Origin and Seed Phenotype of Maize low phytic acid 1-1 and low phytic acid 2-1  

Abstract

Phytic acid (myo-inositol-1, 2, 3, 4, 5, 6-hexakisphosphate or Ins P 6 ) typically represents approximately 75% to 80% of maize (Zea mays) seed total P. Here we describe the origin, inheritance, and seed phenotype of two non-lethal maize low phytic acid mutants, lpa1-1 and lpa2-1. The loci map to two sites on chromosome 1S. Seed phytic acid P is reduced in these mutants by 50% to 66% but seed total P is unaltered. The decrease in phytic acid P in mature lpa1-1 seeds is accompanied by a corresponding increase in inorganic phosphate (P i ). In mature lpa2-1 seed it is accompanied by increases in P i and at least three other myo-inositol (Ins) phosphates (and/or their respective enantiomers): d-Ins(1,2,4,5,6) P 5 ; d-Ins (1,4,5,6) P 4 ; and d-Ins(1,2,6) P 3 . In both cases the sum of seed P i and Ins phosphates (including phytic acid) is constant and similar to that observed in normal seeds. In both mutants P chemistry appears to be perturbed throughout seed development. Homozygosity for either mutant results in a seed dry weight loss, ranging from 4% to 23%. These results indicate that phytic acid metabolism during seed development is not solely responsible for P homeostasis and indicate that the phytic acid concentration typical of a normal maize seed is not essential to seed function.

A paramutation phenomenon is involved in the genetics of maize low phytic acid1-241 (lpa1-241) trait

“…They produce seeds with reduced phytic acid content and a proportionally higher level of free phosphate, whereas the total amount of seed P is not significantly altered (Raboy et al, 2000, Pilu et al, 2003Shi et al, 2005). The high inorganic phosphate phenotype (HIP) associated with the lpa1 phenotype can be quickly determined using Chen's assay (Chen et al, 1956), so lpa mutant seeds can easily be screened.…”

“…The high inorganic phosphate phenotype (HIP) associated with the lpa1 phenotype can be quickly determined using Chen's assay (Chen et al, 1956), so lpa mutant seeds can easily be screened. Regarding lpa1 mutants, there is evidence indicating that they map on the short arm of chromosome 1, where a mips1s sequence has been localized too (Raboy et al, 2000).…”

“…Although biochemical, mapping and gene expression data suggest the mips1s gene as a candidate for lpa1 mutation in maize (Raboy et al, 2000;Pilu et al, 2003;Shukla et al, 2004;Pilu et al, 2005), recent transposon mutagenesis experiments found that a novel gene designated ZmMRP4 (accession number EF86878), coding a multidrug resistance-associated-protein (MRP) mapping near the mips1s sequence, is the actual responsible gene for lpa1 mutation (Shi et al, 2007). MRP proteins represent a subfamily of ATP-binding cassette transmembrane transporters widespread in all eukaryotes, which in plants are involved in several functions, such as xenobiotic detoxification, organic ions transport, oxidative stress tolerance (Swarbreck et al, 2003) and even transpiration control (Klein et al, 2006).…”

Phosphorus Compounds in Sequential Extracts of Animal Manures: Chemical Speciation and a Novel Fractionation Procedure

“…To address this, strategies involving dietary manipulation are being adopted to reduce manure phosphorus concentrations. For monogastric animals, which cannot digest phytic acid, such strategies include the isolation of mutant grains with low phytic acid concentrations (5) and supplementation of diets with microbial phytase to hydrolyze phytic acid in the gut (6). Such dietary manipulations alter the phosphorus composition of manure and influence its fate in the environment.…”

Dietary low-phytate mutant-M 955 barley grain alters phytate degradation and mineral digestion in sheep fed high-grain diets

“…Awareness of P excretion into the environment (Sharpley et al, 1994) has brought about an intensive search for, and subsequent identification of, mutant low-phytate cereal grains (e.g., Raboy et al, 2000). These mutant grains contain similar amounts of total P as the non-mutant varieties, but have substantially less P existing as phytate.…”