Fine mapping of QTLs for rice grain yield under drought reveals sub-QTLs conferring a response to variable drought severities

Fine-mapping studies on four QTLs, qDTY 2.1 , qDTY 2.2, qDTY 9.1 and qDTY 12.1 , for grain yield (GY) under drought were conducted using four different backcross-derived populations screened in 16 experiments from 2006 to 2010. Composite and Bayesian interval mapping analyses resolved the originally identified qDTY 2.1 region of 42.3 cM into a segment of 1.6 cM, the qDTY 2.2 region of 31.0 cM into a segment of 6.7 cM, the qDTY 9.1 region of 32.1 cM into two segments of 9.4 and 2.4 cM and the qDTY 12.1 region of 10.6 cM into two segments of 3.1 and 0.4 cM. Two of the four QTLs (qDTY 9.1 and qDTY 12.1 ) having effects under varying degrees of stress severity showed the presence of more than one region within the original QTL. The study found the presence of a donor allele at RM262 within qDTY 2.1 and RM24334 within qDTY 9.1 showing a negative effect on GY under drought, indicating the necessity of precise fine mapping of QTL regions before using them in marker-assisted selection (MAS). However, the presence of sub-QTLs together in close vicinity to each other provides a unique opportunity to breeders to introgress such regions together as a unit into high-yielding drought-susceptible varieties through MAS.针对干旱胁迫下籽粒产量（Grain Yield, GY）相关的4个数量性状基因座（Quantitative Trait Locus, QTL）——qDTY 2.1、qDTY 2.2、qDTY 9.1与qDTY 12.1，本研究利用2006至2010年间16项试验中完成筛选的4个不同回交衍生群体，开展了精细定位研究。通过复合区间作图法与贝叶斯区间作图法分析，研究团队将初定位得到的42.3厘摩（centimorgan, cM）的qDTY 2.1区域拆解为1.6 cM的片段；将31.0 cM的qDTY 2.2区域拆解为6.7 cM的片段；将32.1 cM的qDTY 9.1区域拆解为9.4 cM与2.4 cM两个片段；将10.6 cM的qDTY 12.1区域拆解为3.1 cM与0.4 cM两个片段。4个QTL中的2个（qDTY 9.1与qDTY 12.1）可在不同程度的胁迫强度下发挥调控效应，其原始定位区域内存在多个独立的调控区段。本研究发现，qDTY 2.1区域内RM262位点与qDTY 9.1区域内RM24334位点的供体等位基因会对干旱胁迫下的籽粒产量产生负面影响，这表明在将QTL区域应用于标记辅助选择（MAS）前，对其开展精准精细定位具有重要必要性。不过，多个亚QTL紧密连锁分布的特性，为育种学家通过标记辅助选择将这些区域作为一个整体单元导入高产干旱敏感品种中提供了独特的机遇。