Research progresses in aluminum tolerance mechanisms in plants

Aluminum toxicity is one of the most deleterious factors limiting crop production on acid soils.Hence,understanding the mechanisms and genes conferring tolerance to aluminum toxicity has been the research highlight over the past decade.Combining with the latest research results,we briefly reviewed the current understanding of the physiological,genetic,and molecular basis for plant aluminum tolerance.Resistant mechanism to Al stress has been classified as exclusion mechanism that excludes Al from entering root apex and internal tolerance mechanism that allows the plant to tolerate Al accumulation in root and shoot symplasm.Physiologically,although organic acids efflux is an important mechanism whereby some plants exhibit high Al resistance,other mechanisms such as phenolic compounds secretion and immobilization of aluminum with phosphorous in root apoplast also operate in plants.The internal tolerant mechanism was mainly achieved by forming non-phytotoxic Al-organic acid chelator and compartmentation in vacuole.The genetic architecture of tolerance was variable,being monogenic in some species such as wheat but polygenic in others such as maize.Recently,the first Al-tolerant gene ALMT1 controlling Al-regulated malate efflux from plant roots was cloned and transgene ALMT1 plants showed high Al tolerance.A better understanding will open up new avenues of physiological and molecular research that will in turn greatly advance our understanding of these tolerance mechanisms.Additionally,these breakthroughs would provide new molecular resources for improving crop aluminum tolerance via both molecular-assisted breeding and biotechnology.