Plants have evolved a multilevel immune system to protect them against infection by a diverse range of pathogens. The first line of plant defense consists of the integral plasma membrane receptors, known as pattern-recognition receptors (PRRs), which recognize MAMP/PAMP or DAMP molecules. PRRs activate downstream signaling cascades that culminate in generation of the innate immune response, called PAMP-triggered immunity (PTI). The activation of PTI leads to the induction of basal defense responses, which include influx of Ca2+ in the cytosol, production of reactive oxygen species (ROS) and nitric oxide, activation of mitogen-activated protein kinase cascades, callose deposition, stomatal closure, phytoalexins biosynthesis, defence hormone biosynthesis and transcriptional induction of a large suite of defence-related genes.