School of Biosciences, University of Birmingham, Edgbaston, B15 2TT, UK.
Plant Sciences Department, Rothamsted Research, Harpenden, AL5 2JQ, UK.
Nat Commun. 2021 Jan 11;12(1):251. doi: 10.1038/s41467-020-20506-4.
Chloroplast function requires the coordinated action of nuclear- and chloroplast-derived proteins, including several hundred nuclear-encoded pentatricopeptide repeat (PPR) proteins that regulate plastid mRNA metabolism. Despite their large number and importance, regulatory mechanisms controlling PPR expression are poorly understood. Here we show that the Arabidopsis NOT4A ubiquitin-ligase positively regulates the expression of PROTON GRADIENT REGULATION 3 (PGR3), a PPR protein required for translating several thylakoid-localised photosynthetic components and ribosome subunits within chloroplasts. Loss of NOT4A function leads to a strong depletion of cytochrome bf and NAD(P)H dehydrogenase (NDH) complexes, as well as plastid 30 S ribosomes, which reduces mRNA translation and photosynthetic capacity, causing pale-yellow and slow-growth phenotypes. Quantitative transcriptome and proteome analysis of the not4a mutant reveal it lacks PGR3 expression, and that its molecular defects resemble those of a pgr3 mutant. Furthermore, we show that normal plastid function is restored to not4a through transgenic PGR3 expression. Our work identifies NOT4A as crucial for ensuring robust photosynthetic function during development and stress-response, through promoting PGR3 production and chloroplast translation.
叶绿体的功能需要核基因和叶绿体基因编码蛋白的协调作用，包括几百种调节质体 mRNA 代谢的核编码五肽重复（PPR）蛋白。尽管它们数量众多且非常重要，但控制 PPR 表达的调节机制仍知之甚少。本文中，我们发现拟南芥 NOT4A 泛素连接酶正向调控 PGR3 的表达，PGR3 是一种 PPR 蛋白，对于翻译几个定位于类囊体的光合作用组件和叶绿体中的核糖体亚基是必需的。NOT4A 功能丧失会导致细胞色素 bf 和 NAD(P)H 脱氢酶（NDH）复合物以及质体 30S 核糖体大量耗竭，从而降低 mRNA 翻译和光合作用能力，导致叶片呈浅黄色、生长缓慢。not4a 突变体的定量转录组和蛋白质组分析显示其缺乏 PGR3 的表达，并且其分子缺陷与 pgr3 突变体相似。此外，我们发现通过转基因 PGR3 表达可以将正常的质体功能恢复到 not4a 中。我们的工作表明，NOT4A 通过促进 PGR3 的产生和叶绿体翻译，对于确保发育和应激反应期间强大的光合作用功能至关重要。
