Abstract
Abscisic acid is a ubiquitous hormone that plays a central role in land plants'responses to environmental stresses. The molecular mechanisms of ABA responses have been revealed in higher plants. In contrast, the mechanisms of ABA responses in lower land plants are not well understood. In order to understand molecular mechanisms underlying ABA responses in bryophytes, we analyzed Marchantia polymorpha MpABI1, a homologue of ABSCISIC ACID INSENSITIVE 1 (ABI1) in Arabidopsis. MpABI1 encoded a protein phosphatase 2C (PP2C) with an N-terminal regulatory domain. Transient expression of MpABI1 in Physcomitrella patens resulted in suppression of ABA-induced gene expression. Furthermore, ABA-induced freezing tolerance was impaired in transgenic mosses expressing the PP2C domain of MpABI1. These results suggest that MpABI1 is a negative regulator of ABA responses and that the functions of PP2Cs in ABA signaling are conserved in land plants.
