Catalytic subunit of the AMP-activated protein kinase complex also known as the SNF1 kinase complex (Snf1c), a central regulator of cellular energy homeostasis, which, in response to a fall in intracellular ATP levels, activates energy-producing pathways and inhibits energy-consuming processes (By similarity). The complex phosphorylates histone H3 to form H3S10ph, which promotes H3K14ac formation, leading to transcriptional activation through TBP recruitment to the promoters (By similarity). Activates the expression of the galactose oxidase (GOA) gene and of several cell wall-degrading enzymes (CWDEs) such as pectate lyase, xylanase and glucanase (PubMed:28132080). Plays an important role in sudden death syndrome (SDS) by controlling the colonization of the infected roots (PubMed:28132080). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Component of the AMP-activated protein kinase complex also known as the SNF1 kinase complex (Snf1c), a heterotrimeric complex composed of a catalytic subunit alpha and 2 regulatory subunits beta and gamma (By similarity). Nuclear translocation occurs under nitrogen and glucose starvation conditions (By similarity). The regulatory domain (RS) also called auto-inhibitory domain (AID) inhibits kinase activity of the protein kinase domain (KD) (By similarity). The ubiquitin-associated domain (UBA) localized within the AID dampens kinase activation, probably by restraining alpha-gamma associations (By similarity). Impairs the expression of the galactose oxidase gene which abolishes galactose utilization and causes poor growth on xylose, arabinose and sucrose (PubMed:28132080). Impairs severely the ability to cause sudden death syndrome (SDS) on challenged soybean plants through preventing to colonize the xylem vessels and phloem tissue during infection (PubMed:28132080). Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. SNF1 subfamily.