Molecular Mapping Of A Yellow-Green Leaf Gene Ygl2(t) In Rice (Oryza Sativa L.) And Its Application In Breeding

Crop biomass and economic yield mainly depend on the photosynthetic assimilate ofleaves and other photosynthetic organs. 90-95% dry matter accumulation in rice is resultedfrom photosynthetic assimilate of leaves, the main photosynthetic organ. Therefore it isvery important in the theoretical research of photosynthesis regulatory mechanism to mapand clone new rice photosynthetic-related genes and investigate their function. Through thegene engineering approach, the photosynthesis ability and economic efficiency of rice maybe significantly increased. As an obvious trait mutation, leaf color mutation could not onlyused in the research of photosynthesis, chlorophyll biosynthesis, structure, function,inheritance, differentiation and growth of chloroplast, but also in the identification of seedpurity for hybrid rice.Rice cultivar Wuyunjing 7, Jiangxi 1587 (upland rice) and a yellow-green leaf mutantygl2, origined from a Wuyunjing 7, was used in this study.Two reciprocals (Wuyunjing 7×ygl2, Jiangxi1587×ygl2) were made to obtain F₁ andF₂ populations. The observation of leaf color showed that all the F₁ plants were normalgreen, but the leaf color trait in the all F₂ populations was segregated into yellow green andnormal green with a segregation ratio of 3: 1. It indicated that the leaf color of mutant ygl2was controlled by a single recessive nuclear gene.The plants of F2 population, generated from the cross ygl2×Jiangxi 1587, were usedfor molecular mapping of this recessive gene. The preliminary results showed that themutant gene was located on the rice chromosome 6 between two SSR markers, RM541 andRM30, with the genetic distances of 13.13cM and 9.09cM respectively. Since there is nosimilar gene locus reported on this region, it indicates that this is new gene identified andtentatively named as ygl2(t) (yellow-green leaf 2). In order to establish the fine location ofthe ygl2(t) gene, the public rice genome sequence in the region containing ygl2(t) gene wasused to search new SSR markers. Then eight new SSR markers between RM541 and RM30 were developed. 429 yellow-green leaf plants of F₂ population generated from the crossygl2×Jiangxi 1587 were analyzed with above eight SSR markers, and the gene ygl2(t) wasmapped between SSR6-16 and RM7434 markers, with genetic distances of 0.62cM and0.74cM respectively.A new photo-thermo sensitive genic male sterile line 3290S with the yellow-green leaftag was developed in BC₁F₇ from the yellow-green leaf mutant and the photo-thermosensitive male sterile line 103S via cross, backcross and fertility identification. Goodhybrids were developed by identifying crosses from 3290S and 103S with a series of greenleaf restorer lines, and there were no obvious differences in all the main economiccharacteristics investigated, indicating that the yellow-green leaf trait had no significantnegative effect on the main economic characteristics. Meanwhile the seedlings withyellow-green leaves could be easily distinguished from the normal seedlings. Thus, it wasreasonable to breed japonica sterile lines with the yellow-green leaf tag.