Phytate-Mediated Arsenic Hyperaccumulation in <i>Pteris vittata</i> : Synthesis, Sequestration, and Exudation

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