Genetic analysis and molecular mapping of a pale flower allele at the W4 locus in soybean

In soybean (Glycine max (L.) Merr.), the w4-mutable line that harbors the w4-m allele was identified in 1983. It was proposed that this line contained an autonomous transposable element at the W4 locus, which is a major locus controlling the biosynthesis of anthocyanin. The w4-m allele can revert to the W4 allele that produces the wildtype phenotype, or sometimes to other alleles that produce intermediate phenotypes. Mutant plants that produce pale flowers were identified among the progeny of a single germinal revertant event from the w4-mutable line. Through genetic analysis, we established that the pale-flower mutation was conditioned by a new allele (w4-p) at the W4 locus. The w4-p allele is dominant to the w4 allele but recessive to the W4 allele, and the w1 allele has an epistatic effect on the w4-p allele. The pale-mutant line (w4-pw4-p) was designated as Genetic Type Collection number T369. An F-2 mapping population derived from the cross of Minsoy (W4W4) x T369 (w4-pw4-p) was used to map the W4/w4-p locus, using simple sequence repeat (SSR) markers. The W4 locus was located at one end of molecular linkage group D2, 2.3 cM from the SSR marker Satt386 and close to the nearby telomere.