Tolerance to Phosphorus Deficiency Improves Seed Phytic Acid-to-Iron Molar Ratios in Common Bean

Although significant advances have been achieved in the biofortification of common beans to overcome deficiencies in Zinc (Zn) and iron (Fe), the mechanisms involved remain poorly understood. We thus explored the relationships between phosphorus nutrition and Zn and Fe accumulation in four bean genotypes (Edar, Nizok, Colorado and Chimbolos) that nominally show differences in seed Fe and Zn accumulation. In contrast to other genotypes, while phosphorus availability had no effect on seed Fe accumulation, phosphorus and phytate levels were decreased in all lines under phosphorus deficiency. Edar plants had a higher seed yield under low phosphorus conditions than the other lines. Analysis of the seed proteome also revealed that Edar is highly resistant to phosphorus deficiency, with similar seed Fe accumulation but lower phytate levels. The phytic acid-to-Fe molar ratios in Edar seeds produced under low phosphorus nutrition were only twice those of the low phytic acid (lpa) beans that have a 90% lower phytic acid content compared to conventional beans. Proteome analysis revealed that sucrose metabolism and phosphate cycling are shifted in the lpa beans. We conclude that a tolerance to phosphate deficiency, particularly in terms of regulation of phosphate cycling and transport pathways, contributes to decreased seed phytic acid-to-Fe molar ratios.