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 Gly59 → 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.

中文翻译：

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叶绿体 CHLM 的突变有助于下调拟南芥中的多个应激反应基因

Mg-原卟啉 IX 甲基转移酶 (CHLM) 在叶绿素生物合成中起着至关重要的作用，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 的下调导致拟南芥植物中的淡绿色表型和镁原卟啉 IX 积累。在这里，我们报告了 CHLM 基因中的一个新的错义突变（G 到 A 转换），导致拟南芥 chlm-4 突变植物的相应蛋白质中的 Gly59 → Glu 氨基酸取代。计算机模拟研究表明，这种替代可能会破坏 CHLM 的膜结合。功能研究表明，CHLM 的突变形式导致超氧阴离子自由基 (O2-) 的过度积累，尽管消除 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 FSD1 和 CSD2 的表达在 chlm-4 植物中受到抑制。由于 CHLM 突变，光系统 II 蛋白的积累也减少了。此外，我们发现 chlm-4 植物在种子萌发和盐胁迫响应 CBFs 家族基因的下调过程中表现出过敏性盐胁迫。这些结果表明 CHLM 正向调节多个光合相关和应激反应核基因的表达。我们发现 chlm-4 植物在种子萌发和盐胁迫响应 CBFs 家族基因的下调过程中表现出对盐胁迫的敏感性。这些结果表明 CHLM 正向调节多个光合相关和应激反应核基因的表达。我们发现 chlm-4 植物在种子萌发和盐胁迫响应 CBFs 家族基因的下调过程中表现出对盐胁迫的敏感性。这些结果表明 CHLM 正向调节多个光合相关和应激反应核基因的表达。