小麦粒重主效QTL QGw.nau-5A的精细定位与遗传效应研究

Grain weight, one of the three wheat yield components, plays a key role in the formation of yield. Although a number of QTLs controlling wheat grain weight have been identified, the fine mapping and map-based cloning of these QTLs has progressed slowly, limiting our understanding of the mechanism of wheat yield formation and the efficiency of high yield breeding. We mapped the QTL QGw.nau-5A, which controls grain weight on chromosome 5A in the wheat key parent Nanda2419. The QTL increases the grain weight, also increases the grain thickness and grain width, but cause a significant decrease in grain length. Localization analysis showed that the QTL interval was located in a recombination cold spot near the centromere, and it was difficult to precisely localize it by the traditional localization strategy. This project aims to screen genetic recombination using large-scale secondary F2 population with different backgrounds, and adopt approaches such as radiation hybrid mapping and natural population haplotype analysis to approach the QTL, and obtain candidates through target interval sequence assembly and bioinformatics methods. In addition, the genetic effects of the near-isogenic lines of QGw.nau-5A with different backgrounds will be evaluated in this study to identify excellent allelic variation.

粒重是小麦产量三因素之一，对产量形成起着十分关键的作用。虽然目前已定位了多个控制小麦粒重的QTL，但这些QTL的精细定位和图位克隆进展缓慢，限制了我们对小麦产量形成机制的认识和高产育种的效率。我们在小麦骨干亲本南大2419的5A染色体上定位了控制粒重的主效QTL QGw.nau-5A。该QTL不仅能增加粒重，还能增加粒厚和粒宽，但引起粒长显著降低。定位分析表明该QTL区间位于着丝粒附近的一个重组冷点区，难于通过传统的定位策略对其精细定位。本项目拟在利用不同背景的次级F2大群体筛选遗传重组的同时，采用放射杂交定位、自然群体单倍型分析等方法，迫近该QTL，并通过区间序列装配和生物信息学方法，获得候选基因，为该QTL的克隆奠定基础；此外，本研究还将通过不同背景QGw.nau-5A的近等基因系进行遗传效应评价，鉴定优异的等位变异。

粒重是小麦单产组成的关键因素之一，发掘控制粒重的关键基因资源，阐明粒重形成的遗传调控机制，实现对粒重的优化调控，对于小麦高产育种至关重要。QGw.nau-5A是申请人所在团队利用南大2419/望水白构建的重组自交系群体，从小麦5A染色体上发掘的控制粒重的主效QTL。该QTL是一个不同于已知粒重基因的未知位点，对该QTL的研究可以丰富我们对粒重调控机制的认识，为小麦高产育种提供关键基因资源。为了精细定位克隆该基因，本项目在原有基础上，利用多个背景的NIL构建的次级F2群体，并扩大次级F2群体规模，获得新的重组体类型。同时利用参考基因组序列信息设计QTL区间内分子标记，结合重组体基因型和表型，构建QGw.nau-5A所在染色体区间的饱和遗传图谱，最终将QGw.nau-5A精细定位在Xwgrb1356-Xwgrb1619区间内，定位区间的遗传距离缩小至为0.11cM，对应中国春参考基因组序列33Mb的物理距离。根据IWGSC RefSeq v1.0和比较转录组分析高粒重重材料和低粒重材料间的差异表达基因及其功能富集特征，最终确定8个可能的候选基因。结合分子标记辅助选择和高代回交策略构建了7个背景的QGw.nau-5A近等基因系，并在5个环境中验证了来自南大2419的单倍型具有增加粒重的效应。通过关联分析，在地方品种和育成品种中发掘了所在区间的12种单倍型，其中代表高粒重的南大2419单倍型（Hap1）和代表低粒重的望水白单倍型（Hap2）为优势单倍型，占83.40%。在地方品种中，Hap2为优势单倍型，在国内和国外的育成小麦品种中，Hap1为优势单倍型，分别达到91.40%和94.40%，表明该位点在育种过程中收到强烈的人工选择，进一步说明该位点可能在粒重和产量提高过程中有增效作用。