Monomerization of abscisic acid receptors through CARKs-mediated phosphorylation

 Abstarct 

背景+问题：Cytosolic ABA Receptor Kinases (CARKs) play a pivotal role in abscisic acid (ABA)-dependent pathway in response to dehydration, but their regulatory mechanism in ABA signaling remains unexplored. 

胞质ABA受体激酶CARKs在植物响应脱水胁迫时的ABA依赖途径中扮演关键作用，但是其在ABA信号转导中的分子调控机制仍不清晰。

结果1-功能冗余与分化：In this study, we showed that CARK4/5 of CARK family physically interacted with ABA receptors (RCARs/PYR1/PYLs), including RCAR3, RCAR11~RCAR14, while CARK2/7/11 only interacted with RCAR11~RCAR14, but not RCAR3. It indicates that the members in CARK family function redundantly and differentially in ABA signaling. 

本文中，作者发现CARK家族的CARK4/5能够与ABA受体RCARs/PYR1/PYLs中的RCAR3、RCAR11~RCAR14发生物理互作；而CARK2/7/11仅与RCAR11~RCAR14互作，不与RCAR3互作。该结果表明CARK家族的成员在ABA信号转导方面即存在功能冗余，也存在功能分化。

结果2-二聚化：RCAR12 can form heterodimer with RCAR3 in vitro and in vivo. Moreover, the members of CARK family can form homo- or heterodimer in a kinase activity dependent manner. 

RCAR12能够与RCAR3在体内和体外形成异源二聚体。此外，CARK家族的成员能够以激酶活性依赖的方式，形成同源或者异源的二聚体。

结果3-CARK介导的RCAR磷酸化促进其ABA结合亲和力：ITC (isothermal titration calorimetry) analysis demonstrated that the phosphorylation of RCAR12 by CARK1 enhanced the ABA binding affinity. The phosphor-mimic RCAR12^T105D significantly displayed ABA-induced inhibition of the phosphatase ABI1 (ABA insensitive 1) activity, leading to up-regulation of ABA-responsive genes RD29A and RD29B in cark157:RCAR12T105D transgenic plants, which exhibited ABA hypersensitive phenotype. 

等温滴定量热法分析显示，CARK1介导的RCAR12磷酸化增强了ABA的结合亲和力。通过RCAR12T105D模拟磷酸化，显著增强了cark157:RCAR12T105D转基因植株中由ABA诱导的ABI1磷酸酶活性抑制，从而导致ABA响应基因RD29A和RD29B的上调，因此表现出了ABA超敏表型。

结果4-ABI5促进CARK1/3：The transcription factor ABI5 (ABA insensitive 5) activates the transcriptions of CARK1 and CARK3 by binding to ABRE elements of their promoters. 

转录因子ABI5能够通过结合到CARK1和CARK3基因启动子上的ABRE元件，激活这两个基因的表达。

结论：Collectively, our data imply that the dimeric CARKs phosphorylate homo- or heterodimer ABA receptors, leading to monomerization for triggering ABA responses in Arabidopsis.

综上，本文的数据表明拟南芥中，二聚化的CARKs能够磷酸化ABA受体同源或异源二聚体，导致其单体化，从而诱导ABA的响应。

** 杨毅 **

doi: https://doi.org/10.1111/nph.18149

Journal: New Phytologist

​First Published: April 07, 2022