Molecular mechanism for the inhibition of a critical component in the Arabidopsis thaliana abscisic acid signal transduction pathways, SnRK2.6, by the protein phosphatase ABI1.

Tsinghua University, China.
Subclass III SnRK2s (SnRK2.6/2.3/2.2) are the key positive regulators of ABA (abscisic acid) signal transduction in Arabidopsis thaliana. The kinases, activated by ABA or osmotic stress, phosphorylate stress-related transcription factors and ion channels, which ultimately leads to the protection of plant from dehydration or high salinity. In the absence of stressors, SnRK2s are subject to negative regulation by the group A PP2Cs, while the underlying molecular mechanism remains to be elucidated. Here we report the crystal structure of the kinase domain of SnRK2.6 at 2.6 angstrom resolution. Structure-guided biochemical analyses identified two distinct interfaces between SnRK2.6 and ABI1. Structural modeling suggested that the two interfaces lock SnRK2.6 and ABI1 in an orientation such that the activation loop of SnRK2.6 is posited to the catalytic site of ABI1 for dephosphorylation. These studies revealed the molecular basis for PP2Cs-mediated inhibition of SnRK2s and provided important insights into the downstream signal transduction of ABA.
Unknown Nov. 16, 2011; 0(0); [PUBMED:22090030]
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