Phytate boosts arsenic accumulation in hyperaccumulator Pteris vittata from contaminated soil by inducing root...

Phytate (myo-inositol hexakisphosphate) is an abundant organic phosphorus (P) in soil but unavailable to most plants. Arsenic-hyperaccumulator Pteris vittata can effectively utilize phytate under hydroponics, but how it works in soil remains unclear as phytate is bound strongly to soil. Here, we investigated the mechanisms how P. vittata uses soil phytate by quantifying plant nutrient uptake, phytase activity in root exudates and rhizosphere, rhizosphere P and As availability, and gene expressions of phytases and P-transporters. Pteris vittata was grown for 8-week in As-contaminated soil containing 60 mg kg^-1 As and 100 mg kg^-1 Na-phytate-P (soluble) or Ca-phytate-P (insoluble), with 20 mg kg^-1 soluble-P and no-P addition as adequate-P and low-P controls. Compared to adequate-P, phytate treatment increased P. vittata biomass by 23-33% via efficient P acquisition and enhanced uptake of Ca (13-17%), Fe (12-139%), and As (28-42%). P. vittata acquired phytate through phytase-mediated hydrolysis, which was supported by 54-96% greater phytase activities in P. vittata root exudates and rhizosphere, 1.8-fold greater rhizosphere available P, and 1.3-5.8 fold greater expressions of phytases PvPhy1 and PvPAP1 in P. vittata roots. Rhizosphere As availability was 9-18% greater in the Na-phytate than Ca-phytate treatment, which increased frond As by 11% and plant biomass by 8%. The greater As accumulation in the phytate treatments was attributed to 1.2-3.5 fold upregulation of P transporters PvPht1;2-1;4. We conclude that P. vittata efficiently utilizes phytate as the sole P source in soil, providing opportunities for effective phytoremediation in As-contaminated soil and effective phytate-P utilization for crop production in agricultural soil.