CP31A, a Rice Chloroplast Ribonucleoprotein Gene, Regulates Chloroplast mRNA Stability Conferring Drought and Cold Tolerance

Chloroplast ribonucleoproteins (cpRNPs) are nuclear-encoded and highly abundant proteins that are proposed to function in chloroplast RNA metabolism. However, the molecular mechanisms underlying the regulation of chloroplast RNAs involved in stress tolerance are poorly understood. Here, we demonstrate that OsCP31A, a rice (Oryza sativa) cpRNP gene, is essential for stabilization of RNAs from the NAD(P)H dehydrogenase (NDH) complex, which in turn enhances drought and cold stress tolerance. OsCP31A is expressed specifically in green tissues throughout all developmental stages, and the corresponding protein is localized in the chloroplasts. An RNA-immunoprecipitation assay revealed that OsCP31A is associated with a set of chloroplast RNAs. Transcript profiling indicated that the mRNA levels of genes from the NDH complex significantly increased in the OsCP31 overexpressing compared to non-transgenic plants, whereas the pattern in OsCP31 RNAi plants were opposite. The increase in mRNA stability of the NDH complex genes was verified by measuring the mRNA half-life during drought stress in the presence of the transcriptional inhibitor, cordycepin. Importantly, the OsCP31A overexpressing plants showed a higher cyclic electron transport (CET) activity, which is essential for elevated levels of ATP for photosynthesis, as well as plant fitness, under abiotic stress conditions. Additionally, overexpression of OsCP31A resulted in significantly enhanced drought and cold stress tolerance with higher ATP levels compared to wild type. Thus, our findings suggest that overexpression of OsCP31 stabilizes a set of mRNAs from genes of the NDH complex involved in increasing CET activity and production of ATP, which consequently confers enhanced drought and cold tolerance.