Mapping the low palmitate fap1 mutation and validation of its effects in soybean oil and agronomic traits in three soybean populations.

KEY MESSAGE: fap 1 mutation is caused by a G174A change in GmKASIIIA that disrupts a donor splice site recognition and creates a GATCTG motif that enhanced its expression. Soybean oil with reduced palmitic acid content is desirable to reduce the health risks associated with consumption of this fatty acid. The objectives of this study were: to identify the genomic location of the reduced palmitate fap1 mutation, determine its molecular basis, estimate the amount of phenotypic variation in fatty acid composition explained by this locus, determine if there are epistatic interactions between the fap1 and fap nc loci and, determine if the fap1 mutation has pleiotropic effects on seed yield, oil and protein content in three soybean populations. This study detected two major QTL for 16:0 content located in chromosome 5 (GmFATB1a, fap nc) and chromosome 9 near BARCSOYSSR_09_1707 that explained, with their interaction, 66-94 % of the variation in 16:0 content in the three populations. Sequencing results of a putative candidate gene, GmKASIIIA, revealed a single unique polymorphism in the germplasm line C1726, which was predicted to disrupt the donor splice site recognition between exon one and intron one and produce a truncated KASIIIA protein. This G to A change also created the GATCTG motif that enhanced gene expression of the mutated GmKASIIIA gene. Lines homozygous for the GmKASIIIA mutation (fap1) had a significant reduction in 16:0, 18:0, and oil content; and an increase in unsaturated fatty acids content. There were significant epistatic interactions between GmKASIIIA (fap1) and fap nc for 16:0 and oil contents, and seed yield in two populations. In conclusion, the fap1 phenotype is caused by a single unique SNP in the GmKASIIIA gene.