Two Half-Size ATP-Binding Cassette Transporters Are Implicated in Aluminum Tolerance in Soybean

Aluminum (Al) toxicity severely restricts plant production in acidic soils. ATP-binding cassette (ABC) transporters participate in plant tolerance to various environmental stresses. However, ABC transporters implicated in soybean Al tolerance are still rare. Here, we functionally characterized two half-size ABC transporters (GmABCB48 and GmABCB52) in soybean. Expression analysis showed that <i>GmABCB48</i> and <i>GmABCB52</i> were induced only in the roots, especially in the root tips. Both GmABCB48 and GmABCB52 were localized at the plasma membrane. Overexpression of <i>GmABCB48</i> or <i>GmABCB52</i> in <i>Arabidopsis</i> reduced Al accumulation in roots and enhanced Al tolerance. However, expression of <i>GmABCB48</i> or <i>GmABCB52</i> in yeast cells did not affect Al uptake. Furthermore, transgenic lines expressing <i>GmABCB48</i> or <i>GmABCB52</i> had lower Al content in root cell walls than wild-type plants under Al stress. Further investigation showed that the Al content in cell wall fractions (pectin and hemicellulose 1) of transgenic lines was significantly lower than that of wild-type plants, which was coincident with the changes of pectin and hemicellulose 1 content under Al exposure. These results indicate that GmABCB48 and GmABCB52 confer Al tolerance by regulating the cell wall polysaccharides metabolism to reduce Al accumulation in roots.