In flowering plants, photoperiodic flowering is controlled by a complicated network. Light is one of the most important environmental stimuli that control the timing of the transition from vegetative growth to reproductive development. Several photoreceptors, including PHYA, PHYB, CRY2, and FKF1 in Arabidopsis and their homologs (OsPHYA, OsPHYB, OsPHYC, and OsCRY2) in rice, have been identified to be related to flowering. Our previous study suggests that OsHAL3, a flavin mononucleotide-binding protein, may function as a blue-light sensor. Here, we report the identification of OsHAL3 as a positive regulator of flowering in rice. OsHAL3 overexpression lines exhibited an early flowering phenotype, whereas downregulation of OsHAL3 expression by RNA interference delayed flowering under an inductive photoperiod (short-day conditions). The change in flowering time was not accompanied by altered Hd1 expression but rather by reduced accumulation of Hd3a and MADS14 transcripts. OsHAL3 and Hd1 colocalized in the nucleus and physically interacted in vivo under the dark, whereas their interaction was inhibited by white or blue light. Moreover, OsHAL3 directly bound to the promoter of Hd3a, especially before dawn. We conclude that OsHAL3, a novel light-responsive protein, plays an essential role in photoperiodic control of flowering time in rice, which is probably mediated by forming a complex with Hd1. Our findings open up new perspectives on the photoperiodic flowering pathway.
在開(kāi)花植物中，光周期開(kāi)花受到復(fù)雜網(wǎng)絡(luò)的調(diào)控。光是最重要的環(huán)境刺激因子之一，控制著營(yíng)養(yǎng)生長(zhǎng)向生殖生長(zhǎng)轉(zhuǎn)化的時(shí)間。一些光受體，包括擬南芥的PHYA、PHYB、CRY2和FKF1，以及它們?cè)谒局械耐吹鞍譕sPHYA、OsPHYB、OsPHYC和OsCRY2等，已經(jīng)被鑒定可能與開(kāi)花相關(guān)。我們之前的研究表明黃素單核苷酸結(jié)合蛋白OsHAL3作為藍(lán)光感受蛋白發(fā)揮功能。本文我們報(bào)道了OsHAL3是水稻的開(kāi)花正調(diào)控因子。在誘導(dǎo)性光周期條件（短日照條件）下，OsHAL3過(guò)表達(dá)株系表現(xiàn)出早花表型，而通過(guò)RNA干涉下調(diào)OsHAL3表達(dá)會(huì)延遲開(kāi)花。開(kāi)花時(shí)間的變化沒(méi)有伴隨著Hd1表達(dá)的改變，相反地，Hd3a和MADS14轉(zhuǎn)錄的積累降低。OsHAL3和Hd1共定位在細(xì)胞核，黑暗條件下在體內(nèi)能物理互作，而它們的相互作用被白光和藍(lán)光抑制。此外，OsHAL3直接與Hd3a啟動(dòng)子結(jié)合，特別是在黎明前。我們認(rèn)為，OsHAL3是新的光敏感蛋白，在光周期調(diào)控水稻的開(kāi)花時(shí)間中發(fā)揮重要作用，這可能是通過(guò)與Hd1形成復(fù)合物來(lái)介導(dǎo)的。我們的發(fā)現(xiàn)為光周期開(kāi)花通路提供了新的理解。