Negative Regulation Of Abscisic Acid Signaling By The Brassica Oleracea ABI1Ortholog

ABA (Abscisic Acid) is an important plant hormone, which participates in response tostress and modulation of plant growth and development, including seed germination, seeddormancy, plant growth and stomatal closure and so on. As one of the most important keyfactors of plant drought, high salt and other environmental stress responses, significantprogresses in ABA signaling have been achieved during the past decade. The discovery ofABA receptors and demonstration of the core signal transduction regulatory network indicatethat PP2C (Type-2C Protein Phosphatases) is a key adaptor between ABA receptors anddownstream kinases. ABI1(ABA INSENSITIVE1), one representative member of plantPP2C, is involved in plant growth and development as well as responses to environmentalstresses.In the current study, the homologous gene of ABI1was cloned in cabbage (Brassicaoleracea) and functional analyzed. The cDNA of BolABI1is1281nt long, encoding a proteinof426amino acids. Sequence alignment revealed that BolABI1has the same motifarrangement as ABI1, including a PP2C domain, an ABA box and a SnRK3interactiondomain. Expression of BolABI1occurs mainly in young leaves and is induced by droughtstress. Seed germination of transgenic lines overexpressing BolABI1(Col-0::Flag-BolABI1) isinsensitive to ABA. Subcellular localization and phosphatase assays reveal that BolABI1ispredominantly localized in the nucleus and harbors phosphatase activity. Furthermore,BolABI1interacts with a homolog of OST1(OPEN STOMATA1) in Brassica oleracea(BolOST1) and can dephosphorylate ABI5(ABA Insensitive5) in vitro.Overall, these results suggest that BolABI1is a functional PP2C-type proteinphosphatase that is involved in the negative modulation of the ABA signaling pathway.