Cold-sensitive chloroplast development: advances from chloroplast ribosome-deficient mutants

Cold-sensitive chloroplast ribosome-deficient mutants reveal that low temperature disrupts chloroplast ribosome biogenesis, chloroplast translation, and nascent polypeptide protection, thereby impairing chloroplast biogenesis and delaying chloroplast development in young leaves. In nature, cold stress commonly delays leaf greening in juvenile leaves of susceptible plant species. Accumulating evidence suggests that cold stress impairs chloroplast development, primarily by suppressing translational processes within chloroplasts, which play a pivotal role in their biogenesis. Although wild-type model plants exhibit no obvious delay in leaf greening under cold stress, numerous mutants defective in chloroplast translation display a cold-sensitive phenotype, characterized by markedly slowed greening of newly emerged leaves. Investigating these mutants provides valuable insights into the mechanisms underlying cold-sensitive chloroplast development, thereby offering potential strategies to improve chloroplast biogenesis in plants impaired by low-temperature conditions. This review summarizes recent advances in the analysis of chloroplast ribosome-defective mutants, which exhibit low-temperature-induced defects in early chloroplast development. These mutants have been classified into two categories based on their functional sites, including chloroplast ribosome biogenesis, and chloroplast translation and nascent polypeptide protection. We also summarize the mechanisms underlying the impact of low temperature on chloroplast development, as revealed through the study of chloroplast translation-defective mutants. Finally, based on current research findings, we propose strategies to protect the development of cold-sensitive chloroplasts and highlight the major unresolved questions and future directions in this field of study.