RAS, a Pentatricopeptide Repeat Protein, Interacts with OsTRX z to Regulate Chloroplast Gene Transcription and RNA Processing.

Thioredoxin z (TRX z) plays a significant role in chloroplast development by regulating the transcription of chloroplast genes. In this study, we identified a pentatricopeptide repeat (PPR) protein, rice albino seedling-lethal (RAS), that interacts with OsTRX z. This interaction was initially discovered by using a yeast two-hybrid (Y2H) screening technique and was further validated through Y2H and bimolecular fluorescence complementation (BiFC) experiments. RAS contains 16 PPR motifs and features a small MutS-related (SMR) domain at its C-terminus. CRISPR/Cas9-generated mutants exhibited an albino seedling-lethal phenotype characterized by abnormal chloroplast structures and a significantly reduced chlorophyll content. RAS localizes to the chloroplast and is predominantly expressed in young leaves. Mutations in affect RNA editing at the , , and sites, as well as RNA splicing at the , , and transcripts within the chloroplast. Furthermore, the expression levels of genes associated with chloroplast formation are altered in the mutant. Both OsTRX z and RAS were found to interact with chloroplast signal recognition particle (cpSRP) proteins, indicating that their proper localization within the chloroplast may be dependent on the SRP pathway. Collectively, our findings highlight the critical role of RAS in chloroplast development, as it is involved in RNA processing and the regulation of chloroplast gene expression.