Genetic interactions regulating seed phytate and oligosaccharides in soybean (Glycine max L.)

Two low-phytate soybean (Glycine max(L.) Merr.) mutant lines- V99-5089 (mipsmutation on chromosome 11) and CX-1834 (mrp-landmrp-nmutations on chromosomes 19 and 3, respectively) have proven to be valuable resources for breeding of low-phytate, high-sucrose, and low-raffinosaccharide soybeans, traits that are highly desirable from a nutritional and environmental standpoint. A recombinant inbred population derived from the cross CX1834 x V99-5089 provides an opportunity to study the effect of different combinations of these three mutations on soybean phytate and oligosaccharides levels. Of the 173 recombinant inbred lines tested, 163 lines were homozygous for various combinations of MIPS and two MRP loci alleles. These individuals were grouped into eight genotypic classes based on the combination of SNP alleles at the three mutant loci. The two genotypic classes that were homozygousmrp-l/mrp-nand either homozygous wild-type or mutant at themipslocus (MIPS/mrp-l/mrp-normips/mrp-l/mrp-n) displayed relatively similar similar to 55% reductions in seed phytate, 6.94 mg g(-1)and 6.70 mg g(-1)respectively, as compared with 15.2 mg g(-1)in the wild-type MIPS/MRP-L/MRP-N seed. Therefore, in the presence of the double mutantmrp-l/mrp-n, themipsmutation did not cause a substantially greater decrease in seed phytate level. However, the nutritionally-desirable high-sucrose/low-stachyose/low-raffinose seed phenotype originally observed in soybeans homozygous for themipsallele was reversed in the presence ofmrp-l/mrp-nmutations: homozygousmips/mrp-l/mrp-nseed displayed low-sucrose (7.70%), high-stachyose (4.18%), and the highest observed raffinose (0.94%) contents per gram of dry seed. Perhaps the block in phytic acid transport from its cytoplasmic synthesis site to its storage site, conditioned bymrp-l/mrp-n, alters myo-inositol flux inmipsseeds in a way that restores to wild-type levels themipsconditioned reductions in raffinosaccharides. Overall this study determined the combinatorial effects of three low phytic acid causing mutations on regulation of seed phytate and oligosaccharides in soybean.