A characterization of the response to auxin of the small GTPase, Rha1

Using the transgenic lines harboring GFP-Rha1 fused gene, we demonstrated that the Arabidopsis Rab5 homolog, Rha1 localized on the plasma membrane and endosomes in root epidermal cells and root hairs. Rha1 was accumulated to large dispatches under the vesicle transport inhibitor, brefeldin A (BFA) treatment. The distribution of Rha1 overlapped with the endocytic tracer marker, FM4-64, with or without BFA treatment demonstrates that Rha1 is involved in the endocytic pathway. Auxin could induce the expression of Rha1 in the RNA and protein levels. The subcellular localization of Rha1 also was affected by auxin treatment, IAA induced basal and apical localization and 1-NAA induced cytoplasmic distribution in root epidermal cells. In addition, over-expression of Rha1 reduced the sensitivity to BFA and NPA. These results together with the tissue-specific expression patterns of Rha1 in wild type plants, aux1 and eir1 mutants suggest that Rha1 is probably involved in auxin signal transduction.