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Leaf‐color mutants have been extensively studied in rice (Oryza sativa L.) and many corresponding genes have been identified and cloned. However, the mechanism of complex leaf‐color mutations requires further study. In this study, we obtained an introgression line (TIL22) from a set of introgression lines raised using African cultivated rice (O. glaberrima Steud.) as the donor parent and O. sativa subsp. indica Teqing as the recipient. Compared with Teqing, TIL22 showed a yellow‐green leaf phenotype at the seedling stage, but the leaves gradually changed to green after the five‐leaf stage. The photosynthetic pigment contents of yellow‐green leaves at the seedling stage were significantly reduced and chloroplast development was retarded compared with those of Teqing. Genetic analysis indicated that the introgression line phenotype was controlled by a single nuclear gene, temporarily designated YGL22. Map‐based cloning and sequence analysis suggested that the candidate gene was likely to be LOC_Os01g15390, which encodes a chloroplast protein. Real‐time quantitative polymerase chain reaction (qPCR) analysis revealed that the YGL22 transcript level was significantly lower in TIL22 than that of Teqing at the seedling stage. We generated the ygl22 knockout mutant using the CRISPR/Cas9 system. The ygl22 mutants showed a similar phenotype to that of TIL22 at the seedling stage, suggesting that YGL22 may be involved in the early development of chloroplasts in rice. In addition, plant height, number of panicles per plant, and grain yield per plant of ygl22 were not significantly affected. The results indicate that YGL22 can be used as a trait marker gene in hybrid rice production. [ABSTRACT FROM AUTHOR]