Abstract
Signaling through heterotrimeric G-proteins is highly conserved among divergent eukaryotes. In plants, heterotrimeric G-proteins play an essential role in auxin, abscisic acid (ABA), and sugar response. If G-protein-coupled receptors (GPCR) bind their ligands, subunits of heterotrimeric G-proteins dissociate from each other and regulate activities of other proteins, thus mediating signaling from GPCR to downstream pathways. In plants, however, there have been few reports on factors regulated by heterotrimeric G-proteins. In this study, we performed yeast two-hybrid screening and identified a bZIP transcription factor VIP1 as a novel interacting partner of Arabidopsis heterotrimeric G protein beta (AGB1). AGB1-VIP1 interaction in planta was studied by the BiFC assay, and it was suggested that the interaction occurred in the nucleus. When VIP1 was expressed constitutively in Arabidopsis under the control of the CaMV35S promoter, seed germination was severely inhibited in the presence of NaCl, ABA, or glucose. AGB1 was known to be a negative regulator of ABA signaling. Taken together, our results propose possibility that VIP1 participates in the ABA signaling pathway mediated by AGB1.
