SUMMARY Chloroplast ribosomal RNA (Ch‐rRNA) methylation is critical for plant development and response to low temperatures. Several Ch‐rRNA methyltransferases and their catalytic modes, as well as biological relevance, have been reported in model plant species. However, Ch‐rRNA methyltransferases and their functional significance remain poorly characterized in crops, including leafy vegetables such as Chinese cabbage. In this study, we screened an EMS‐mutagenized Chinese cabbage population and identified a yellow inner leaf ( yif ) mutant. This mutant develops yellowing inner leaves with reduced chlorophyll accumulation and ultrastructure‐impaired chloroplasts under low‐temperature conditions. Genetic analysis revealed a premature termination mutation in BrPFC1 , encoding the chloroplast‐localized 16S rRNA dimethyltransferase. The BrPFC1 mutation ( yif ) disrupts the dimethylation of 16S rRNA. The cold‐sensitive phenotype of the yif mutant can be explained by temperature‐dependent defects in the maturation and assembly of chloroplast ribosomes at 4°C. Through integrated analysis of chloroplast and nuclear transcriptomes coupled with translational profiling at 25°C and 4°C, we established that low temperature preferentially upregulates transcripts encoding nuclear‐derived ribosomal proteins, while defective 16S rRNA specifically compromises the translational efficiency of chloroplast‐encoded photosynthetic complex and ribosomal protein at 4°C. These findings establish rRNA modification by BrPFC1 as a critical regulatory layer for optimizing chloroplast translational efficiency at 4°C, providing mechanistic insights into post‐translational adaptation strategies in Chinese cabbage.
Liu et al. (Wed,) studied this question.