Arsenic Uptake and Metabolism in Mycorrhizal As-Hyperaccumulator <i>Pteris vittata</i>: Symbiotic P Transporters and As Reductases

Arbuscular mycorrhiza (AM) often protect host plants from As accumulation under arsenic stress; however, the opposite is true for the As-hyperaccumulator <i>Pteris vittata</i>. With non-hyperaccumulator <i>Pteris ensiformis</i> as a comparison, the AM colonization, P and As uptake, and genes associated with As metabolism were investigated in <i>P. vittata</i> after growing 60-day with <i>Rhizophagus irregularis</i> inoculation under 0 (As₀), 10 (As₁₀), or 100 μM As (As₁₀₀) treatments. Based on the As-induced increase in AM colonization (up to 21%), AM symbiosis promoted <i>P. vittata</i> growth by 24% and frond P content by 22% in the AM+As₁₀₀ treatment than As₁₀₀ treatment. These increases corresponded to 4.2- to 5.4-fold upregulation in symbiotic P transporter <i>RiPT1</i>/<i>7</i> in AM fungi and <i>PvPht1;6</i> in <i>P. vittata</i> roots, which probably supported 37% greater As accumulation at 4980 mg kg^-1 in the fronds. Besides total As, enhanced arsenate reduction was evidenced by 19% greater arsenite and 15-fold upregulation of fungal arsenate reductase <i>RiArsC</i> in mycorrhizal roots. Further, the 2.1-fold upregulation of arsenite antiporters <i>PvACR3/3;3</i> contributed to greater arsenite translocation to and sequestration in the fronds. Unlike <i>P. ensiformis</i> symbiont, which suffers from As stress, the mycorrhiza-specific P transporters (RiPT1/7 and PvPht1;6), arsenate reductases (RiArsC and PvHAC2), and arsenite antiporters (PvACR3/3;3) all benefited AM symbiosis and As accumulation in <i>P. vittata</i>.