Suppressed OsPsbS1 expression triggers rice leaf senescence mediated by reactive oxygen species.

Premature leaf senescence is an important factor affecting rice growth, development, and fitness. Although rice photosystem II subunit S (OsPsbS1) is a major gene controlling nonphotochemical quenching capacity (NPQ) in the photoprotective process, the role it plays in rice leaf senescence has not been explored yet. In this study, we use CRISPR/Cas9 technology to edit the OsPsbS1 gene, resulting in stable homozygous lines with premature leaf senescence. The Ospsbs1 mutant lines have pale-yellow leaves, reduced chlorophyll content, and show accelerated chloroplast degradation. Reactive oxygen species, malondialdehyde, superoxide dismutase, and peroxidase activity were significantly increased in the mutants, whereas ascorbate peroxidase and catalase activity, as well as chlorophyll content and photosynthetic rate, were markedly decreased. Furthermore, they showed increased expression of genes involved in senescence, ROS, and chlorophyll degradation. The Ospsbs1 mutant plants were found to have severe DNA degradation and programmed cell death through TUNEL and staining, suggesting that excess ROS may cause leaf senescence. RNA sequencing analysis revealed that OsPsbS1 is involved in the regulation of multiple biological processes, such as glutathione (GSH), starch and sucrose, and nitrogen metabolism pathways. Our results demonstrate that disruption of OsPsbS1 can accelerate leaf senescence as a result of over-accumulation of ROS. The discovery of OsPsbS1's function in controlling leaf aging in rice provides further genetic insights for understanding the molecular pathways that govern premature leaf senescence.