Phytate-Mediated Arsenic Hyperaccumulation in Pteris vittata : Synthesis, Sequestration, and Exudation

Phytate enhances arsenic metabolism in As-hyperaccumulator Pteris vittata, but the underlying mechanisms remain unclear. Using P. multifida and P. ensiformis as comparisons, we investigated the plant growth, As/P uptake, and phytate synthesis, sequestration, and exudation in P. vittata under 10-100 μM As exposure. The expressions of P transporters Pht1;2-1;4, phytate synthesis genes including myo-inositol 3-phosphate synthase (MIPS), myo-inositol monophosphatase (IMP), and 2-phosphoglyceric acid kinase (2-PGK), and phytate transporter multidrug resistance-associated protein 5 (MRP5) were analyzed. After 3 weeks of growth, P. vittata accumulated the greatest As in the fronds at 155-3098 mg kg^-1, with biomass being increased by 9.8-63%. While greater expression of PvPht1;2/1;4 helped P. vittata maintain stable plant P contents at 3005-3552 mg kg^-1, PmPht1;2/1;4 and PePht1;2/1;4 expressions were reduced by 10-55%. Arsenic exposure enhanced phytate accumulation in P. vittata by upregulating phytate synthesis genes MIPS, IMP, and 2-PGK and phytate transporter gene MRP5 by 1.3-1.7-fold, increasing phytate contents by 1.1-2.1-fold to 69.2-371 mg kg^-1. Further, P. vittata increased phytate root exudation by 1.5-3.6-fold under As exposure, whereas P. multifida and P. ensiformis mainly exuded tartrate. In short, As-enhanced phytate metabolism in P. vittata is unique and contributes to its superior As-accumulation ability, showing implication for phytoremediation of As-contaminated soils.