MRP transporters and low phytic acid mutants in major crops: main pleiotropic effects and future perspectives

Phytic acid (PA) represents the major storage form of seed phosphate (P). During seed maturation, it accumulates as phytate salts chelating various mineral cations, thereforereducing their bioavailability. During germination, phytase dephosphorylates PA releasingboth P and cations which in turn can be used for the nutrition of the growing seedling.Animals do not possess phytase, thus monogastric animals assimilate only 10% of thephytate ingested with feed, whilst 90% is excreted and may contribute to cause Ppollution of the environment. To overcome this double problem, nutritional andenvironmental, in the last four decades, many low phytic acid (lpa) mutants (most ofwhich affect the PA-MRP transporters) have been isolated and characterized in all majorcrops, showing that the lpa trait can increase the nutritional quality of foods and feeds andimprove P management in agriculture. Nevertheless, these mutations are frequentlyaccompanied by negative pleiotropic effects leading to agronomic defects which mayaffect either seed viability and germination or plant development or in some cases evenincrease the resistance to cooking, thus limiting the interest of breeders. Therefore,although some significant results have been reached, the isolation of lpa mutantsimproved for their nutritional quality and with a good field performance remains a goalso far not fully achieved for many crops. Here, we will summarize the main pleiotropiceffects that have been reported to date in lpa mutants affected in PA-MRP transporters infive productive agronomic species, as well as addressing some of the possible challengesto overcome these hurdles and improve the breeding efforts for lpa mutants.