The phytohormone cytokinin plays a significant role in nearly all aspects of plant growth and development. Cytokinin signaling has primarily been studied in the dicot model Arabidopsis, with relatively little work done in monocots, which include rice (Oryza sativa) and other cereals of agronomic importance. The cytokinin signaling pathway is a phosphorelay comprised of the histidine kinase receptors, the authentic histidine phosphotransfer proteins (AHPs) and type‐B response regulators (RRs). Two negative regulators of cytokinin signaling have been identified: the type‐A RRs, which are cytokinin primary response genes, and the pseudo histidine phosphotransfer proteins (PHPs), which lack the His residue required for phosphorelay. Here, we describe the role of the rice PHP genes. Phylogenic analysis indicates that the PHPs are generally first found in the genomes of gymnosperms and that they arose independently in monocots and dicots. Consistent with this, the three rice PHPs fail to complement an Arabidopsis php mutant (aphp1/ahp6). Disruption of the three rice PHPs results in a molecular phenotype consistent with these elements acting as negative regulators of cytokinin signaling, including the induction of a number of type‐A RR and cytokinin oxidase genes. The triple php mutant affects multiple aspects of rice growth and development, including shoot morphology, panicle architecture, and seed fill. In contrast to Arabidopsis, disruption of the rice PHPs does not affect root vascular patterning, suggesting that while many aspects of key signaling networks are conserved between monocots and dicots, the roles of at least some cytokinin signaling elements are distinct.

中文翻译：

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假磷酸转移蛋白的功能在水稻和拟南芥之间存在差异

植物激素细胞分裂素在植物生长和发育的几乎所有方面都起着重要作用。细胞分裂素信号传导主要在双子叶植物模型拟南芥中进行研究，在单子叶植物中进行的工作相对较少，其中包括水稻 ( Oryza sativa ) 和其他具有重要农艺意义的谷物。细胞分裂素信号通路是由组氨酸激酶受体、真正的组氨酸磷酸转移蛋白 (AHP) 和 B 型反应调节剂 (RR) 组成的磷酸中继。已经确定了细胞分裂素信号传导的两个负调节因子：A 型 RRs，它是细胞分裂素初级反应基因，以及假组氨酸磷酸转移蛋白 (PHPs)，缺乏磷酸传递所需的 His 残基。在这里，我们描述一下大米PHP的作用基因。系统发育分析表明，PHPs 通常首先在裸子植物的基因组中发现，并且它们在单子叶植物和双子叶植物中独立出现。与此一致，三个水稻PHP未能补充拟南芥php突变体 ( aphp1/ahp6 )。三种水稻PHP 的破坏导致分子表型与这些作为细胞分裂素信号传导负调节因子的元素一致，包括诱导许多 A 型 RR 和细胞分裂素氧化酶基因。三重php突变体影响水稻生长发育的多个方面，包括枝条形态、穗结构和种子填充。与拟南芥相比，水稻PHP 的破坏 不影响根维管模式，这表明虽然单子叶植物和双子叶植物之间关键信号网络的许多方面都是保守的，但至少一些细胞分裂素信号元件的作用是不同的。