Molecular and quantitative genetic analysis of seed size in Faba Bean (Vicia faba L.)

在谷物豆类中，种子大小是一个与产量有关的主要性状，在不同物种之间也有很大的差异，在蚕豆中发现了一个极端的例子，小群体和大群体之间的种子大小可以相差约15倍。在蚕豆中，种子大小由种皮的大小控制，种皮是母体器官。为了阐明种子大小的遗传控制，将测定两个种子大小差异较大的近等基因系在种皮生长的不同阶段的转录组图谱。这将得到两个品系杂交产生的RIL群体中种子大小的QTL定位的补充。通过分析转录组图谱，将确定两个等基因系之间种子大小差异的基础上的差异表达基因网络。为了确定造成种子大小差异的原因，转录组分析的结果将与QTL定位结果相结合。为此，转录本将首先被定位在元胞紫花苜蓿的基因组序列上，而已知的元胞紫花苜蓿和蚕豆之间的同步性将被用来识别在所定位的QTL的可信区间内的差异表达基因。根据基因本体论分析和文献中的信息，将选择一组候选基因用于所定位的QTL，并将通过qPCR验证它们的表达谱。最后，所选择的候选基因对种子大小的表型效应将在为该性状分离的三个F2群体中至少两个群体中得到验证，该群体将由与等基因系无关的小基因和大基因之间的杂交发展而来。

In grain legumes seed size, a major yield related trait, varies considerably between species but also within species, with an extreme case found in Vicia faba, where seed size between the minor and major groups can vary by a factor of about 15. In faba bean, seed size is controlled by the size of the seed coat, a maternal organ. To elucidate the genetic control of seed size, transcriptome profiles will be determined at different stages during the growth of the seed coat in two near isogenic lines of faba bean distinguished by a large difference in seed size. This will be complemented by a QTL mapping for seed size in a RIL population derived from a cross of the two lines. By analysing the transcriptome profiles, the differentially expressed gene networks, underlying the difference in seed size between the two isogenic lines, will be identified. To identify the causal factors responsible for the seed size difference, the results from the transcriptome profiling will be combined with the QTL mapping results. For this, the transcripts will first be mapped on the genome sequence of Medicago truncatula and the known synteny between M. truncatula and V. faba will be used to identify differentially expressed genes which fall within the confidence intervals of mapped QTL. Based on gene ontology analyses and information available from the literature, a set of candidate genes for the mapped QTL will be selected and their expression profiles will be verified by qPCR. Finally, the phenotypic effects of the selected candidate genes with respect to seed size will be verified in at least two of three F2 populations segregating for this trait, which will be developed from crosses between minor and major genotypes unrelated to the isogenic lines.