The role of solute transporters in aluminum toxicity and tolerance.

The prevalence of aluminum ions (Al3+ ) under acidic soil conditions inhibits primary root elongation and hinders plant growth and productivity. Al3+ alters the membrane potential, displaces critical ions in the apoplast and disrupts intracellular ionic concentrations by targeting membrane-localized solute transporters. Here, we provide an overview of how Al3+ affects the activities of several solute transporters especially in the root. High Al3+ level impairs the functions of potassium (K+ ), calcium (Ca2+ ), magnesium (Mg2+ ), nitrate (NO3 - ) and ammonium (NH4 + ) transporters. We further discuss the role of some key transporters in mediating Al tolerance either by exclusion or sequestration. Anion channels responsible for organic acid efflux modulate the sensitivity to Al3+ . The ALUMINUM ACTIVATED MALATE TRANSPORTER (ALMT) and MULTIDRUG AND TOXIC COMPOUND EXTRUSION (MATE) family of transporters exude malate and citrate, respectively, to the rhizosphere to alleviate Al toxicity by Al exclusion. The ABC transporters, aquaporins and H+ -ATPases perform vacuolar sequestration of Al3+ , leading to aluminum tolerance in plants. Targeting these solute transporters in crop plants can help generating aluminum-tolerant crops in future.