Plant Elicitor Peptides as Amplifiers of Immune Responses Against Biotic Stressors

Plants are continuously challenged by various pathogenic organisms and pests that threaten their existence. However, through millions of years of co-evolution, plants have acquired an array of defense mechanisms that enable them to withstand most biotic stresses effectively. Immunogenic signals perceived at the onset of an infection event trigger a cascade of defense responses within a plant. Some of these immunogenic signals originate externally, such as microbial immunogenic patterns or microbe-associated molecular patterns (MAMPs), which are recognized by pattern recognition receptors (PRR) localized in the plant cell membranes, initiating signaling cascades that induce defense responses. In addition, there are endogenous triggers, which may be constitutively expressed molecules or induced immunogenic factors, that stimulate the induction of immune responses. These induced endogenous immunogenic factors, known as phytocytokines, are detected by membrane-localized receptors (PEPRs) to modulate immune responses. Plant elicitor peptides (Peps) are a group of phytocytokines that amplify downstream signaling mechanisms by binding to receptors containing leucine-rich repeat domains, thereby initiating signaling cascades to reinforce pattern-triggered immunity (PTI), in response to various biotic challenges. Consequently, Peps have emerged as a focal point of research due to their pivotal role in modulating plant defense responses, offering potential applications in agriculture for enhancing plant resistance mechanisms through genetic manipulations and the commercial application of exogenous priming agents. This chapter provides an overview of the known classes of Peps, current insights into their modes of action, and their role in enhancing plant immunity.