Abstract
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.
Highlights
Leaves are the main photosynthetic organs in plants, and changes in leaf color occur during growth and development, including increases in chlorophyll contents on de-etiolation and decreases in chlorophyll during senescence
We identified the wlml1 mutant, which has white and lesioned leaves and can be used as a marker in breeding to maintain the purity of varieties due to the minimal impact of the mutation on important agronomic traits in rice
Since the wlml1 mutation negatively affected chlorophyll metabolism and chloroplast development, this mutant will be useful for in-depth studies of chlorophyll metabolism and chloroplast development
Summary
Leaves are the main photosynthetic organs in plants, and changes in leaf color occur during growth and development, including increases in chlorophyll contents on de-etiolation and decreases in chlorophyll during senescence. Seven chlorophyll biosynthesis genes have been identified in rice: magnesium-chelatase ChlD subunit (OsCHLD), magnesiumchelatase ChlI subunit (OsCHLI), magnesium-chelatase ChlH subunit (OsCHLH), chlorophyll synthase (OsCHLG), divinyl reductase gene (OsDVR), protochlorophyllide oxidoreductase (OsPOR), and chlorophyll a oxygenase (OsCAO) (Nagata et al 2004). Mutations in these genes affect chlorophyll synthesis, resulting in changes in leaf color. Non-yellow coloring 1 (NYC1), which encodes a chlorophyll b reductase enzyme, results in an inhibition of chlorophyll b degradation, and a stay-green phenotype (Sato et al 2009)
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