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Abstract

A drastic developmental transition is the switch from vegetative to reproductive development. The initiation of flowering requires an endogenous developmental program to specify the floral identity of the new structures that arise at the shoot apex. Genetic analysis has identified four main signals and corresponding pathways that control flowering time in Arabidopsis: the photoperiod, autonomous, vernalization, and gibberellin pathways. Overexpressing of one Arabidopsis microRNA (miRNA), miR156, leads to a plant with delayed flowering and shortened plastochrons (the interval between formation of primordia at the shoot apex) (Schwab et al., 2005). miR156 targets a group of genes encoding plant-specific transcription factors, named squamosa promoter binding protein-like (SPL) proteins. Overexpression of a miR156-resistant form of SPL3 (rSPL3) accelerates flowering in both long day and short day condition. Using mis-expression, promoter GUS (β-glucuronidase) reporter fusions, and genetic analyses, we show here that miR156 regulates SPL3 levels in leaves and that SPL3 promotes flowering in a FT (FLOWERING LOCUS T)-dependent manner. We will discuss the position of SPL/miR156 in the current framework of flower signal integration.