Characterization of an inducible C 2 H 2 ‐type zinc finger transcription factor Vu STOP 1 in rice bean ( Vigna umbellata ) reveals differential regulation between low pH and aluminum tolerance mechanisms

The rice bean ( Vigna umbellata ) root apex specifically secretes citrate through expression activation of Vigna umbellata Multidrug and Toxic Compound Extrusion 1 ( Vu MATE 1 ) under aluminum (Al 3+ ) stress. However, the underlying mechanisms regulating Vu MATE 1 expression remain unknown. We isolated and characterized a gene encoding Sensitive to Proton Rhizotoxicity1 ( STOP 1)‐like protein, Vu STOP 1 , from rice bean. The role of Vu STOP 1 in regulating Vu MATE 1 expression was investigated using the yeast one‐hybrid assay. We characterized the function of Vu STOP 1 in Al 3 + ‐ and H + ‐tolerance using in planta complementation assays. We demonstrated that Vu STOP 1 has transactivation potential. We found that Vu STOP 1 expression is inducible by Al 3+ and H + stress. However, although Vu STOP 1 binds to the promoter of Vu MATE 1 , the inconsistent tissue localization patterns of Vu STOP 1 and Vu MATE 1 preclude Vu STOP 1 as the major factor regulating Vu MATE 1 expression. In addition, when a protein translation inhibitor increased expression of Vu STOP 1 , Vu MATE 1 expression was inhibited. In planta complementation assay demonstrated that Vu STOP 1 could fully restore expression of genes involved in H + tolerance, but could only partially restore expression of At MATE . We conclude that Vu STOP 1 plays a major role in H + tolerance, but only a minor role in Al 3+ tolerance. The differential transcriptional regulation of Vu STOP 1 and Vu MATE 1 reveals a complex regulatory system controlling Vu MATE 1 expression.