Liu Zhenning, Yuan Li, Song Xiaoya, Yu Xiaolin, Sundaresan Venkatesan
College of Agriculture and Forestry Sciences, Linyi University, Linyi, Shandong 276000, China.
Department of Plant Biology, University of California, Davis, CA 95616, USA.
J Exp Bot. 2017 Jun 15;68(13):3365-3373. doi: 10.1093/jxb/erx181.
Histidine phosphotransfer proteins (HPs) are key elements of the two-component signaling system, which act as a shuttle to transfer phosphorylation signals from histidine kinases (HKs) to response regulators (RRs). CYTOKININ INDEPENDENT 1 (CKI1), a key regulator of central cell specification in the Arabidopsis female gametophyte, activates the cytokinin signaling pathway through the Arabidopsis histidine phosphotransfer proteins (AHPs). There are five HP genes in Arabidopsis, AHP1-AHP5, but it remains unknown which AHP genes act downstream of CKI1 in Arabidopsis female gametophyte development. Promoter activity analysis of AHP1-AHP5 in embryo sacs revealed AHP1, AHP2, AHP3, and AHP5 expression in the central cell. Phenotypic studies of various combinations of ahp mutants showed that triple mutations in AHP2, AHP3, and AHP5 resulted in defective embryo sac development. Using cell-specific single and double markers in the female gametophyte, the ahp2-2 ahp3 ahp5-2/+ triple mutant ovules showed loss of central cell and antipodal cell fates and gain of egg cell or synergid cell attributes, resembling the cki1 mutant phenotypes. These data suggest that AHP2, AHP3, and AHP5 are the major factors acting downstream of CKI1 in the two-component cytokinin signaling pathway to promote Arabidopsis female gametophyte development.
组氨酸磷酸转移蛋白（HPs）是双组分信号系统的关键元件，其作为一种穿梭蛋白，将磷酸化信号从组氨酸激酶（HKs）传递至响应调节因子（RRs）。细胞分裂素不依赖1（CKI1）是拟南芥雌配子体中央细胞特化的关键调节因子，它通过拟南芥组氨酸磷酸转移蛋白（AHPs）激活细胞分裂素信号通路。拟南芥中有五个HP基因，即AHP1 - AHP5，但在拟南芥雌配子体发育过程中，哪些AHP基因在CKI1下游发挥作用仍不清楚。对胚囊中AHP1 - AHP5的启动子活性分析显示，中央细胞中有AHP1、AHP2、AHP3和AHP5的表达。对ahp突变体各种组合的表型研究表明，AHP2、AHP3和AHP5的三重突变导致胚囊发育缺陷。利用雌配子体中细胞特异性的单标记和双标记，ahp2 - 2 ahp3 ahp5 - 2/+三重突变胚珠显示中央细胞和反足细胞命运丧失，卵细胞或助细胞属性增加，类似于cki1突变体表型。这些数据表明，AHP2、AHP3和AHP5是双组分细胞分裂素信号通路中在CKI1下游发挥作用以促进拟南芥雌配子体发育的主要因子。
