Pattern Recognition Receptors in Plant Immunity

Plant innate immunity is an advanced defense system to counteract pathogenic stresses. It relies on the recognition of microbial invasion through cell surface-localized pattern recognition receptors (PRRs) and intracellular nucleotide-binding domain leucine-rich repeat receptors (NLRs). PRRs form multiprotein complexes composed of transmembrane and cytosolic kinases, while NLR proteins serve as intracellular receptors, directly or indirectly detecting pathogen effector proteins and alterations induced by them in host plants. Traditionally, PRRs are associated with pattern-triggered immunity (PTI), whereas NLRs are linked to effector-triggered immunity (ETI). Activation of PRRs and NLRs occurs through different mechanisms, stimulated by ligands present in different subcellular compartments. However, evidence suggests that signaling initiated by PRRs and NLRs converges into conjoined pathways that significantly impact immune responses during abiotic stress. Therefore, it is important to comprehend the molecular mechanisms of the plant's innate immune system, to extend its defensive action to a wide variety of plant challenges ranging from pathogens to climatic stresses. Here, a broad review of plant immunity is provided, with relevance to PRRs and NLRs. Recent breakthroughs in the understanding of PRRs and NLRs, including their stress recognitional patterns and interplay are discussed with the aim of revealing the intricate mechanisms underlying plant innate immunity in response to biotic and abiotic stresses. The modulation of plant innate immunity in the context of climatic changes is explored. Identification of both common and specific elements of the immunity signaling in plants will enable the composition of new targets of the plant immune system to combat a wide array of stresses during the global climatic challenges.