Regulation of Arabidopsis MAPKKK18 by ABI1 and SnRK2, components of the ABA signaling pathway

Abstract

The plant hormone abscisic acid (ABA), a key regulator in many crucial developmental and physiological processes, recruits diverse components into precisely regulated signaling network. We recently discovered that MAPKKK18, an ABA-activated kinase, is regulated by the protein phosphatase type 2C (PP2C) ABI1 and the kinase SnRK2.6, both components of the ABA core signaling pathway. ABI1 acts to inhibit MAPKKK18 kinase activity, but also affects MAPKKK18 protein turnover via the ubiquitin-proteasome pathway. SnRK2.6 kinase also seems to be important for the regulation of MAPKKK18 function. In this review we summarize the mechanisms that are exclusively involved in MAPKKK18 kinase regulation and that ensure specificity in its activation.

Keywords: ABA signaling; ABI1; Arabidopsis thaliana; MAP kinase cascade; MAPKKK18; PP2C; SnRK2; UPS.

Figure 1.

MAPKKK18 interacts with the SnRK2.6 kinase. (A) Pull-down assay to verify the interaction beteween SnRK2.6 and MAPKKK18. Input lines represent total SnRK2.6. Recombinant His- MAPKKK18, pre-coupled to Ni-NTA agarose, was incubated with recombinant GST-SnRK2.6. GST- and His-tagged proteins were detected (IB) using anti-GST and anti-His tag antibodies, respectively. (B) SnRK2.6 and MAPKKK18 proteins interact within the nucleus. Cytoplasmic interaction around the nucleus is present in about 10% of protoplasts. BiFC analysis in Arabidopsis protoplasts transiently expressing full-length SnRK2.6 and MAPKKK18 fused to cECFP or nVenus, respectively. RFPtag-CBP20 was used as both transformation control and marker of nuclear localization. Scale bar: 20 μm.