Rice tillering, a key architecture trait determining grain yield, is highly regulated by a class of newly identified phytohormones, strigolactones (SLs). However, the whole SL signaling pathway from the receptor to downstream transcription factors to finally inhibit tillering remains unrevealed. In this study, we first found that brassinosteroids (BRs) strongly enhance tillering by promoting bud outgrowth in rice, which is largely different from the function of BRs in Arabidopsis. Genetic and biochemical analyses indicated that both the SL and BR signaling pathways control rice tillering by regulating the stability of D53 and/or the OsBZR1–RLA1–DLT module, a transcriptional complex in the rice BR signaling pathway. We further found that D53 interacts with OsBZR1 to inhibit the expression of FC1, a local inhibitor of tillering, and that this inhibition depends on direct DNA binding by OsBZR1, which recruits D53 to the FC1 promoter in rice buds. Taken together, these findings uncover a mechanism illustrating how SLs and BRs coordinately regulate rice tillering via the early responsive gene FC1.
水稻分蘗是決定水稻產(chǎn)量的一個(gè)重要形態(tài)性狀，嚴(yán)格受一類新發(fā)現(xiàn)的植物激素-獨(dú)角金內(nèi)酯（SLs）調(diào)控。然而，從受體到下游轉(zhuǎn)錄因子到最終抑制分蘗的整個(gè)SL信號(hào)通路仍未被揭示。在本研究中，我們首次發(fā)現(xiàn)油菜素甾醇（BRs）通過促進(jìn)芽的生長(zhǎng)而促進(jìn)水稻分蘗，這與BRs在擬南芥中的作用有很大的不同。遺傳和生化分析表明，SL和BR信號(hào)通路通過調(diào)節(jié)D53和/或OsBZR1–RLA1–DLT模塊（水稻BR信號(hào)通路中的轉(zhuǎn)錄復(fù)合物）的穩(wěn)定性來控制水稻分蘗。我們進(jìn)一步發(fā)現(xiàn)，D53與OsBZR1相互作用，抑制分蘗局部抑制因子FC1的表達(dá)，這種抑制作用依賴于OsBZR1直接與DNA結(jié)合，后者募集D53與水稻芽中的FC1啟動(dòng)子結(jié)合。綜上所述，這些發(fā)現(xiàn)揭示了SLs和BRs通過早期反應(yīng)基因FC1協(xié)調(diào)調(diào)控水稻分蘗的機(jī)制。