The making of a bushy grass with a branched flowering stem: Key rice plant architecture traits regulated by RFL the rice LFY homolog.

In Arabidopsis thaliana, a eudicot species, the transcription factor LFY is expressed throughout the floral meristem and promotes their formation. The expression pattern of the rice LFY homolog-RFL shows distinct differences from that of its Arabidopsis counterpart. In the March issue of PNAS (2008) we have shown the temporally-regulated high-level expression of RFL in the apical meristem is necessary for its transition to an inflorescence meristem and thus to initiate flowering. RFL controls the time taken for flowering, by activating integrators of flowering signals such as OsSOC1 and RFT1. Further, the dynamic pattern of RFL expression in the branching inflorescence meristem (panicle) and in vegetative axillary meristems (tiller buds) is required for panicle branching and tiller outgrowth. Thus RFL functions determine the architecture of the rice plant. Here we propose a plausible model for a regulatory feedback loop between RFL and OsSOC1/RFT1 in controlling the vegetative to flowering phase transition. We discuss the possibility that non-cell autonomous RFL functions may also regulate signaling the net outcome of which determines the rice plant body plan.