Departments of Molecular Biology and Plant Biology, University of Geneva, Switzerland
Department of Biochemistry and Biophysics, University of California, San Francisco, CA, U.S.A.
Essays Biochem. 2018 Apr 13;62(1):13-20. doi: 10.1042/EBC20170048.
Although chloroplasts contain their own genetic system and are semi-autonomous cell organelles, plastid biogenesis and homeostasis are heavily dependent on the nucleo-cytosolic compartment. These two cellular compartments are closely co-ordinated through a complex signaling network comprising both anterograde and retrograde signaling chains. Developmental changes or any perturbation in the chloroplast system induced by a particular stress resulting from changes in environmental conditions such as excess light, elevated temperature, nutrient limitation, pathogen infection, give rise to specific signals. They migrate out of the chloroplast and are perceived by the nucleus where they elicit changes in expression of particular genes that allow for the maintenance of plastid homeostasis toward environmental cues. These genes mainly include those of photosynthesis-associated proteins, chaperones, proteases, nucleases and immune/defense proteins. Besides this transcriptional response, a chloroplast quality control system exists that is involved in the repair and turnover of damaged plastid proteins. This system degrades aggregated or damaged proteins and it can even remove entire chloroplasts when they have suffered heavy damage. This response comprises several processes such as plastid autophagy and ubiquitin-proteasome mediated proteolysis that occurs on the plastid envelope through the action of the ubiquitin-proteasome system.
虽然叶绿体含有自己的遗传系统和半自主的细胞器官，但质体的生物发生和动态平衡严重依赖于核质细胞区室。这两个细胞区室通过一个复杂的信号网络紧密协调，该网络包含前向和后向信号链。发育变化或由环境条件变化引起的叶绿体系统的任何干扰，如过量的光、高温、营养限制、病原体感染等，都会产生特定的信号。这些信号从叶绿体中迁移出来，并被细胞核感知，从而引发特定基因的表达变化，使质体能够根据环境线索维持动态平衡。这些基因主要包括与光合作用相关的蛋白、伴侣蛋白、蛋白酶、核酸酶和免疫/防御蛋白的基因。除了这种转录反应外，还存在一个质体质量控制系统，该系统参与受损质体蛋白的修复和周转。该系统降解聚集或受损的蛋白质，甚至可以在叶绿体受到严重损伤时将其全部清除。这种反应包括几种过程，如质体自噬和通过泛素-蛋白酶体系统在质体包膜上发生的泛素-蛋白酶体介导的蛋白水解。
