Two independent grain-length mutants mapped to a single region on the long arm of chromosome 2 in rice

ABSTRACT Grain shape in rice is a key determinant of grain appearance, yield and market value, and thus has been widely studied. Rice mutant lines with long-grain phenotypes were previously isolated from an M2 population derived from mutagenized mature pollen grains that were treated with gamma-ray irradiation for a cultivar Ma85. To understand the genetic basis underlying the long-grain trait, two mutant lines, JF171 and JF178, were crossed with the short-grain parents JF222 and Samba, generating three F2 populations. Molecular marker-based genetic analysis was employed to detect the major QTLs that affected grain length, grain width, length-to-width ratio and grain weight. Based on the data obtained for the three populations, a joint major QTL for grain length was mapped to a 4.7 Mb region between the SSR makers RM263 and RM318 on the long arm of chromosome 2. The results suggested that the two independent mutations contained in JF171 and JF178 are likely due to alterations in the same genetic region. Furthermore, we developed a BC2F2 population using JF178 and Samba and narrowed the region to 0.6 Mb. The results of the current study will be helpful to reveal the genetic basis of the above long-grain mutant lines. In general, our results provide solid genetic data to identify the unknown gene that affects grain length by map-based cloning and practice marker-assisted breeding for long-grain rice cultivars.

摘要 水稻籽粒形状是决定籽粒外观、产量与市场价值的关键性状，因此受到广泛研究。此前，本研究团队从以γ射线辐照诱变处理品种马85（Ma85）的成熟花粉粒所构建的M2代群体中，分离得到了具有长粒表型的水稻突变体株系。为解析该长粒性状的遗传基础，本研究选取两个突变体株系JF171与JF178，分别与短粒亲本JF222、Samba杂交，构建得到3个F2代群体。采用基于分子标记的遗传分析方法，对影响籽粒长度、籽粒宽度、长宽比及籽粒重量的主效数量性状基因座（Quantitative Trait Locus, QTL）进行检测。基于3个群体的分析数据，本研究将调控籽粒长度的联合主效QTL定位至第2号染色体长臂上简单序列重复（Simple Sequence Repeat, SSR）标记RM263与RM318之间的4.7 Mb区间内。研究结果表明，JF171与JF178所携带的两处独立突变，大概率源自同一遗传区域的序列变异。此外，本研究以JF178与Samba为材料构建了BC2F2群体，将该候选区间进一步缩小至0.6 Mb。本研究结果可为解析上述长粒突变体的遗传基础提供重要依据。总体而言，本研究所得的可靠遗传数据，可为通过图位克隆技术分离调控籽粒长度的未知基因，以及开展长粒水稻品种的标记辅助育种实践提供坚实支撑。