The Pentatricopeptide Repeat Protein OsPPR7 Confers Cold Tolerance at the Booting Stage in Rice by Regulating ABA and ROS Homeostasis

Cold stress at the booting stage severely disrupts pollen development and drastically reduces grain yield in rice. Uncovering the genetic basis of cold tolerance is essential for breeding resilient varieties. Here, we identified a cold‑sensitive mutant, csb1, from an EMS‑mutagenized population of the cold‑tolerant japonica variety MK1, which exhibits significantly impaired seed‑setting under cold stress. Genetic analysis indicated that the phenotype is controlled by a single recessive nuclear gene. Using MutMap, we mapped the causal locus to a 26.3-27.0 Mb interval on chromosome 8. Among candidate genes, OsPPR7, encoding a PLS‑class pentatricopeptide repeat (PPR) protein, showed strong cold‑induced expression in anthers. A promoter mutation in OsPPR7 was linked to the csb1 phenotype, as confirmed by genetic complementation. CRISPR/Cas9 knockout lines displayed increased cold sensitivity and severe pollen sterility, whereas overexpression enhanced tolerance. Cytological observations revealed that loss of OsPPR7 leads to defective anther development, abnormal pollen nuclei, and failed germination under cold stress. Mechanistically, OsPPR7, localized to mitochondria, regulates cold tolerance by fine‑tuning abscisic acid (ABA) biosynthesis and reactive oxygen species (ROS) homeostasis in young panicles. Haplotype analysis across diverse germplasm identified natural variation in OsPPR7, with the superior cold‑tolerant haplotype Hap_I showing strong selective sweep signals in temperate japonica rice, indicating its role in adaptation to high‑latitude environments. Our study identifies OsPPR7 as a novel positive regulator of reproductive stage cold tolerance and provides a valuable genetic target for improving rice climate resilience.