论文题目：AtHSP90.5 and AtFtsH12 synergistically regulate the accumulation of photosynthesis protein complexes and chloroplast development in Arabidopsis
论文作者：Xiaomin Wang (王晓敏), Jiahui Zhong (钟家辉), Bilang Li (李碧浪), Shuo Yang (杨硕), Peiyi Wang (王佩仪), Jingxia Shao (邵景侠), Jingjing Meng (孟晶晶), Xiayan Liu (刘夏燕), Fei Yu (郁飞), Yafei Qi (齐亚飞)
论文摘要：The 90-kDa heat shock protein (HSP90) is a central component of the chaperone system for protein homeostasis (proteostasis). In Arabidopsis , AtHSP90.5 is the sole chloroplast-localized HSP90 family member, yet its role in chloroplast proteostasis remains poorly characterized. Here, we identify and characterize the pale green arabidopsis 5 mutant, pga5-1 , which exhibits defective chloroplast development and impaired accumulation of photosynthetic protein complexes. Genetic analysis revealed that pga5-1 is a hypomorphic allele of AtHSP90.5 , harboring a missense mutation (G646E) localized closely to the substrate-binding site. Biochemical studies demonstrated that AtHSP90.5 interacts with AtFtsH12, and the ATPase activity of AtHSP90.5 is essential for the oligomerization of AtFtsH12 complexes. Strikingly, the mutation of the conserved residue (E106A) for the ATPase activity of AtHSP90.5 can rescue the embryonic lethality of AtHSP90.5 null mutants, yielding albino seedlings with non-photosynthetic plastids, and partially complement pga5-1 . Furthermore, we show that AtHSP90.5 associates with subunits of light-harvesting antenna complexes, including LhcB1, LhcB2 and, LhcA1, and is epistatic to PGA4/cpSRP54 in regulating the accumulation of a chimeric chloroplast marker protein, LhcB2-GFP. Collectively, our findings establish a critical role for AtHSP90.5 in maintaining photosynthesis protein complexes and uncover a previously unknown functional link between AtHSP90.5 and AtFtsH12 in chloroplast protein translocation.
90kDa热休克蛋白(HSP90)是蛋白质稳态分子伴侣系统的核心组成部分。AtHSP90.5是拟南芥唯一的叶绿体定位HSP90家族成员，但其在叶绿体蛋白稳态中的作用仍未得到充分研究。该研究鉴定了拟南芥淡绿色突变体 pga5-1 ，该突变体表现出叶绿体发育缺陷和光合蛋白复合体的积累受损。遗传分析显示， pga5-1 是AtHSP90.5的一个亚效等位基因突变体，在底物结合位置附近存在一个错义突变（G646E）。生化研究表明AtHSP90.5与AtFtsH12相互作用，AtHSP90.5的ATP酶活性对AtFtsH12复合体的寡聚化至关重要。AtHSP90.5的ATP酶活性保守残基（E106A）突变可以拯救AtHSP90.5缺失突变体的胚胎致死，产生含有无色素的非光合质体的白化幼苗，并能够部分回补 pga5-1 。此外，该研究还发现AtHSP90.5与光捕获天线复合体的亚基互作，包括LhcB1、LhcB2和LhcA1，并且在调节叶绿体标记蛋白LhcB2-GFP的积累方面对PGA4/cpSRP54具有遗传上位效应。总之，该研究建立了AtHSP90.5在维持光合蛋白复合体中的关键作用，并揭示了AtHSP90.5与AtFtsH12相互作用调控叶绿体蛋白稳态的新功能。
论文链接：https://onlinelibrary.wiley.com/doi/10.1111/tpj.70369