Abstract
Arabidopsis ABI1 encodes a type 2C protein phosphatase (Group A PP2C) that negatively regulates ABA signal transduction. We have established transgenic moss plants that lack genes for Group A PP2C. In normal condition, this transgenic plants showed growth inhibition, constitutive expression of ABA-responsive genes, and marked tolerances to desiccation and freezing, suggesting that ABA signaling is constitutively active in the transgenic plants. We also analyzed ABA responses of the transgenic plants in regard to accumulations of sugars and, boiling-soluble proteins, including a protein that is immunologically related to dehydrin. Surprisingly, the transgenic plants did not show any significant response to exogenously applied ABA, and the wild type exceeded the transgenic plants in the accumulation level of sugars and boiling-soluble proteins when ABA was applied at 10μM. These results suggest that P. patens Group A PP2C plays a major role in preventing activation of ABA signaling under normal condition, and also play a role in enhancing responses to higher concentration of ABA.
