Protein kinases play important role in signal transduction as well as participate in regulatory functions during different conditions throughout the phyla. These are subfamily of serine/threonine kinases which plays pivotal role as metabolite sensors which constantly checks balance of demand and supply of energy by metabolically active cells. Among all protein kinases, sucrose nonfermenting-1 related kinase-1 (SnRKs) acts as metabolic sensors in plants. These kinases are evolutionary conserved in all eukaryotes from budding yeast (SNF1) to mammal (AMP activated protein kinase AMPK). Plant SnRKs regulates transcriptional and metabolic programming of cells to promote tolerance against biotic and abiotic stress partially through the general repression of anabolism and an induction of catabolic processes. SnRKs divided in to three subfamilies: SnRK1, SnRK2, and SnRK3. SnRK1 kinases act as a central regulatory component to control metabolism for example carbohydrate, lipid and fatty acid uptake and regulation. It is well established that SnRK2 and SnRK3 cannot fulfill SnRK1 function hence they having similarity in target reorganization. SnRK1 generally functions as heterotrimeric complex having a-catalytic subunit and P,y-regulatory subunits. Some aspects for the role of SnRK1 kinase that control the fundamental issues have yet remained elusive. In this chapter, we will discuss about the structural, functional as well as regulatory aspects of SnRK1 and its upstream and downstream components along with its role in pathogen defense response.