Abstract
ABI1 gene, which encodes a type 2C protein phosphatase (PP2C), functions as a negative regulator of the ABA-signaling in Arabidopsis. We have indicated that the moss Physcomitrella patens also conserves the PP2C-mediated ABA-signaling pathway, and have identified an ABI1 homologous gene, PpABI1 from P. patens. From the transient assay of P. patens, PpABI1 was suggested to be a negative regulator of the ABA-signaling. Here we analyzed the in vivo function of PpABI1 by gene targeting. ABA application is known to increase the freezing tolerance of P. patens protonemata in a dose-dependent manner. Protonemata of PpABI1 disruptant (PpABI1 KO) showed 2 times higher freezing tolerance than the wild type at 0.1µM ABA concentration. PpABI1 KO was more sensitive to exogenously applied ABA, as judged by the redifferentiation of protonemal cells into brood cells. These results clearly show that PpABI1 functions as a negative regulator of ABA-signaling in P. patens.
