Site- and kinase-specific phosphorylation-mediated activation of SLAC1, a guard cell anion channel stimulated by abscisic acid
Site- and kinase-specific phosphorylation-mediated activation of SLAC1, a guard cell anion channel stimulated by abscisic acid
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DOI：
10.1126/scisignal.2005703
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发表时间：
2014-09-09
影响因子：
7.3
通讯作者：
Hedrich, Rainer
中科院分区：
文献类型：
--
作者：
Maierhofer, Tobias;Diekmann, Marion;Hedrich, Rainer
在干旱胁迫下，脱落酸（阿坝）触发称为气孔的叶细胞孔关闭，气孔由植物表皮中两个称为保卫细胞的特化细胞形成。阿坝下游的两条途径刺激S型阴离子通道SLAC 1（慢阴离子通道相关1）和SLAH 3（SLAC 1同系物3）的磷酸化，导致这些通道打开，减少保卫细胞体积并触发气孔关闭。一个分支涉及OST 1（开放气孔1），一种钙非依赖性SnRK 2型激酶，另一个分支涉及CPK（钙依赖性蛋白激酶）家族的钙依赖性蛋白激酶。我们在非洲爪蟾卵母细胞中进行共表达分析，结果表明钙调神经磷酸酶B样（CBL）钙传感器CBL 1和CBL 9及其相互作用的蛋白激酶CIPK 23也触发了SLAC 1和SLAH 3的开放。我们分析了这些不同家族的激酶调控SLAC 1开放是否涉及SLAC 1上相同或不同的位点，通过测量SLAC 1的通道电导，在氨基或羧基末端与非洲爪蟾卵母细胞中的特定激酶共表达的假定磷酸化位点发生突变。SLAC 1突变体缺乏OST 1磷酸化位点仍然激活CPK或CBL/CIPK复合物。磷酸化和激活SLAC 1的任何激酶抑制磷酸酶ABI 1（阿坝不敏感1），这是在响应阿坝信号失活。这些研究结果确定CBL/CIPK复合物作为气孔孔径通过S型阴离子通道的潜在调节剂，并表明在不同位点的磷酸化使SLAC 1通过阿坝下游的钙依赖性和钙非依赖性途径激活。
Under drought stress, abscisic acid (ABA) triggers closure of leaf cell pores called stomata, which are formed by two specialized cells called guard cells in plant epidermis. Two pathways downstream of ABA stimulate phosphorylation of the S-type anion channels SLAC1 (slow anion channel associated 1) and SLAH3 (SLAC1 homolog 3), which causes these channels to open, reducing guard cell volume and triggering stomatal closure. One branch involves OST1 (open stomata 1), a calcium-independent SnRK2-type kinase, and the other branch involves calcium-dependent protein kinases of the CPK (calcium-dependent protein kinase) family. We used coexpression analyses in Xenopus oocytes to show that the calcineurin B-like (CBL) calcium sensors CBL1 and CBL9 and their interacting protein kinase CIPK23 also triggered SLAC1 and SLAH3 opening. We analyzed whether regulation of SLAC1 opening by these different families of kinases involved the same or different sites on SLAC1 by measuring channel conductance of SLAC1 with mutations in the putative phosphorylation sites in the amino or carboxyl termini coexpressed with specific kinases in Xenopus oocytes. SLAC1 mutants lacking the OST1-phosphorylated site were still activated by CPK or by CBL/CIPK complexes. Phosphorylation and activation of SLAC1 by any of the kinases were inhibited by the phosphatase ABI1 (ABA insensitive 1), which is inactivated in response to ABA signaling. These findings identified CBL/CIPK complexes as potential regulators of stomatal aperture through S-type anion channels and indicated that phosphorylation at distinct sites enables SLAC1 activation by both calcium-dependent and calcium-independent pathways downstream of ABA.