Mapping QTLs for Grain Weight and Shape Using Four Sister Near Isogenic Lines of Rice

For mapping quantitative trait loci (QTLs) for grain weight (GW) and grain shape in rice (Oryza sativa L.), a small GW variety, Nipponbare, was crossed with the largest GW line, SLG-1 to construct the mapping populations. In the cross progenies, large GW plants were selected to backcross with Nipponbare for several rounds. In the BC4F1 population, which contained 73 lines, the distribution of GW appeared in 4 peaks. A single plant at each peak was selected to develop a SNIL population. Based on bulked segregant analysis, 19 polymorphic markers associated with GW and grain shape were screened from the 1513 simple sequence repeat (SSR) markers covering the 12 chromosomes of rice. Using the 19 SSR markers, QTLs for GW, grain length, seed width, and grain thickness were identified in the 4 SNIL populations independently. A total of 12 QTLs were located in 6 regions on chromosomes 2, 3, 6, and 8, including genes GS3 and GW2 that have been cloned already. These QTLs explained phenotypic variations ranging from 7.22% to 53.38%. Five QTLs between RM6318 and RM1367 on chromosome 2, between RM5477 and RM6417 on chromosome 3, and between RM3370 and RM1161 on chromosome 6 were potential and required fine mapping. Among them, qGL3-1 is a novel locus with contribution on GL as high as 11.41-21.27%. These results and the SNILs constructed provide a basis for the fine mapping and gene cloning of novel locus associated with GW and grain shape in rice.

摘 要粒重是决定水稻产量的三要素之一。利用世界上粒重最大的品种之一SLG-1(供体亲本)与小粒品种日本晴(Nipponbare, 轮回亲本)杂交, 在各回交世代选择粒重较大单株与日本晴回交, 构建水稻粒重和粒形的姊妹近等基因系(SNILs)。对获得的73株BC4F1单株进行粒重频率分布统计, 选择粒重频率分布在4个峰值处的代表性单株, 自交获得4个BC4F2SNILs群体。利用BSA法(分离群体分组混合分析法), 从均匀分布在水稻染色体上的1 513对SSR标记中筛选出与粒重和粒形相关的多态性标记19对, 以LOD≥2.5作为选择阈值, 对粒重、粒长、粒宽和粒厚进行QTL扫描, 共检测到6个区域的12个QTL, 贡献率从7.22%到53.38%。这些QTL所在区域包含已克隆的粒长GS3和粒宽GW2, 也包含没有精细定位的第2染色体的RM6318∼RM1367、第3染色体的RM5477∼RM6417和第6染色体的RM3370∼RM1161等3个区域控制粒重和粒形的5个QTL。其中第3染色体上RM5477∼RM6417区间存在粒形贡献率较大的新的QTL。构建含有这些粒重QTL的姊妹近等基因系, 为进一步精细定位或克隆新的粒重或粒形QTL奠定了基础。