Phytic acid transport in Phaseolus vulgaris: a new low phytic acid mutant in the PvMRP1 gene and study of the PvMRPs promoters in two different plant systems

Phytic acid (InsP6) is the main storage form of phosphate in seeds. In the plant it plays an important role in response to environmental stress and hormonal changes. InsP6 is a strong chelator of cations, reducing the bioavailability of essential minerals in the diet. Only a common bean low phytic acid (lpa1) mutant, affected in the PvMRP1 gene, coding for a putative tonoplastic phytic acid transporter, was described so far. This mutant is devoid of negative pleiotropic effects normally characterising lpa mutants. With the aim of isolating new common bean lpa mutants, an ethyl methane sulfonate mutagenized population was screened, resulting in the identification of an additional lpa1 allele. Other putative lpa lines were also isolated. The PvMRP2 gene is probably able to complement the phenotype of mutants affected in the PvMRP1 gene in tissues other than the seed. Only the PvMRP1 gene is expressed at appreciable levels in cotyledons. Arabidopsis thaliana and Medicago truncatula transgenic plants harbouring 1.5 kb portions of the intergenic 5' sequences of both PvMRP genes, fused upstream of the GUS reporter, were generated. GUS activity in different organs suggests a refined, species-specific mechanisms of regulation of gene expression for these two PvMRP genes.