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.

中文翻译：

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IPA1在水稻的异丁内酯信号传导中作为D53抑制的下游转录因子。

Strigolactones（SLs）是一组类胡萝卜素衍生的萜内酯，是一种从根到茎的植物激素，可通过抑制腋芽的生长来抑制枝条分支。据推测，DWARF 53（D53）是SL信号通路的关键阻遏物，可调节SL反应的下游转录网络。然而，尚未报道D53靶向的下游转录因子。在这里，我们报告理想植物结构1（IPA1），水稻中植物结构的关键调节剂，在调节分number数和SL诱导的基因表达中起D53的直接下游成分的作用。我们显示D53在体内和体外与IPA1相互作用，并抑制IPA1的转录激活活性。我们进一步表明，IPA1可以直接结合D53启动子，并在SL诱导的D53表达的反馈调节中起关键作用。这些发现表明，IPA1可能是长期推测的转录因子之一，可与D53介导水稻中SL调控的分till发育。