Phytic Acid and Inorganic Phosphate Composition in Soybean Lines with Independent IPK1 Mutations

Soybean seeds contain a large amount of P, which is stored as phytic acid (PA). Phytic acid is indigestible by nonruminant livestock and considered an antinutritional factor in soybean meal. Several low PA soybean lines have been discovered, but many of these lines have either minor reductions in PA or inadequate germination and emergence. The reduced PA phenotype of soybean line Gm-lpa-ZC-2 was previously shown to be the result of a mutation in a gene encoding an inositol pentakisphosphate 2-kinase on chromosome 14 (14IPK1). While the 14IPK1 mutation was shown to have no impact on germination and emergence, the reduction in PA was modest (up to 50%). Our objective was to determine the effect on seed P partitioning for a novel mutation of an independent IPK1 gene on chromosome six (06IPK1) on its own and in combination with mutant alleles of the 14IPK1. We developed soybean populations and conducted genotype and phenotype association analyses based on the genotype of the 06IPK1 and 14IPK1 genes and the seed P partitioning profile. The lines with both mutant IPK1 genes had very low PA levels, moderate accumulation of inorganic phosphate (Pi), and accumulation of high amounts of P in lower inositols. The developed lines did not have significant reductions in germination or field emergence. In addition, characterization of the lower inositols produced in the mutant lines suggests that IPK1 is a polyphosphate kinase and provides some insight into the PA biosynthesis pathway in soybean seeds.