Liu Kaiwei, Lee Keun Pyo, Duan Jianli, Kim Eun Yu, Singh Rahul Mohan, Di Minghui, Meng Zhuoling, Kim Chanhong
Shanghai Center for Plant Stress Biology, Center for Excellence in Molecular Plant Sciences, Chinese Academy of Sciences, Shanghai, 200032, China.
University of the Chinese Academy of Sciences, Beijing, 100049, China.
Plant J. 2023 Apr;114(2):310-324. doi: 10.1111/tpj.16135. Epub 2023 Feb 26.
Chloroplast pre-ribosomal RNA (rRNA) undergoes maturation, which is critical for ribosome assembly. While the central and auxiliary factors in rRNA maturation have been elucidated in bacteria, their mode of action remains largely unexplored in chloroplasts. We now reveal chloroplast-specific factors involved in 16S rRNA maturation, Arabidopsis thaliana orthologs of bacterial RsmD methyltransferase (AtRsmD) and ribosome maturation factor RimM (AtRimM). A forward genetic screen aimed to find suppressors of the Arabidopsis yellow variegated 2 (var2) mutant defective in photosystem II quality control found a causal nonsense mutation in AtRsmD. The substantially impaired 16S rRNA maturation and translation due to the mutation rescued the leaf variegation phenotype by lowering the levels of chloroplast-encoded proteins, including photosystem II core proteins, in var2. The subsequent co-immunoprecipitation coupled with mass spectrometry analyses and bimolecular fluorescence complementation assay found that AtRsmD interacts with AtRimM. Consistent with their interaction, loss of AtRimM also considerably impairs 16S rRNA maturation with decelerated m G915 modification in 16S rRNA catalyzed by AtRsmD. The atrimM mutation also rescued var2 mutant phenotypes, corroborating the functional interplay between AtRsmD and AtRimM towards modification and maturation of 16S rRNA and chloroplast proteostasis. The maturation and post-transcriptional modifications of rRNA are critical to assembling ribosomes responsible for protein translation. Here, we revealed that the cooperative regulation of 16S rRNA m G915 modifications by AtRsmD methyltransferase and ribosome assembly factor AtRimM contributes to 16S rRNA maturation, ribosome assembly, and proteostasis in chloroplasts.
叶绿体前体核糖体RNA（rRNA）会经历成熟过程，这对核糖体组装至关重要。虽然细菌中rRNA成熟的核心和辅助因子已得到阐明，但其作用模式在叶绿体中仍 largely未被探索。我们现在揭示了参与16S rRNA成熟的叶绿体特异性因子，即细菌RsmD甲基转移酶（AtRsmD）和核糖体成熟因子RimM（AtRimM）的拟南芥直系同源物。一项旨在寻找在光系统II质量控制方面存在缺陷的拟南芥黄色斑驳2（var2）突变体抑制子的正向遗传筛选，在AtRsmD中发现了一个因果性无义突变。该突变导致的16S rRNA成熟和翻译严重受损，通过降低var2中叶绿体编码蛋白（包括光系统II核心蛋白）的水平，挽救了叶片斑驳表型。随后的免疫共沉淀结合质谱分析和双分子荧光互补试验发现，AtRsmD与AtRimM相互作用。与它们的相互作用一致，AtRimM的缺失也极大地损害了16S rRNA成熟，AtRsmD催化的16S rRNA中m G915修饰减速。atrimM突变也挽救了var2突变体表型，证实了AtRsmD和AtRimM在16S rRNA修饰和成熟以及叶绿体蛋白质稳态方面的功能相互作用。rRNA的成熟和转录后修饰对于组装负责蛋白质翻译的核糖体至关重要。在这里，我们揭示了AtRsmD甲基转移酶和核糖体组装因子AtRimM对16S rRNA m G915修饰的协同调控有助于叶绿体中的16S rRNA成熟、核糖体组装和蛋白质稳态。
