Fine mapping and identification of a novel albino gene OsAL50 that is required for chlorophyll biosynthesis and chloroplast development in rice (Oryza sativa L.)

Leaf color is a highly important agronomic trait, and mutants with altered leaf coloration can serve as excellent models for studies on chloroplast development and chlorophyll biosynthesis, enabling the cloning of genes involved in these processes in rice (Oryza sativa L.). In this study, we isolated a stable genetic rice mutant, oryza sativa albino leaf 50 (osal50), from a breeding population of the japonica cultivar GP50. This mutant exhibited a distinctive albino phenotype, with white-striped leaves in seedlings and white panicles at the heading stage. Compared with wild-type GP50, the osal50 mutant showed lower chlorophyll and carotenoid accumulation, together with abnormal chloroplast ultrastructure. Genetic analysis demonstrated that a recessive nuclear gene was responsible for the albino phenotype of osal50, and a map-based cloning strategy delimited OsAL50 to a 160-kb physical interval on chromosome 1, flanked by two single nucleotide polymorphism (SNP) markers, CAPS-08 and CAPS-37, that included 26 putative open reading frames. Sequence and expression analyses revealed LOC_Os01g20110 as the candidate OsAL50 gene, which was confirmed by knockout using CRISPR/Cas9. Subcellular localization and protein sequence analyses suggested that OsAL50 likely encodes an endoribonuclease E-like protein localized to the chloroplasts. Further investigation indicated that OsAL50 plays a vital role in the regulation of photosynthetic pigment metabolism, photosynthesis, and chloroplast biogenesis. In summary, we identified a novel albino mutant that will serve as useful genetic material for studies of chlorophyll biosynthesis and chloroplast development in rice.