Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
Plant Physiol. 2012 Apr;158(4):1666-84. doi: 10.1104/pp.111.192765. Epub 2012 Mar 1.
Two-component signaling elements play important roles in plants, including a central role in cytokinin signaling. We characterized two-component elements from the monocot rice (Oryza sativa) using several complementary approaches. Phylogenetic analysis reveals relatively simple orthologous relationships among the histidine kinases in rice and Arabidopsis (Arabidopsis thaliana). In contrast, the histidine-containing phosphotransfer proteins (OsHPs) and response regulators (OsRRs) display a higher degree of lineage-specific expansion. The intracellular localizations of several OsHPs and OsRRs were examined in rice and generally found to correspond to the localizations of their dicot counterparts. The functionality of rice type-B OsRRs was tested in Arabidopsis; one from a clade composed of both monocot and dicot type-B OsRRs complemented an Arabidopsis type-B response regulator mutant, but a type-B OsRR from a monocot-specific subfamily generally did not. The expression of genes encoding two-component elements and proteins involved in cytokinin biosynthesis and degradation was analyzed in rice roots and shoots and in response to phytohormones. Nearly all type-A OsRRs and OsHK4 were up-regulated in response to cytokinin, but other cytokinin signaling elements were not appreciably affected. Furthermore, multiple cytokinin oxidase (OsCKX) genes were up-regulated by cytokinin. Abscisic acid treatment decreased the expression of several genes involved in cytokinin biosynthesis and degradation. Auxin affected the expression of a few genes; brassinosteroid and gibberellin had only modest effects. Our results support a shared role for two-component elements in mediating cytokinin signaling in monocots and dicots and reveal how phytohormones can impact cytokinin function through modulating gene expression.
双组分信号元件在植物中起着重要作用，包括在细胞分裂素信号转导中起核心作用。我们使用几种互补方法从单子叶植物水稻（Oryza sativa）中鉴定了双组分元件。系统发育分析揭示了水稻和拟南芥（Arabidopsis thaliana）中的组氨酸激酶之间相对简单的直系同源关系。相比之下，组氨酸含有磷酸转移蛋白（OsHPs）和应答调节子（OsRRs）显示出更高程度的谱系特异性扩展。在水稻中检测了几种 OsHP 和 OsRR 的细胞内定位，通常发现它们与双子叶植物的对应物的定位相对应。在拟南芥中测试了水稻的类型-B OsRR 的功能；来自由单子叶和双子叶类型-B OsRR 组成的类群的一个补充了拟南芥类型-B 应答调节子突变体，但来自单子叶植物特有的亚家族的类型-B OsRR 通常没有。分析了编码双组分元件和参与细胞分裂素生物合成和降解的蛋白质的基因在水稻根和地上部分的表达，并对植物激素作出响应。几乎所有的类型-A OsRR 和 OsHK4 都对细胞分裂素的响应而上调，但其他细胞分裂素信号元件没有明显影响。此外，多个细胞分裂素氧化酶（OsCKX）基因被细胞分裂素上调。脱落酸处理降低了参与细胞分裂素生物合成和降解的几个基因的表达。生长素影响了少数基因的表达；油菜素内酯和赤霉素只有适度的影响。我们的结果支持双组分元件在介导单子叶植物和双子叶植物细胞分裂素信号中的共同作用，并揭示了植物激素如何通过调节基因表达来影响细胞分裂素的功能。
