Abstract
A plant-specific transcription factor ABI3/VP1 is expressed mainly in seeds, and plays an important role in seed maturation and dormancy. We have identified three copies of ABI3/VP1 homolog (designated as PpABI3A, PpABI3B and PpABI3C) from the moss Physcomitrella patens, which forms not seeds but spores. Although PpABI3A was partially able to complement the function of ABI3/VP1 in higher plants, the in vivo function of the PpABI3 gene in P. patens was yet to be elucidated. Here we report that PpABI3A, PpABI3B and PpABI3C were expressed though the life cycle of P. patens, in contrast to ABI3/VP1. The overexpressors of PpABI3A were more sensitive to ABA, and the triple knockout of PpABI3 genes was less sensitive to ABA, as judged by the protonemata growth on media containing ABA. These data strongly suggest that PpABI3 functions as a positive regulator of the ABA-signaling in vivo and regulates the protonemal growth.
