Strigolactones (SLs), a group of carotenoid derived terpenoid lactones, are root-to-shoot phytohormones suppressing shoot branching by inhibiting the outgrowth of axillary buds. DWARF 53 (D53), the key repressor of the SL signaling pathway, is speculated to regulate the downstream transcriptional network of the SL response. However, no downstream transcription factor targeted by D53 has yet been reported. Here we report that Ideal Plant Architecture 1 (IPA1), a key regulator of the plant architecture in rice, functions as a direct downstream component of D53 in regulating tiller number and SL-induced gene expression. We showed that D53 interacts with IPA1 in vivo and in vitro and suppresses the transcriptional activation activity of IPA1. We further showed that IPA1 could directly bind to the D53 promoter and plays a critical role in the feedback regulation of SL-induced D53 expression. These findings reveal that IPA1 is likely one of the long-speculated transcription factors that act with D53 to mediate the SL-regulated tiller development in rice.
獨腳金內酯(SLs)是一類類胡蘿卜素來源的萜類內酯，是一種通過抑制腋芽生長而抑制地上部分枝的植物激素。D53是SL信號通路的關鍵抑制因子，可能調控SL反應的下游轉錄網(wǎng)絡。然而，目前還沒有報道D53靶向的下游轉錄因子。本文報道了水稻理想株型基因IPA1作為D53的下游直接調控元件，調控水稻分蘗數(shù)和SL誘導的基因表達。我們發(fā)現(xiàn)D53在體內外均與IPA1相互作用，并抑制IPA1的轉錄激活活性。我們進一步證明，IPA1可以直接結合到D53啟動子上，并在SL誘導的D53表達的反饋調控中發(fā)揮關鍵作用。這些結果表明，IPA1可能是長期以來推測的與D53共同調控水稻分蘗發(fā)育的轉錄因子之一。