Characteristics, Roles and Applications of Proteinaceous Elicitors from Pathogens in Plant Immunity

Abstract

In interactions between pathogens and plants, pathogens secrete many molecules that facilitate plant infection, and some of these compounds are recognized by plant pattern recognition receptors (PRRs), which induce immune responses. Molecules in both pathogens and plants that trigger immune responses in plants are termed elicitors. On the basis of their chemical content, elicitors can be classified into carbohydrates, lipopeptides, proteinaceous compounds and other types. Although many studies have focused on the involvement of elicitors in plants, especially on pathophysiological changes induced by elicitors in plants and the mechanisms mediating these changes, there is a lack of up-to-date reviews on the characteristics and functions of proteinaceous elicitors. In this mini-review, we provide an overview of the up-to-date knowledge on several important families of pathogenic proteinaceous elicitors (i.e., harpins, necrosis- and ethylene-inducing peptide 1 (nep1)-like proteins (NLPs) and elicitins), focusing mainly on their structures, characteristics and effects on plants, specifically on their roles in plant immune responses. A solid understanding of elicitors may be helpful to decrease the use of agrochemicals in agriculture and gardening, generate more resistant germplasms and increase crop yields.

Keywords: NLPs; elicitin; elicitors; harpin; immune response.

Figure 1

The BAK1–RLP23–SOBIR1 complex recognizes NLP peptides and mediates immune responses. RLP23 and SOBIR1 complex together and are isolated from BAK1 without NLP peptide perception. NLP peptides from pathogens are perceived by RLP23 and form tripartite receptor complexes of BAK1–RLP23–SOBIR1, which initiate downstream immune responses, including ROS burst, MAPK cascade activation, PR gene transcription and ethylene production. NTCD4, an LRR-only protein, promotes NLP oligomerization that induces pore formation on the plasma membrane, which is cytotoxic and triggers cell death.