Nitric Oxide in Plant Functioning: Metabolism, Signaling, and Responses to Infestation with Ecdysozoa Parasites

SIMPLE SUMMARY: Nitric oxide (NO) is a key molecule that has an important role in the plant life cycle. It mediates a range of physiological processes and responses to stresses (e.g., drought, salinity, or parasite invasion). Despite many studies, knowledge about NO involvement in these processes is incomplete. This review describes the influence of NO on physiological and biochemical processes and gene expression. It thoroughly discusses the interaction network of NO and other molecules in plant cells. Moreover, it highlights mechanisms of NO-dependent defense response against infestation with Ecdysozoa species, like nematodes, insects, and arachnids. ABSTRACT: Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological processes in plants, including responses to biotic and abiotic stresses. Changes in endogenous NO concentration lead to activation/deactivation of NO signaling and NO-related processes. This paper presents the current state of knowledge on NO biosynthesis and scavenging pathways in plant cells and highlights the role of NO in post-translational modifications of proteins (S-nitrosylation, nitration, and phosphorylation) in plants under optimal and stressful environmental conditions. Particular attention was paid to the interactions of NO with other signaling molecules: reactive oxygen species, abscisic acid, auxins (e.g., indole-3-acetic acid), salicylic acid, and jasmonic acid. In addition, potential common patterns of NO-dependent defense responses against attack and feeding by parasitic and molting Ecdysozoa species such as nematodes, insects, and arachnids were characterized. Our review definitely highlights the need for further research on the involvement of NO in interactions between host plants and Ecdysozoa parasites, especially arachnids.