Abstract
Arabidopsis thaliana ABI1, which encodes a type-2C Ser/Thr protein phosphatase (PP2C), is a negative regulator of ABA-signaling pathway. The abi1-1 is a dominant mutant of ABI1 that carries an amino acid substitution (Gly to Asp) in the catalytic domain, and strongly blocks ABA signaling. Multiple ABI1-interacting proteins have been isolated, but none of these interactions are able to explain the dominant effect of abi1-1 in ABA signaling. Previously we demonstrated that the PP2C-mediated ABA signaling is evolutionarily conserved in the moss Physcomitrella patens. The protonemata of P. patens consist of only two cell types, and ABA response does occur uniformly in protonemal cells. Thus, by exploiting the feature of the protonemata, we started to identify interacting proteins of PpABI1A from P. patens using a yeast-two-hybrid system. We obtained about 250 positive clones from screening of 700,000 clones. We are analyzing these clones, and some of the results will be discussed.
