Mutation of chloroplast CHLM contributes to down-regulation of multiple stress response genes in Arabidopsis
Mutation of chloroplast CHLM contributes to down-regulation of multiple stress response genes in Arabidopsis
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DOI：
10.1007/s10725-020-00600-9
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发表时间：
2020-04-03
影响因子：
4.2
通讯作者：
Xiao, Lang-Tao
中科院分区：
文献类型：
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作者：
Huang, Chao;David, Molly P.;Xiao, Lang-Tao
Mg-原卟啉IX甲基转移酶（CHLM）在叶绿素生物合成中起关键作用，并将Mg-原卟啉IX转化为Mg-原卟啉IX单甲酯。先前的研究表明，CHLM的低表达导致拟南芥植物的淡绿色表型和Mg-原卟啉IX的积累。在此，我们报道了一种新的错义突变（G到A的转换），导致拟南芥chlm-4突变体中相应蛋白的Gly（59）→ Glu氨基酸替换。计算机模拟研究表明，这种取代可能会破坏CHLM的膜缔合。功能研究表明，突变形式的CHLM导致超氧阴离子自由基（O2-）的过度积累，虽然消除O2-可以减轻在chlm-4中观察到的黄色表型。此外，qRT-PCR和蛋白质印迹分析表明，O2-清除剂，FSD 1和CSD 2，在chlm-4植物的表达受到抑制。由于CHLM突变，光系统II蛋白的积累也减少。此外，我们发现，chlm-4植物表现出超敏感的盐胁迫在种子萌发和盐胁迫响应CBFs家族基因的表达下调。这些结果表明，CHLM正调控多个光合相关和胁迫反应的核基因的表达。
Mg-protoporphyrin IX methyltransferase (CHLM) plays a crucial role in chlorophyll biosynthesis and converts Mg-protoporphyrin IX to Mg-protoporphyrin IX monomethyl ester. Previous research has indicated that down-expression of CHLM causes a pale green phenotype and Mg-protoporphyrin IX accumulation in Arabidopsis thaliana plants. Here, we report that a novel missense mutation (G to A transition) in the CHLM gene, results in the Gly(59) -> Glu amino acid substitution in the corresponding protein of Arabidopsis chlm-4 mutant plants. In silico modelling studies suggested that this substitution may disrupt membrane association of CHLM. Functional studies showed that the mutant form of CHLM leads to the excessive accumulation of superoxide anion radicals (O2-), although elimination of O2- could alleviate the yellow phenotype observed in chlm-4. In addition, qRT-PCR and western blotting analysis demonstrated that the expression of O2- scavengers, FSD1 and CSD2, were repressed in chlm-4 plants. The accumulation of photosystem II proteins was also decreased due to the CHLM mutation. Furthermore, we found that chlm-4 plants exhibited hypersensitive salt-stress during seed germination and down-expression of the salt stress-responsive CBFs-family genes. These results suggest CHLM positively regulates the expression of multiple photosynthetic-related and stress-responsive nuclear genes.