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

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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.