EIR1, A ROOT-SPECIFIC PROTEIN INVOLVED IN AUXIN TRANSPORT, IS REQUIRED FOR GRAVITROPISM IN ARABIDOPSIS-THALIANA

The EIR1 gene of Arabidopsis is a member of a family of plant genes wi th similarities to bacterial membrane transporters. This gene is expre ssed only in the root, which is consistent with the phenotypes of the eir1 mutants-the roots are agravitropic and have a reduced sensitivity to ethylene. The roots of eir1 mutants are also insensitive to the ex cess auxin produced by alf1-1 and fail to induce an auxin-inducible ge ne in the expansion zone. Although they fail to respond to internally generated auxin, they respond normally to externally applied auxin. Ex pression of the EIR1 gene in Saccharomyces cerevisiae confers resistan ce to fluorinated indolic compounds. Taken together, these data sugges t that the EIR1 protein has a root-specific role in the transport of a uxin.