OST1 Activation by the Brassinosteroid-Regulated Kinase CDG1-Like 1 in Stomatal Closure

First author: Tae-Woo Kim; Affiliations: Hanyang University (汉阳大学): Seoul, Republic of Korea

Corresponding author: Tae-Wuk Kim

Crosstalk between signaling pathways is an important feature of complex regulatory networks. How signal crosstalk circuits are tailored (调整使适应) to suit different needs of various cell types remains a mystery in biology. Brassinosteroid (BR; 油菜素内酯) and abscisic acid (ABA) antagonistically (对抗性地) regulate many aspects of plant growth and development through direct interactions between components of the two signaling pathways. Here we show that BR and ABA synergistically (协同地) regulate stomatal closure through crosstalk between the BR-activated kinase CDG1-LIKE 1 (CDL1) and the OPEN STOMATA 1 (OST1) of the ABA signaling pathway in Arabidopsis thaliana. We demonstrate that the cdl1 mutant displayed reduced sensitivity to ABA in a stomatal closure assay, similar to the ost1 mutant. CDL1 and the BR receptor BR-INSENSITIVE 1 (BRI1), but not other downstream components of the BR signaling pathway, were required for BR regulation of stomatal movement. Genetic and biochemical experiments demonstrated that CDL1 activates OST1 by phosphorylating (磷酸化) it on residue Ser7. BR increased phosphorylation of OST1, and the BR-induced OST1 activation was abolished in cdl1 mutants. Moreover, we found that ABA activates CDL1 in an OST1-dependent manner. Taken together, our findings illustrate a cell-type specific BR signaling branch through which BR acts synergistically with ABA in regulating stomatal closure.

信号通路之间的交联是复杂调控网络中的一个重要特性。    信号之间的交联如何调整以适应不同细胞类型的复杂需求仍然是一个谜团。油菜素内脂BR与脱落酸ABA通过两个信号通路内的组分直接互作拮抗调控植物生长和发育的多个方面。本文的研究显示拟南芥中BR和ABA通过BR激活激酶CDL1与ABA信号通路中的OST1相互作用协同调控气孔关闭。cdl1突变体在气孔关闭试验中对于ABA的敏感度下降，与ost1突变体的表型类似。CDL1和BR受体BRI1，而非其余BR信号通路的下游组分，对于BR调控气孔运动是必需的。遗传和生化试验显示CDL1通过磷酸化OST1上的Ser7残基来激活OST1。BR增强了OST1的磷酸化程度，并且在cdl1突变体中BR诱导的OST1激活被阻碍。此外，作者还发现ABA以OST1依赖型的形式激活CDL1。综上，本文的研究阐释了一种细胞类型特异性BR信号分枝，BR通过与ABA协同互作，共同调控植物的气孔关闭。

doi: https://doi.org/10.1105/tpc.18.00239

Journal: Plant Cell

First Published: 31 July, 2018

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