Abstract
Phytic acid has two main roles in plant tissues: Storage of phosphorus and regulation of different cellular processes. From a nutritional point of view, it is considered an antinutritional compound because, being a cation chelator, its presence reduces mineral bioavailability from the diet. In recent decades, the development of low phytic acid (lpa) mutants has been an important goal for nutritional seed quality improvement, mainly in cereals and legumes. Different lpa mutations affect phytic acid biosynthetic genes. However, other lpa mutations isolated so far, affect genes coding for three classes of transporters: A specific group of ABCC type vacuolar transporters, putative sulfate transporters, and phosphate transporters. In the present review, we summarize advances in the characterization of these transporters in cereals and legumes. Particularly, we describe genes, proteins, and mutants for these different transporters, and we report data of in silico analysis aimed at identifying the putative orthologs in some other cereal and legume species. Finally, we comment on the advantage of using such types of mutants for crop biofortification and on their possible utility to unravel links between phosphorus and sulfur metabolism (phosphate and sulfate homeostasis crosstalk).
Highlights
Phytic acid (PA), chemically myo-inositol-1,2,3,4,5,5-hexakisphosphate, is the major form of phosphorus (P) storage in seeds and in other plant organs, such as pollen, roots, tubers, and turions
PA is synthesized in the cytosol through two different routes: (i) The lipid-independent pathway, the most used in the seed, consisting of the sequential phosphorylation of the 6-carbon myo-inositol and soluble inositol phosphates (InsPs), and (ii) the lipid-dependent pathway, using precursors that include phosphatidylinositol (PtdIns) and PtdIns phosphates
Fact, very recently, Ding localization. These data are in agreement with those reported on and co-workers [89] demonstrated that AtSULTR3;4/SULTR-like Phosphorus Distribution Transporter (SPDT) functions as a high-affinity Pibelow transporter, mutations affecting the HvST, OsSULTR3;3 and OsSULTR3;4 genes which confer grain lpa phenotype being able to mediate Pi uptake when injected in the Xenopus oocyte
Summary
Phytic acid (PA), chemically myo-inositol-1,2,3,4,5,5-hexakisphosphate, is the major form of phosphorus (P) storage in seeds (up to 85% of total P) and in other plant organs, such as pollen, roots, tubers, and turions. The mutations belonging to the (i) and (iii) classes induce a decrease of PA amount, accompanied by a molar equivalent increase of inorganic phosphate (Pi ) in the homozygous mutants. They are usually perturbed in different branches of the biosynthetic pathway common to PA and other compounds (e.g., galactinol, raffinose, stachyose, and ascorbic acid). Particular emphasis will be given to the reported differences among cereals and legumes of lpa mutant phenotypes in the PA-MRP genes, depending on the presence of one or more partially redundant copies of these genes and to their tissue-specific expression. We will highlight how the study of these mutants may help to elucidate phosphate and sulfur metabolism, and the possible roles that the transporters described here may play
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