Abstract
We have identified a homologue of the transcription factor ABI3 in Arabidopsis or the maize ortholog of ABI3, VP1 (ABI3/VP1), from Physcomitrella patens, which we termed PpABI3. PpABI3 showed high similarity with ABI3/VP1 in the B3 domain, which is a highly conserved domain among ABI3/VP1 homologues. The B1 and B2 domains, which are other conserved domains, were also observed in the PpABI3, although the similarities were not as high as that in B3. We performed transient assays in P. patens protonemal tissue as well as in barley aleurone cells using a wheat Em gene promoter. Over expression of PpABI3 resulted in the activation of the Em promoter in the absence of ABA in both cell types. However, co-bombardment of PpABI3 with barley ABI5, which is required for the ABI3/VP1-mediated transactivation of the Em promoter in barley, enhanced the activation of the Em promoter only in barley, not in P. patens.
