Biochemical and Molecular Characterization of a Mutation That Confers a Decreased Raffinosaccharide and Phytic Acid Phenotype on Soybean Seeds

Abstract

A single, recessive mutation in soybean (Glycine max L. Merr.), which confers a seed phenotype of increased inorganic phosphate, decreased phytic acid, and a decrease in total raffinosaccharides, has been previously disclosed (S.A. Sebastian, P.S. Kerr, R.W. Pearlstein, W.D. Hitz [2000] Soy in Animal Nutrition, pp 56-74). The genetic lesion causing the multiple changes in seed phenotype is a single base change in the third base of the codon for what is amino acid residue 396 of the mature peptide encoding a seed-expressed myo-inositol 1-phospate synthase gene. The base change causes residue 396 to change from lysine to asparagine. That amino acid change decreases the specific activity of the seed-expressed myo-inositol 1-phosphate synthase by about 90%. Radio tracer experiments indicate that the supply of myo-inositol to the reaction, which converts UDP-galactose and myo-inositol to galactinol is a controlling factor in the conversion of total carbohydrate into the raffinosaccharides in both wild-type and mutant lines. That same decrease in myo-inositol 1-phosphate synthetic capacity leads to a decreased capacity for the synthesis of myo-inositol hexaphosphate (phytic acid) and a concomitant increase in inorganic phosphate.

The genetics of phytate and phosphate accumulation in seeds and leaves of Arabidopsis thaliana, using natural variation

“…Hitz et al (2002) reported about the biochemical and molecular characterisation of a mutation that confers a decreased raffinose oligosaccharide and InsP6 phenotype on soybean seeds. This can be explained by the fact that InsP6 and raffinose oligosaccharides share at least myoinositol-1-phosphate and possibly free myo-inositol as a common intermediate (Loewes and Murthy 2000).…”

“…However, relatively little is known about plant genomic sequences encoding functions in the late part of the pathway, playing a direct role in seed InsP6 accumulation and mobilisation (Raboy 2001). Only recently, Hitz et al (2002) reported that a defective myoinositol-1-phosphate synthase decreased the amount of InsP6 in soybean seeds. Furthermore, it is known that during germination InsP6 is broken down by phytase enzymes, releasing myo-inositol and mineral contents.…”

RNAi-mediated silencing of the myo-inositol-1-phosphate synthase gene (GmMIPS1) in transgenic soybean inhibited seed development and reduced phytate content

“…Inositol can be converted into phytic acid (phytate), the most abundant form of phosphate in seeds, accounting for 50-90% of total seed phosphorus in several species (Loewus and Murthy 2000;Raboy 2001Raboy , 2002Raboy et al 2001). The path to phytate has been suggested to proceed via the sequential phosphorylation of inositol phosphates, and/or in part via phosphatidylinositol phosphate (Brearley and Hanke 1996a, b;Loewus and Murthy 2000;Raboy 2001Raboy , 2002Hitz et al 2002). Phytate is presumed to act as a phosphate storage compound (Brearley and Hanke 1996a, b).…”

Variability in the oligosaccharide concentration in seeds of the mapping population of pea (Pisum sativum L.)

“…Jones et al (1999) screened 70 pea lines from the John Innes Pisum germplasm collection (Norwich, UK) and selected lines which had unusual RFO composition: traces of raffinose or verbascose and a broad range of stachyose concentration. In soybean unique lines containing low raffinose or low stachyose were also found (Hitz et al 2002). The QTL analysis in soybean located four QTL for oligosaccharide content.…”

“…In the soybean genome appears one (out of two identified) raffinose synthase gene, completely associated with the low raffinose and low stachyose phenotype (Dierking & Bilyeu 2008). A single mutation in a soybean seed expressing the myo-inositol 1-phosphate synthase gene leads to a dramatic reduction of enzyme activity and decreases the accumulation of RFOs (Hitz et al 2002). The reduction of RFO level can be achieved also by genetic manipulation.…”