noncoding RNAs, as regulators of floral patterning gene expression in Arabidopsis flower development (Aukerman and Sakai 2003;Schmid et al 2003;Achard et al 2004;Chen 2004;Mallory et al 2004a;Baker et al 2005;Millar and Gubler 2005). Plant miRNAs regulate cognate protein coding RNAs through either transcript cleavage or translational inhibition or both (reviewed in Bartel and Bartel 2003;Carrington and Ambros 2003;Bartel 2004;Dugas and Bartel 2004;He and Hannon 2004;Mallory and Vaucheret 2004;Kidner and Martienssen 2005;Chen 2005;Valencia-Sanchez et al 2006).…”

Recent developments in understanding the mechanism and functions of microRNAs

“…GAMYB mediates gibberellic aciddependent pathway in plants and regulates GA-activated genes. GA regulates miR-159 activity and miR-159 directs the cleavage of mRNA encoding GAMYB-related proteins like MYB33 and MYB65 [44]. Overexpression of miR-159 causes the late flowering phenotype, whereas plants expressing the miRNAresistant version of MYB33 leads to developmental defects like hyponastic leaves [45,46].…”