LSES1, Encoding a Member of the Casein Kinase 1 Family, Is Involved in the Regulation of Leaf Senescence in Rice

The normal metabolism of transient starch in leaves plays a vital role in determining photosynthesis and final crop yield. However, the molecular mechanisms linking abnormal transient starch metabolism to premature leaf senescence remain unclear. Here, we isolate a rice mutant, lses1, with leaf yellowing and premature senescence, as well as excessive accumulation of starch granules in chloroplasts. Genetic analysis revealed that this trait is controlled by a single recessive nuclear gene. Through BSA-seq preliminary gene mapping, map-based cloning, and sequencing alignment, the candidate gene was pinpointed to LOC_Os02g40860 on chromosome 2, which encodes OsCKI1, a casein kinase I family member. The identity of LSES1 was confirmed functionally: genetic complementation with the native genomic sequence rescued the wild-type phenotype, while CRISPR/Cas9 knockout of the gene in wild-type plants recapitulated the premature senescence. This confirmed that LSES1/OsCKI1 is involved in the regulation of leaf senescence. Notably, one improved knockout line, KO-2, displayed significant agronomic improvements in grain length, grain width, number of productive ears, and number of filled grains per panicle, along with a significant increase in grain yield per plant, highlighting its potential breeding value. Subcellular localization and tissue-specific expression analysis showed that LSES1 is primarily nuclear-localized and constitutively expressed.