Domain fusion between SNF1-related kinase subunits during plant evolution

Members of the conserved SNF1/AMP-activated protein kinase (AMPK) family regulate cellular responses to environmental and nutritional stress in eukaryotes. Yeast SNF1 and animal AMPKs form a complex with regulatory SNF4/AMPK gamma and SIP1/SIP2/GAL83/AMPK beta subunits. The beta -subunits function as target selective adaptors that anchor the catalytic kinase and regulator SNF4/gamma -subunits to their kinase association (KIS) and association with the SNF1 complex (ASC) domains. Here we demonstrate that plant SNF1-related protein kinases (SnRKs) interact with an adaptor-regulator protein, AKIN beta gamma, in which an N-terminal KIS domain characteristic of beta -subunits is fused with a C-terminal region related to the SNF4/AMPK gamma proteins. AKIN beta gamma is constitutively expressed in plants, suppresses the yeast Delta snf4 mutation, and shows glucose-regulated interaction with the Arabidopsis SnRK, AKIN11. Our results suggest that evolution of AKIN beta gamma reflects a unique function of SNF1-related protein kinases in plant glucose and stress signalling.