A rice mutant (Oryza sativa L. cv. Zhenhui249) is characterized by yellowish-green leaf, which can be easily distinguished from the wild type because no individual with mid-color between mutant and wild type was observed. The photosynthetic apparatus of the mutant was rather stable in the whole life span of the leaf, certain amount of chlorophyll b decreased in this mutant (Dai et al. 2000). In order to study the molecular mechanisms of leaf color development and photosynthesis in rice, we are attempting to isolate the gene controlling yellowishgreen leaf.

To determine the genetic mode of the mutation, the yellowish-green leaf mutant was crossed to two normal cultivars, W002 and PAI64, respectively. Two weeks after transplanting, the yellowish-green leaf mutation could be well identified. The yellowish-green leaf phenotype was not expressed in F₁ plants, while both the F₂ populations derived from the two crosses, Mutant/W002 and Mutant/PAI64, showed the same segregation ratio of three wild-type to one yellowish-green leaf phenotype (Table 1). It was revealed that the mutation was controlled by a single recessive nuclear gene, henceforth tentatively symbolized as yl(t), representing the yellow-green leaf gene.

For mapping yl(t), genomic DNAs from 195 F₂ seedings (YL(t)/YL(t), YL(t)/yl(t), and yl(t)/yl(t) ) derived from the cross of Mutant/W002 were extracted for SSR analysis (Temnykh et al. 2000, McCouch et al. 2002). Among the 512 pairs of SSR (simple sequence repeat) primers throughout all the chromosomes 70 pairs showed polymorphism between the two parents. The linkage between the yl(t) locus and SSR markers were investigated by BSA (Bulked Segregation Analysis) method with minor modification. Linkage analysis indicated that the yl(t) locus was linked with some SSR markers located on the middle of chromosome 5 and yl(t) gene was successfully mapped between the two SSR markers RM3838 and RM169 with map distances of 3.4cM and 13.9 cM, respectively (Fig. 1). Comparison of the chromosomal locations and leaf color phenotypes indicated that this gene is different from the previously identified leaf color genes (Nagato et al. 1998). Fine mapping for this gene controlling yellowish-green leaf is underway with several new markers and segregation populations on large scale.

References

Dai X., S. Cao, X. Xu, W. Lu, R. Zhang, C. Xu, Y. Chen and T. Kuang. 2000. Study on a mutant with low content chlorophyll b in a high yielding rice and its photosynthesis properties, Acta Botanica Sinica 42 (12): 1289-1294.

McCouch S., L.Teytelman, Y.Xu, K.Lobos, K.Clare, M. Walton, B. Fu, R. Maghirang, Z. Li, Y. Xing, Q. Zhang, I. Kono, M. Yano, R. Fjellstrom, G. DeClerck, D. Schneider, S. Cartinhour, D. Ware and Lincoln Stein. 2002. Development and mapping of 2240 new SSR markers for rice (Oryza sativa L.). DNA Research 9: 199-207.

Nagato, Y., A.Yoshimura and Conveners. 1998. Report of the committee on gene symbolization, nomenclature and linkage groups. Rice Genet Newslett 15: 34-74.

Temnykh S., W. Park, N. Ayres, S. Cartinhour, N. Hauck, L. Lipovich, Y. Cho, T. Ishii and S. McCouch. 2000. Mapping and genome organization of microsatellite sequences in rice (Oryza sativa L.). Theor Appl Genet 100: 697-712.