Functional characterization of PvMRP1 and PvMRP2, two putative phytic acid transporters.

Phytic acid is the main storage form for phosphate in plant seeds. It decreases the nutritional value of the seeds by trapping phosphate and chelating nutritionally important minerals, such as iron, zinc, magnesium, and calcium. Therefore, the isolation of low phytic acid (lpa) mutants is considered a highly desirable objective in the genetic improvement of the nutritional quality of grain crops. The lpa1(280-10) mutant isolated in Phaseolus vulgaris confers a 90% reduction in seed phytic acid content, a 25% reduction in raffinosaccharide content, sevenfold increase of free iron cations in the seeds and does not display pleiotropic effects and agronomic defects. The mutated gene corresponds to PvMRP1, coding for an ATP-Binding Cassette transporter. The Arabidopsis AtMRP5 homolog of PvMRP1 has been characterized by reverse genetics approach: the atmrp5-1 insertion mutant displays lpa seeds, modified root architecture, reduced sensitivity to abscisic acid in seed germination and in guard cells, improved drought tolerance and water use efficiency. Recently it was reported the first direct evidence that AtMRP5 is a vacuolar phytic acid transporter. In Phaseolus there is also PvMRP2, paralog of PvMRP1, while in Arabidopsis there is only one gene. PvMRP2 is probably able to complement the lpa1 (280-10) phenotype in other tissues than the seed, thus explaining the lack of pleiotropic effects in the bean mutant. The aim of this work is the functional characterization of PvMRP1 and PvMRP2 through expression analysis, subcellular localization and complementation of the Arabidopsis atmrp5 mutant. Here we show preliminary data and our working model.