Role of Mg-chelatase on intracellular signal transduction

镁螯合酶由CHLI、CHLD和CHLH亚基组成，催化了叶绿素生物合成途径的第一步。在植物中，已知核编码光合作用相关基因的表达与叶绿体功能耦合。在拟南芥中，发现了称为gun（基因组解偶联）的突变体，其中细胞内信号传导被破坏。基因突变体的筛选表明，许多突变源于CHLH的错义突变，表明mg螯合酶不仅参与叶绿素合成，还参与胞内叶绿体向细胞核的信号转导（逆行信号转导）。在本研究中，我们构建了镁螯合酶活性的重构系统，揭示了枪的表型主要与镁螯合酶活性的抑制有关。然而，目前尚不清楚为什么这种抑制会导致体内CHLH蛋白的积累。对镁螯合酶复合物的功能和构象的分析将为植物细胞逆行信号通路的研究提供新的视角。

Mg-chelatase, which is composed by CHLI, CHLD, and CHLH subunits, catalyzes the the first committed step of chlorophyll biosynthetic pathway. In plants, it is known that the expression of nuclear-encoded photosynthesis related genes is coupled with chloroplast functionality. In Arabidopsis, mutants termed gun (genome uncoupled) were identified in which intracellular signaling was disrupted. Screening of gun mutants revealed many mutations were originated in mis-sense mutation of CHLH, suggesting Mg-chelatase functions not only for chlorophyll biosynthesis but also for the intracellular chloroplast to nucleus signal transduction (retrograde signaling).In this study, we have constructed reconstitution system of Mg-chelatase activity and revealed that gun phenotype is mainly related to the repression of Mg-chelatase activity. However, it is not clear why such repression caused the accumulation of CHLH protein in vivo. Analysis of functionality and conformation of Mg-chelatase complex will give novel insight into the retrograde signaling pathway in plant cells.