小麦籽粒发育QTL的精细定位与优异等位变异发掘

Grain size is an important determinant of grain yield and quality in wheat. Although many QTLs for grain weight were identified to date, few has been cloned yet. In a previous study, we mapped a major QTL QGd.nau-1B to a physical interval of 1.28 Mb on chromosome 1B, through linkage and association analyses in the Nanda2419 × Wangshuibai recombinant inbred line population and in a wheat variety population, respectively. This QTL was detected in multiple trials, and showed positive effects on grain weight, width, thickness and volume, but no negative effect on grains per spike, so called grain development QTL. It was found that QGd.nau-1B has been under strong selection in breeding, indicating its value in wheat improvement. Here, we propose to fine map this QTL using the near isogenic line-derived F2 populations, and identify the candidate gene(s) based on analyses of gene sequence variations and expression. In addition, the allelic variations of QGd.nau-1B in wheat varieties will be screened and evaluated accurately for their effects on grain development by transferring them into multiple genetic backgrounds. Favorable allelic variation will then be determined. This study would accelerate the map-based cloning of QGd.nau-1B, and exploit the favorable allelic variations for wheat breeding.

籽粒大小是小麦产量和品质的重要决定因子。目前虽有大量粒重QTL被定位，但有关QTL的克隆至今鲜有报道。申请人前期利用南大2419×望水白重组自交系和小麦品种群体，通过连锁和关联分析在多环境中鉴定到一个主效QTL QGd.nau-1B，定位于1B染色体1.28 Mb的物理区间；该QTL对粒重、粒宽、粒厚和籽粒体积都有正效应，但不负调控穗粒数，这里将其称为籽粒发育QTL。在育种中QGd.nau-1B受到强烈选择，具有重要的应用价值。本项目拟在此基础上，一方面利用近等基因系次级F2群体精细定位QGd.nau-1B，通过基因序列和表达分析，明确该QTL的候选基因；另一方面，鉴定QGd.nau-1B区段在小麦品种群体中的等位变异，采用回交转育将不同等位变异导入多个遗传背景，准确评价各变异的效应，发掘该QTL的优异等位变异类型。本研究将为QGd.nau-1B的图位克隆和优异基因资源的开发利用奠定基础。

籽粒大小既决定小麦的产量潜力，又同时影响小麦的加工品质和分级定价。因此，小麦籽粒大小的遗传改良对于提高小麦产量和品质具有重要的意义。本项目从小麦骨干亲本“南大2419”中定位到一个控制籽粒大小的主效QTL QGd.nau-1B。进一步研究发现，QGd.nau-1B包含两个亚位点：QGd.nau-1B.1和QGd.nau-1B.2。通过关联和单倍型分析，将QGd.nau-1B.1定位至767 kb区间内。该区间包括一个淀粉合成相关的基因TaAgp2，其编码葡萄糖焦磷酸化酶大亚基。利用两个重组自交系群体和小麦品种群体，进一步验证了TaAgp2即为QGd.nau-1B.1的候选基因。对于QGd.nau-1B.2，利用剩余杂合子和近等基因系验证了其能产生更大、更圆的籽粒。在该区间开发了13个新的分子标记，构建了高密度遗传图谱。利用近等基因系次级F2群体筛选获得了153个重组体。结合重组体的基因型和表型，将QGd.nau-1B.2精细定位至1.8 Mb。该区间包括5种单倍型，不同单倍型近等基因系分析发现，南大2419、扬麦17、早洋麦、中优9507等小麦品种携带大粒、高产的等位变异。通过回交和分子标记辅助选择，已将优异等位变异转入不同生态区的推广品种中，获得了育种可用的中间材料。本研究结果不仅有助于解析小麦籽粒大小形成的分子遗传机制，也为小麦高产优质育种提供了基因资源。