Isolation and characterization of novel Phaseolus vulgaris low phytic acid mutants

Phytic acid (PA) is the major phosphorus storage sink within the plant seed. It is one of the most highly electronegative molecules present in the cell and it chelates positively charged metal ions, such as Mg2+, Fe2+, Zn2+, Mn2+ and Ca2+, important for human nutrition, reducing their bioavailability. For this reason, it is considered an antinutrient. Plant breeders have spent many efforts to isolate and develop low phytic acid (lpa) mutants in different important crops. In Phaseolus vulgaris, two allelic low phytic acid (lpa1-lpa12) mutants have been identified and characterized. These mutations are in the PvMRP1 gene coding for a putative tonoplastic phytic acid transporter. Other 29 putative mutants, showing altered PA content, have been recently identified. Three of these putative mutants have been initially characterized. Two showed reduced levels of PA and were thus considered as lpa mutants, the third one showed an increased free phosphate content, without a significant decrease in PA content, and was classified as a high inorganic phosphate (hip) mutant. These mutants, grown under standard conditions in a growth chamber, do not show any evident phenotypic alterations, compared to the BAT 93 common bean reference genotype plants. A candidate gene approach for these mutants did not reveal any mutation in known PA biosynthetic genes or in genes coding for PA transporters. A mapping approach is underway in order to identify the affected genes.