Abstract: A yellow-green leaf mutant ygl98 was isolated by chemistry mutagenesis. Its whole plant exhibited yellow-green trait throughout the growing period. Compared with its wild-type parent 10079, the contents of chlorophyll and carotenoid decreased by 45.3% and 45.6%; and at the maturity, the number of productive panicles per plant, seed setting rate and plant height reduced by 14.4%, 10.7%, and 7.4%, respectively. The result of electron microscopic observation revealed that the chloroplasts in the ygl98 mutant were out-of-shape. A lot of cystic structures and poor thylakoids were observed in the chloroplasts of the ygl98 mutant, and grana stacks appeared to be less dense compared to those of wild type. Genetic analysis showed that the yellow-green leaf trait of the ygl98 mutant was controlled by one pair of recessive nuclear genes. Genetic mapping of the mutant gene was conducted by using 771 yellow-green leaf individuals from the F₂ mapping population of ygl98/Zhefu 802. Finally, the mutant gene was mapped between InDel markers I3 and I4 on the long arm of chromosome 3, with genetic distances of 0.07 and 0.19 cM, respectively, and with physical distance of 44.2 kb, in which eight predicted genes had been annotated. Sequencing analysis of these candidate genes between the mutant and its wild-type revealed the single base change (G1522A) of the gene for magnesium-chelatase ChlD subunit resulted in a missense mutation (A508T) in the encoded product. The same gene mutation caused by OsChlD(Chlorina-1) was documented previously. The Chlorina-1 mutant displays a severe yellowish-green leaf phenotype only at the seedling stage, and the abnormal leaf color is ?rst observed on the leaves of 2- to 3-week-old seedlings, while the ygl98 mutant exhibits yellow-green trait throughout the growing period. The different phenotypes of the two mutants may be caused by the different mutational sites of OsChlD genomic sequence.

Key words: Oryza sativa L., Yellow-green leaf mutant, OsChlD, Genetic analysis, Fine-mapping