Department of Plant Genetics, Breeding and Biotechnology, Faculty of Horticulture and Landscape Architecture, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, Warsaw, 02-776, Poland.
Department of Botany, Faculty of Agriculture and Biology, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, Warsaw, 02-776, Poland.
Mol Plant. 2014 Jul;7(7):1151-66. doi: 10.1093/mp/ssu060. Epub 2014 May 29.
Mitogen-activated protein kinase (MAPK) pathways regulate signal transduction from different cellular compartments and from the extracellular environment to the nucleus in all eukaryotes. One of the best-characterized MAPKs in Arabidopsis thaliana is MPK4, which was shown to be a negative regulator of systemic-acquired resistance. The mpk4 mutant accumulates salicylic acid (SA), possesses constitutive expression of pathogenesis-related (PR) genes, and has an extremely dwarf phenotype. We show that suppression of SA and phylloquinone synthesis in chloroplasts by knocking down the ICS1 gene (by crossing it with the ics1 mutant) in the mpk4 mutant background did not revert mpk4-impaired growth. However, it did cause changes in the photosynthetic apparatus and severely impaired the quantum yield of photosystem II. Transmission microscopy analysis revealed that the chloroplasts' structure was strongly altered in the mpk4 and mpk4/ics1 double mutant. Analysis of reactive oxygen species (ROS)-scavenging enzymes expression showed that suppression of SA and phylloquinone synthesis in the chloroplasts of the mpk4 mutant caused imbalances in ROS homeostasis which were more pronounced in mpk4/ics1 than in mpk4. Taken together, the presented results strongly suggest that MPK4 is an ROS/hormonal rheostat hub that negatively, in an SA-dependent manner, regulates immune defenses, but at the same time positively regulates photosynthesis, ROS metabolism, and growth. Therefore, we concluded that MPK4 is a complex regulator of chloroplastic retrograde signaling for photosynthesis, growth, and immune defenses in Arabidopsis.
丝裂原活化蛋白激酶 (MAPK) 途径调节信号转导，从不同的细胞区室和细胞外环境传递到真核生物的细胞核。拟南芥中研究最透彻的 MAPK 之一是 MPK4，它被证明是系统获得性抗性的负调节剂。mpk4 突变体积累水杨酸 (SA)，组成型表达病程相关 (PR) 基因，表现出极度矮小的表型。我们表明，在 mpk4 突变体背景下通过敲低 ICS1 基因（与 ics1 突变体杂交）抑制叶绿体中的 SA 和叶绿醌合成并不能使 mpk4 受损的生长恢复正常。然而，它确实导致了光合作用装置的变化，并严重损害了光系统 II 的量子产量。透射电子显微镜分析显示，mpk4 和 mpk4/ics1 双突变体中的叶绿体结构发生了强烈改变。对活性氧 (ROS) 清除酶表达的分析表明，在 mpk4 突变体的叶绿体中抑制 SA 和叶绿醌合成导致 ROS 动态平衡失衡，在 mpk4/ics1 中比在 mpk4 中更为明显。综上所述，研究结果表明，MPK4 是 ROS/激素变阻器的枢纽，以依赖于 SA 的方式负调控免疫防御，但同时正调控光合作用、ROS 代谢和生长。因此，我们得出结论，MPK4 是拟南芥中叶绿体逆行信号转导对于光合作用、生长和免疫防御的复杂调节剂。
