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DEVELOPMENT AND HORMONE ACTION

Analysis of PHOTOPERIOD SENSITIVITY5 Sheds Light on the Role of Phytochromes in Photoperiodic Flowering in Rice^1,[W]

Instituto Valenciano de Investigaciones Agrarias, Carretera Moncada-Naquera Km 7.5, 46113 Moncada, Spain (F.A., M.T., C.D.); and Department of Plant Sciences and Bio5 Institute, University of Arizona, Tucson, Arizona 85721 (D.W.G.)

A great number of plants synchronize flowering with day length. In rice (Oryza sativa), photoperiod is the primary environmental cue that triggers flowering. Here, we show that the s73 mutant, identified in a -irradiated Bahia collection, displays early flowering and photoperiodic insensitivity due to a null mutation in the PHOTOPERIOD SENSITIVITY5 (SE5) gene, which encodes an enzyme implicated in phytochrome chromophore biosynthesis. s73 mutant plants show a number of alterations in the characteristic diurnal expression patterns of master genes involved in photoperiodic control of flowering, resulting in up-regulation of the floral integrator Heading date3a (Hd3a). Early heading date1 (Ehd1), an additional rice floral activator, was also highly expressed in the s73 mutant, suggesting that SE5 represses Ehd1 in wild-type plants. Silencing of Ehd1 in both Bahia and s73 backgrounds indicated that SE5 regulates Ehd1 expression. The data also indicate that SE5 confers photoperiodic sensitivity through regulation of Hd1. These results provide direct evidence that phytochromes inhibit flowering by affecting both Hd1 and Ehd1 flowering pathways.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Concha Domingo (domingo_concar{at}gva.es).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.139097

^* Corresponding author; e-mail domingo_concar{at}gva.es.

Received March 30, 2009; accepted August 10, 2009; published August 12, 2009.