Molecular Mapping and Candidate Gene Analysis of a Yellow-Green Leaf 6 (ygl6) Mutant in Rice

A novel rice (Oryza sativa L.) mutant derived from the ethyl methane sulfonate-treated restorer line Jinhui10 was identified that exhibited stable inheritance and was tentatively named yellow-green leaf 6 (ygl6). Leaves of ygl6 were yellow-green at the seedling stage and pale green at the jointing stage. The contents of chlorophyll a, chlorophyll b, and carotenoids were significantly lower in the mutant than those in the wildtype (WT) at the seedling and heading stages. Leaf mesophyll cells of the ygl6 mutant and WT showed no obvious differences in ultrastructure. However, ygl6 chloroplasts developed abnormally with poorly developed thylakoids and fewer grana stacks. Genetic analysis demonstrated that the mutation was controlled by a single recessive gene. Genetic mapping of the mutant gene was conducted using 1997 recessive individuals from the F-2 segregating population. YGL6 was mapped to the centromeric region of chromosome 12 between the insertion/deletion primers Ind23 and Ind37, with an interval of 143 kb. Sequence analysis of the candidate genes within the delimited region showed a single base-pair change in Os12 g23180 that corresponded to a codon transition from leucine to a stop codon. Results of RNA interference knockdown of YGL6 suggested that Os12 g23180 is the candidate gene. Further characterization of YGL6 will provide insights into the molecular mechanisms of chloroplast development.