Genetic Identification Of Five Leaf-color Mutants In Rice

The leaf color mutants are important materials for rice functional genomics research, and the leaf color could also be applicable as a specific marker character in the rice production. In the present study, we isolated five leaf-color mutants,507ys, 522ys,530ys, ygl80 and zebra524, from ethyl methanesulfonate (EMS) mutagenesis. At the same time, we also conduct genetic identification of these mutants. The results are as follows:Three yellow-green leaf mutants (507ys,522ys and 530ys) were screened from an ethyl methanesulfonate (EMS)-mutagenized population of rice ’Nipponbare, NP’. Under field conditions, whole plants of the three mutants exhibited yellow-green trait throughout the growing period. Compared to NP, the average contents of plant height, number of productive panicles per plant, number of spikelets per panicle, seed setting rate and 1000-grain weight were reduced by 10.4%,28.0%,8.8%,9.1% and 16.3%. HPLC analysis of chlorophyll composition in leaves indicated mutants accumulated only chlorophyll a and no chlorophyll b, at seedling. The phenotypes of the three mutants are controlled by a single recessive nuclear gene in each. We fine-mapped 507ys gene on chromosome 10,60.2-kb region flanked by RM333 and Indel mark L3. We performed rough mapping of 522ys using SSR markers, the 522ys locus was mapped between the markers RM333 and RM4771 within 0.64 cM and 3.16 cM on chromosome 10. And 530ys locus was rough mapped between RM333 and RM4771 within 0.52 cM and 2.59 cM on chromosome 10.507ys,522ys and 530ys were crossed with each other using all possible cross-combinations. F1 populations derived from the crosses exhibited a yellow-green phenotype. Sequencing analysis of OsCAO1 which encode chlorophyllide a oxygenase revealed a single base change (G to A) in the exon of 507ys (the seventh exon) and 522ys (the sixth exon), in the intron of 530ys (the first intron). It is possible to occur the mutation into the intron splicing site of 530ys. The results indicated that the genes conferring the yellow-green phenotype in 507ys,522ys and 530ys were allelic.A yellow-green leaf mutant ygl80 was isolated by chemical mutagenesis. Compared with the wild-type parent 10079, chlorophyll content of the ygl80 mutant decreased by 76.64% and 54.59%, and the carotenoid content decreased by 53.85% and 41.18% at the seedling and booting stages, respectively. In addition, plant height, number of productive panicles per plant, number of spikelets per panicle, panicle length and 1000-grain weight reduced by 14.8%,16.5%,21.3%,9.1%, and 7.4%, respectively, at the maturity. In a previous study, the mutant gene was mapped on chromosome 5,90-kb region flanked by C2 and C3. In this region eleven predicted genes had been annotated. Sequencing analysis of these candidate genes between the mutant and its wild-type parent revealed a single base change (C5027T) of YGL1(LOC_Os05g28200) gene for chlorophyll synthase resulted in a missense mutation (P348L) in the encoded product, suggesting that the ygl80 mutant gene is allelic to the ygll gene.A zedra leaf mutant, designated as zebra524, was isolated from an ethyl methanesulfonate (EMS)-mutagenized population. During seedling and tillering stages, the zebra524 mutant showed alternating transverse pale green and albino sectors on leaves. During booting stage, its albino sectors turned into pale green and the newly grown leaves became completely pale green. The zebra524 mutant also showed pale glumes during heading and grain-filling stages, and brown nodes, pink basal internodes, orange-red embryos and basal caryopsises at maturation stage. In addition, plumules of zebra524 showed an orange-red color in the dark. Chlorophyll contents in leaves of the zebra524 mutant decreased by 82.8% and 20.9%, and carotenoid contents decreased by 64.7% and 32.6% at seedling and booting stages, respectively, compared with those of the wild type. In addition, the levels of chlorophylls and carotenoids in glumes of zebra524 mutant were reduced by 38.1% and 42.8%, respectively, at the grain-filling stage. Its plant height, number of spikelets per panicle, seed setting rate and 1000-grain weight were reduced by 12.3%,9.5%, 13.0% and 5.4%, respectively, at maturation. The mutant gene was mapped to a region of 235 kb between SSR marker RM7082 and InDel marker Y2 on chromosome 2. Sequencing analysis of candidate genes between the mutant and its wild-type revealed a single-nucleotide G-to-T mutation was found at position 235 in the coding region of the LOC_Os02g09750 gene for lycopene β-cyclase, which resulted in an amino acid change from Gly at position 79 to Cys in the encoded product. The zebra524 mutant gene was allelic to β-OsLCY gene which was documented previously.