An ATP binding cassette transporter HvABCB25 confers aluminum detoxification in wild barley

Aluminum (Al) stress in acid soils is one of the major factors limiting crop productivity. ATP binding cassette (ABC) transporters have numerous roles in plants, but the link between ABCB protein subfamily and plant Al tolerance is still elusive. Here, we identified and characterized a novel tonoplast HvABCB25 in barley root cells. HvABCB25 was up-regulated in the transcriptome of Al-tolerant wild barley XZ16 under Al treatment and was highly Al-inducible in root tips. ABCB25 is originated from Streptophyte algae and evolutionarily conserved in land plants. Moreover, silencing HvABCB25 in Al-tolerant XZ16 led to significant suppression of Al tolerance as indicated by significantly reduced root growth and enhanced Al accumulation in root cells. Conversely, HvABCB25-overexpressed plants and Golden Promise showed similar Al content in whole roots and in cell sap, but the overexpression lines exhibited significantly higher Al-induced relative root growth and dry weight. Al florescence in cytosol of root cells were significantly less in overexpression lines than that in GP. These results indicated that overexpressing HvABCB25 may be responsible for Al detoxification via vacuolar Al sequestration in barley roots, providing useful insight into the genetic basis for a new Al detoxification mechanism towards plant Al tolerance in acid soils.