遗传发育所在激素调控水稻冠根发育研究获新成果

摘要 : 中国科学院遗传与发育生物学研究所植物基因组学国家重点实验室储成才课题组,通过大规模筛选水稻T-DNA插入突变体库，获得一个水稻根数目显著增加突变体，分子生物学及遗传学研究表明，该表型是由于编码另外一个细胞分裂素氧化酶/脱氢酶基因OsCKX4的激活而导致。该研究成果于5月7日在线发表于Plant Physiology杂志。储成才课题组博士后高少培博士和方军副研究员为该文章的共同第一作者。

细胞分裂素是植物中五大激素之一，在植物的生长发育上起着非常重要的作用。中国科学院遗传与发育生物学研究所植物基因组学国家重点实验室储成才课题组,通过大规模筛选水稻T-DNA插入突变体库，获得一个水稻根数目显著增加突变体，分子生物学及遗传学研究表明，该表型是由于编码另外一个细胞分裂素氧化酶/脱氢酶基因OsCKX4的激活而导致。该研究成果于5月7日在线发表于Plant Physiology杂志。储成才课题组博士后高少培博士和方军副研究员为该文章的共同第一作者。

据了解，许多高产水稻品种中一个编码细胞分裂素氧化酶/脱氢酶基因OsCKX2的突变，造成细胞分裂素在花序分生组织中的特异性累积，导致大穗的表型,最终导致水稻产量的大幅度提高。OsCKX4受植物激素细胞分裂素和生长素的快速诱导,并在主根及冠根起始部位有较高表达。研究进一步发现，OsCKX4通过整合植物细胞分裂素和生长素两种激素信号途径调控冠根起始。与OsCKX2在地上部分调控水稻穗粒数相对应，该项工作揭示细胞分裂素氧化酶不仅对水稻穗发育有重要作用，通过不同的细胞分裂素氧化酶/脱氢酶对植物地下根器官的发生也有很大的决定作用。这项研究成果不仅大大丰富了人们对细胞分裂素这一经典的植物激素在植物生长发育上的理解，也为水稻及其它植物通过“根工程”改良营养吸收及非生物胁迫耐受性提供了非常有潜力的靶标基因和思路。

原文摘要：

A cytokinin oxidase/dehydrogenase gene OsCKX4 integrates cytokinin and auxin signaling to control rice crown root formation

Shaopei Gao, Jun Fang, Fan Xu, Wei Wang, Xiaohong Sun, Jinfang Chu, Baodong Cai, Yuqi Feng and Chengcai Chu

Crown roots constitute the majority of the rice root system, and play an important role in rice growth and development. However, the molecular mechanism of crown root formation in rice is still not well understood. Here, we characterized a rice dominant mutant, root enhancer1 (ren1-D), which was observed to exhibit a more robust root system, increased crown root number, and reduced plant height. Molecular and genetic analyses revealed that these phenotypes are caused by the activation of a cytokinin oxidase/dehydrogenase (CKX) family gene, OsCKX4. Subcellular localization demonstrated that OsCKX4 is a cytosolic isoform of CKX. OsCKX4 is predominantly expressed in leaf blades and roots, and it is the dominant CKX preferentially expressed in the shoot base where crown root primordia are produced, underlining its role in root initiation. OsCKX4 is induced by exogenous auxin and cytokinin in the roots. Furthermore, one-hybrid assays revealed that OsCKX4 is a direct binding target of both auxin response factor OsARF25 and the cytokinin response regulators ORR2 and ORR3. Overexpression and RNAi of OsCKX4 confirmed that OsCKX4 plays a positive role in crown root formation. Moreover, expression analysis revealed a significant alteration in the expression of auxin-related genes in the ren1-D mutants, indicating that the OsCKX4 mediates crown root development by integrating the interaction between cytokinin and auxin. Transgenic plants harboring OsCKX4 under the control of a root-specific promoter RCc3 displayed enhanced root development without affecting their shoot parts, suggesting that this strategy could be a powerful tool in rice root engineering.

作者：吴昊

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