Phytic acid phosphorus and inorganic phosphorus composition in seeds of soybean lines with independent inositol pentakisphosphate 2-kinase mutations

Abstract

Soybean [Glycine max (L.) Merr] seeds contain a large amount of phosphorus (P), which is stored as phytic acid (PA). PA is indigestible by nonruminant livestock and considered an anti-nutritional factor because PA chelates divalent cations and prevents the uptake of essential nutrients. Interest in reducing PA has increased greatly over the years and several low PA soybean lines have been discovered; however, many of these lines have inadequate germination and emergence. A gamma irradiated soybean line, ZC-2, with 50% reduction in PA was found to have excellent germination and emergence. The low PA phenotype was a result of a mutation in a gene orthologous to inositol pentakisphosphate 2-kinase (IPK1; Glyma14g07880), which is responsible for phosphorylating inositol pentakisphosphate into PA. Our own fast neutron irradiated line, FN38, has a large deletion of an independent gene homologous to IPK1 (Glyma06g03310), as well as two homeobox genes (HOX; Glyma06g03200 and Glyma06g03210). Preliminary studies have shown that HOX genes are responsible in leaf architecture. Our objectives were to characterize the deletion in FN38, determine if deleted HOX genes were the cause of the multifoliate phenotype, and reduce PA levels by more than 50% with conventional breeding methods. Jake was bred with FN38 to develop a segregating population, and we designed primers and used them to determine the presence or absence in the deletion. ZC-2 and FN38 were bred to decrease PA by more than 50%, and we developed and utilized molecular marker assays to select for the two IPK1 mutations. We performed high-performance liquid chromatography (HPLC) to measure PA levels and a colorimetric assay to measure Pi levels in the selected soybean lines. Initial characterization of PA and inorganic phosphorus (Pi) levels for the deletion indicated that a mutated Glyma06g03310 IPK1 gene does not increase Pi or decrease PA by itself. The deleted HOX genes may be responsible for the multifoliate phenotype because all progeny lines containing the del