Fine genetic mapping of the genomic region controlling leaflet shape and number of seeds per pod in the soybean

Narrow leaflet cultivars tend to have more seeds per pod than broad leaflet cultivars in soybean Glycine max (L.) Merr.], which suggests that the leaflet-shape trait locus is tightly linked to or cosegregates with the trait locus controlling the number of seeds per pod (NSPP). Here, we attempted to further elucidate the relationship between leaflet shape and NSPP. A BC₃F₂ population from a cross between the ‘Sowon’ (narrow leaflets and high NSPP) and ‘V94-5152’ (broad leaflets and low NSPP) variants was used. The results of the molecular genetic analyses indicated that, although the NSPP characteristic, in particular, the occurrence of 4-seeded pods, is governed by additional modifying genes that are likely present in Sowon, the two traits cosegregate in the BC₃F₂ population. The mapping results generated using public markers demonstrated that the narrow leaflet-determining gene in Sowon is an allele of the previously highly studied ln gene on chromosome 20. A high-resolution map delimited the genomic region controlling both the leaflet shape and NSPP traits to a sequence length of 66 kb, corresponding to 0.7 cM. Among the three genes annotated in this 66 kb region, Glyma20g25000.1 appeared to be a good candidate for the Ln-encoding gene, owing to its 47.8% homology with the protein encoding for the JAGGED gene that regulates lateral organ development in Arabidopsis. Taken together, our results suggested that phenotypic variations for narrow leaflet and NSPP are predominantly from the pleiotropic effects of the ln gene. Thus, our results should provide a molecular framework for soybean breeding programs with the objective of improving soybean yield.