Genetic analysis and fine-mapping of a new rice mutant, <Emphasis Type="Italic">white and lesion mimic leaf1</Emphasis>

Rice (Oryza sativa L.) leaf color mutants are excellent models for studying chlorophyll biosynthesis and chloroplast development. In this study, we isolated a stable genetic white and lesion mimic leaf1 (wlml1) mutant from an ethyl methanesulfonate (EMS)-mutagenized population of the indica cultivar TN1. Compared with wild-type TN1, the wlml1 mutant had lower contents of chlorophyll and carotenoids, altered chloroplast ultrastructure, and altered regulation of genes associated with chlorophyll metabolism and chloroplast development. In addition, lesions formed on the leaves of wlml1 plants grown at 20 °C and genes related to disease resistance and antioxidant functions were up-regulated; by contrast, the mutant phenotype was partially suppressed at 28 °C. These findings indicated that WLML1 might play a role in chlorophyll metabolism and chloroplast development, as well as in biotic and abiotic stress responses. Genetic analysis showed that WLML1 was controlled by a recessive nuclear gene, and map-based cloning delimited WLML1 to a 159.7-kb region on chromosome 4 that includes 30 putative open reading frames. Based on these findings, the wlml1 mutant will be a good genetic material for further studies on chlorophyll metabolism and stress responses in rice.