Phytic Acid and Transporters: What Can We Learn from low phytic acid Mutants?

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).

MRP Transporters and Low Phytic Acid Mutants in Major Crops: Main Pleiotropic Effects and Future Perspectives

“…( Gillman et al, 2009 ; Saghai Maroof et al, 2009 ; Gillman et al, 2013 ), Phaseolus vulgaris L. ( Panzeri et al, 2011 ; Cominelli et al, 2018 ), Triticum aestivum (RNAi lines in the ABCC13 genes), ( Bhati et al, 2016 ) ( Supplementary Material Table 1 ). Although the gene structure (exon-intron arrangement) of PA-MRP transporters is similar in the different crops ( Cominelli et al, 2020b ), the main difference between cereals (excluding the hexaploid wheat harbouring three different ABCC13 genes) and legumes is in gene number: maize and rice are characterized by a single gene copy ( ZmMRP4 and OsMRP5 , respectively), while legumes have two or three paralogues: PvMRP1 and PvMRP2 in common bean and GmMRP3 , GmMRP13 , and GmMRP19 in soybean ( Panzeri et al, 2011 ; Sparvoli and Cominelli, 2014 ; Cominelli et al, 2018 ). Indeed, these two species shared a whole-genome duplication event ( Lavin et al, 2005 ) and later soybean underwent another independent whole-genome duplication ( Schmutz et al, 2010 ).…”

“…In hexaploid wheat, three copies of the TaABCC13 gene are present and the encoded proteins show a high degree of similarity with the other cereal PA-MRP transporters ( Cominelli et al, 2020b ). The TaABCC13 proteins have been previously described as cadmium transporters ( Bhati et al, 2015 ).…”

“…A high proportion of these lpa mutants have been shown to carry mutations in genes coding for MRPs. These proteins belong to the ABCC cluster of plant ATP-binding cassette (ABC) transporters found in many species which translocate anions of various organic molecules across intra-cellular membranes ( Shi et al, 2007 ; Gillman et al, 2009 ; Nagy et al, 2009 ; Xu et al, 2009 ; Panzeri et al, 2011 ; Sparvoli and Cominelli, 2014 ; Cominelli et al, 2020b ). Such a class of mutants appears the most interesting one, since it shows the highest drop in PA level together with a concomitant substantial increase of free P and a consequent supposed increase in free cations.…”

Plant Sulfate Transporters in the Low Phytic Acid Network: Some Educated Guesses

“…Interestingly, all the mutations described thus far affect putative SULTR genes belonging to the SULTR3 subfamily, which includes elements whose functions are still objects of debate. For a detailed description of the SULTR3/lpa alleles, readers are referred to Cominelli et al [57].…”

A single nucleotide substitution in the SPDT transporter gene reduced phytic acid and increased mineral bioavailability from Rice grain ( Oryza sativa L.)

“…The reduction in PA content can be achieved through the identification of natural mutations in different kind of transporters that control P transportation in the vacuole (ABC transporter) and transporter involved in the P loading and organ/intracellular specific distribution (sulfate transporters) (Cominelli et al., 2020; Iwai et al., 2012; Kumar et al., 2021). Cominelli et al., 2020 reviewed the description of various genes, proteins and mutants related to various transporters in legumes and cereals. The attention needs to be given to the mutants which are devoid of any negative pleiotropic effects such as the mutant affected by the common bean MRP1 , rice and barley SULTR3 ; 3 and rice SULTR3 ; 4 genes.…”