水稻分蘖基因OsIAA16介导独脚金内酯与生长素互作的机理研究

Strigolactones (SLs) are a group of newly identified phytohormones that control plant shoot branching. The SLs biosynthesis and signal transduction pathway is currently one of the hotspots in the phytohormone research. Up to now, only a few genes have been identified in the SLs biosynthetic and signaling pathway. The underlying mechanism of cross-talks between SLs and auxin, another phytohormone.controlling shoot branching, also remains to be unveiled. We have isolated the OsIAA16 gene from the semi-dominant high-tillering dwarf rice mutant hd103 by a map-based cloning approach. Our preliminary studies have shown that OsIAA16 participates in the SLs signaling pathway. OsIAA16 is a member of the Aux/IAA gene superfamily, members of which are not only important repressors of auxin signaling but also mediators of the cross-talks between auxin and other hormones. However, the biological functions of OsIAA16 have not been reported. In this proposed project, physiological, biochemical and molecular approaches will be taken to elucidate how OsIAA16 works in the SLs and auxin signaling pathways and how it mediates the interaction between SLs and auxin. This research will improve our understanding of the SLs signal transduction pathway and establish a new model of the cross-talks between SLs and auxin. Objects of this study are tiller and root, both of which are important agronomic traits in rice production. Thus, this study has not only important theoretical significance, but also potential application value in the agricultural production.

独脚金内酯(SLs)是一种调控分枝的新型植物激素，其合成及信号传导途径是当今植物激素领域的研究热点之一。目前SLs途径中已发现的基因较少，其与另一种调控植物分枝的激素即生长素的互作机制亦无定论。本项目从水稻半显性矮化多分蘖突变体hd103中图位克隆了目标基因OsIAA16，并初步证明其处于SLs信号传导途径中。OsIAA16属于Aux/IAA基因家族，该家族成员不仅是生长素信号传导过程中的重要抑制因子，往往还介导生长素与其他植物激素的相互作用，但OsIAA16的生物学功能还未见报道。本研究将采用生理、生化和分子生物学等实验手段研究水稻OsIAA16在SLs和生长素途径中的作用，并探讨其在介导两种植物激素互作中的作用机制。本研究不仅可以完善SLs的信号传导途径，还可能发现SLs与生长素互作的新途径。本研究涉及水稻分蘖和根系等重要农艺性状，不仅具有重要理论意义，而且具有潜在应用价值。

生长素是调控植物分枝的重要激素，但其具体的分子调控机制以及与另一种调控植物分枝的激素独脚金内酯的相互作用机制仍不清楚。本项目筛选出1份水稻半显性矮化多分蘖突变体hd103，采用图位克隆技术克隆了目标基因OsIAA16。OsIAA16属于Aux/IAA基因家族，该家族成员是生长素信号传导过程中的重要抑制因子。在负责Aux/IAA蛋白降解的Degron motif发生了单碱基突变，导致突变后的OsIAA16蛋白稳定性增加。在hd103中采用RNA干扰技术(RNAi) 抑制IAA16的表达或者CRISPR-Cas9定点突变使IAA16失去功能时，hd103的株高及分蘖表型得到完全或部分恢复，说明hd103是由于体内IAA16功能获得性突变引起的。相比于野生型，hd103突变体根的生长和生长素响应标记基因DR5:GUS的表达对生长素的响应不敏感，说明hd103突变体在生长素的信号转导过程受阻。OsIAA16可以与生长素受体TIR1/AFB2以及11个生长素响应因子(ARF)家族成员相互作用，其中包括7个转录激活因子和4个转录抑制因子。RNAseq结果显示在hd103体内有大量上调及下调表达基因，其中两个WRKY家族转录因子表达量上升2000多倍。在后期的研究中，将围绕TIR1-IAA16-ARFs-WRKY的调控关系阐述生长素调控水稻分蘖数目的分子机理。独脚金内酯合成基因D10在hd103突变体中也表达上调，D10基因启动子区含有多个生长素响应元件AuxRE, 当将AuxRE元件缺失后，不能够互补d10突变体的矮化多分蘖表型，说明生长素对独脚金内酯的合成具有重要调控作用。

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