拟南芥PKS5激酶磷酸化ABI5参与植物ABA响应

PKS5 Kinase is Involved in ABA Response through Phosphorylating ABI5 in Arabidopsis

植物激素脱落酸（abscisic acid,ABA）在植物生长、发育及环境胁迫中起着重要的作用。本研究发现拟南芥PKSes（SOS2-like protein kinases）蛋白激酶家族成员PKS5（SOS2-like protein kinase 5）参与植物ABA响应。PKS5功能获得性点突变体pks5-3与pks5-4表现出对ABA的敏感表型。在外源ABA处理下,pks5-3与pks5-4种子萌发率降低,幼苗生长矮小、黄化。体外磷酸化测试显示,PKS5特异磷酸化ABA响应元件ABI5（ABA-insensitive 5）N末端多肽（1~211 aa）。q RT-PCR分析表明pks5-3与pks5-4突变体中ABI5下游ABA响应基因RAB18（RESPONSIVE TO ABA18）与EM6（LATE EMBRYOGENESIS ABUNDANT 6）表达均发生改变。这些研究结果表明,拟南芥PKS5通过磷酸化ABI5的N末端参与植物ABA响应过程。

The phytohormone abscisic acid（ABA） plays an essential role in plant growth and development as well as abiotic stress responses. In this study, we found that PKS5（SOS2-like protein kinase 5）, a family member of PKSes（SOS2-like protein kinases）, involved in ABA response in Arabidopsis. PKS5 gain-of-function point mutants pks5-3 and pks5-4 exhibited hypersensitive to ABA in the phenotypic test. Additionally, seed germinations of pks5-3 and pks5-4 decreased and seedlings of them showed stunted growth and leaf chlorotic symptoms under exogenous ABA treatment. In vitro phosphorylation assay indicated that PKS5 specifically phosphorylates the ABA-responsive component ABI5（ABA-insensitive 5） N terminus fragment range from 1 to 211 amino acids. Moreover, the relative expression levels of RAB18 and EM6, which are the downstream ABA-responsive genes of ABI5, significantly altered in pks5-3 and pks5-4 mutants compared with the wildtype plants by quantitative real-time PCR using gene-specific primers. Taken together, the results of this study revealed that PKS5 involves in ABA response via phosphorylating the N-terminus of ABI5 in Arabidopsis.