The role of solute transporters in aluminum toxicity and tolerance

Abstract

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.

γ-Aminobutyrate (GABA) Regulated Plant Defense: Mechanisms and Opportunities

“…The accumulation of free aluminum (Al 3+ ) ions in the soil solution under low pH limits plant growth and productivity [ 124 ]. Ramesh et al [ 101 ] have monitored malate efflux in roots of near-isogenic, Al 3+ tolerant (ET8) and sensitive (ES8) lines of wheat.…”

“…While the GABA level is higher in ET8 than in ES8 under acidic conditions, Al 3+ reduces the GABA level in both lines to similar levels. This suggests that high endogenous GABA inhibits the activity of TaALMT1 in the absence of Al 3+ , and that both malate and GABA are exported from the cytosol when TaALMT1 is Al 3+ activated, resulting in the sequestration of Al 3+ and modulation of the plant sensitivity to Al 3+ [ 102 , 124 ]. Table 2 summarizes various examples wherein ALMT1 overexpression enhances the efflux of malate in response to Al 3+ treatment under acidic conditions [ 101 , 125 , 126 , 127 , 128 ].…”

“…Table 3 briefly summarizes examples wherein genetic manipulation of endogenous GABA modifies biotic stress resistance. For example, transgenic tobacco and Arabidopsis plants with elevated GABA levels are more resistant to infection by Agrobacterium and Pseudomonas than WT plants [ 123 , 124 ], as well to predation by insect larvae and root-knot nematode [ 119 , 120 , 121 , 122 ]. In contrast, tomato plants with extremely low GABA levels are more susceptible to infection by Ralstonia [ 128 ].…”

Recent Advances in Understanding Mechanisms of Plant Tolerance and Response to Aluminum Toxicity

“…Studies have showed that the transportation of other ions could also alleviate Al toxicity [19]. For example, Ca 2+ serves as an essential second messenger to modulate developmental plasticity in plants, which reduces the concentration of active Al and fixation of P under Al stress [111,112]. Treatment with higher Ca 2+ concentration alleviates Al-induced inhibition of root growth, which is attributed to higher cytosolic Ca 2+ concentrations through specific Ca 2+ signatures triggering downstream responses [113].…”

Strategies of tolerance reflected in two North American maple genomes

“…Downregulation of cellulose and upregulation of callose, oxidative stress, hormones, and DNA damage signaling all result in root growth inhibition (Sade et al, 2016). The plasma membrane is another frequent target, where Al disrupts membrane potential and membrane-bound solute transporters, affecting symplastic and apoplastic concentrations (Kar et al, 2021). Damage within proteins and DNA reduces enzymatic activity and can trigger cell cycle checkpoints.…”