School of Life Sciences, Jawaharlal Nehru University, 415, New Delhi, 110067, India.
Plant Mol Biol. 2020 May;103(1-2):173-184. doi: 10.1007/s11103-020-00982-4. Epub 2020 Feb 25.
Arabidopsis LONG-CHAIN BASE KINASE 1 (LCBK1) interacts with MEDEA, a component of PCR2 complex that negatively regulates immunity. LCBK1 phosphorylates phytosphingosine and thereby promotes stomatal immunity against bacterial pathogens. Arabidopsis polycomb-group repressor complex2 (PRC2) protein MEDEA (MEA) suppresses both pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). MEA represses the expression of RPS2 and thereby attenuates AvrRpt2 effector-mediated ETI. However, the mechanism of MEA-mediated PTI diminution was not known. By screening the Arabidopsis cDNA library using yeast-2-hybrid interaction, we identified LONG-CHAIN BASE KINASE1 (LCBK1) as an MEA-interacting protein. We found that lcbk1 mutants are susceptible to virulent bacterial pathogens, such as Pseudomonas syringae pv maculicola (Psm) and P. syringae pv tomato (Pst) but not the avirulent strain of Pst that carries AvrRpt2 effector. Pathogen inoculation induces LCBK1 expression, especially in guard cells. We found that LCBK1 has a positive regulatory role in stomatal closure after pathogen inoculation. WT plants close stomata within an hour of Pst inoculation or flg22 (a 22 amino acid peptide from bacterial flagellin protein that activates PTI) treatment, but not lcbk1 mutants. LCBK1 phosphorylates phytosphingosine (PHS). Exogenous application of phosphorylated PHS (PHS-P) induces stomatal closure and rescues loss-of-PTI phenotype of lcbk1 mutant plants. MEA overexpressing (MEA-Oex) plants are defective, whereas loss-of-function mea-6 mutants are hyperactive in PTI-induced stomatal closure. Exogenous application of PHS-P rescues loss-of-PTI in MEA-Oex plants. Results altogether demonstrate that LCBK1 is an interactor of MEA that positively regulates PTI-induced stomatal closure in Arabidopsis.
拟南芥长链碱基激酶 1（LCBK1）与 MEDEA 相互作用，MEDEA 是 PCR2 复合物的一个组成部分，该复合物负调控免疫。LCBK1 磷酸化植物鞘氨醇，从而促进气孔对细菌病原体的免疫。拟南芥多梳组抑制复合物 2（PRC2）蛋白 MEDEA（MEA）抑制模式触发免疫（PTI）和效应物触发免疫（ETI）。MEA 抑制 RPS2 的表达，从而减弱 AvrRpt2 效应物介导的 ETI。然而，MEA 介导的 PTI 减弱的机制尚不清楚。通过酵母双杂交相互作用筛选拟南芥 cDNA 文库，我们鉴定出 LONG-CHAIN BASE KINASE1（LCBK1）是 MEA 的互作蛋白。我们发现 lcbk1 突变体易受毒性细菌病原体的侵袭，如丁香假单胞菌 pv 褐斑病（Psm）和丁香假单胞菌 pv 番茄（Pst），但不包括携带 AvrRpt2 效应物的无毒菌株 Pst。病原体接种诱导 LCBK1 的表达，尤其是在保卫细胞中。我们发现 LCBK1 在病原体接种后气孔关闭中具有正向调控作用。WT 植物在接种 Pst 或 flg22（一种来自细菌鞭毛蛋白的 22 个氨基酸肽，激活 PTI）处理后 1 小时内关闭气孔，但 lcbk1 突变体不关闭。LCBK1 磷酸化植物鞘氨醇（PHS）。外源性添加磷酸化 PHS（PHS-P）诱导气孔关闭，并挽救 lcbk1 突变体植物的 PTI 表型缺失。MEA 过表达（MEA-Oex）植物有缺陷，而功能丧失 mea-6 突变体在 PTI 诱导的气孔关闭中过度活跃。外源性添加 PHS-P 可挽救 MEA-Oex 植物的 PTI 缺失。结果表明，LCBK1 是 MEA 的一个互作蛋白，它正向调控拟南芥中 PTI 诱导的气孔关闭。
