Cyclic nucleotide gated channels and related signaling components in plant innate immunity

Although plants lack the mobile sentry cells present in animal innate immune systems, plants have developed complex innate immune reactions triggering basal resistance and the hypersensitive response (HR). Cytosolic Ca(2+) elevation is considered to be an important early event in this pathogen response signal transduction cascade. Plasma membrane (PM)-localized cyclic nucleotide gated channels (CNGCs) contribute to the cytosolic Ca(2+) rise upon pathogen perception. Recent work suggests that some PM-localized leucine-rich-repeat receptor-like kinases (LRR-RLKs) may be involved in the perception of pathogen associated molecular pattern molecules and triggering some pathogen responses in plants, some of these LRR-RLKs might have cyclic nucleotide cyclase activity. The recognition of pathogens may be connected to cyclic nucleotide generation and the activation of CNGCs, followed by cytosolic Ca(2+) increase and downstream signaling events (possibly involving nitric oxide, reactive oxygen species (ROS), calmodulin (CaM), CaM-like protein (CML) and protein kinases). Notably, CaM or CML could be the crucial sensor downstream from the early Ca(2+) signal leading to nitric oxide (NO) production during plant innate immune responses.