Small Signals Lead to Big Changes: The Potential of Peptide-Induced Resistance in Plants

Abstract

The plant immunity system is being revisited more and more and new elements and roles are attributed to participating in the response to biotic stress. The new terminology is also applied in an attempt to identify different players in the whole scenario of immunity: Phytocytokines are one of those elements that are gaining more attention due to the characteristics of processing and perception, showing they are part of a big family of compounds that can amplify the immune response. This review aims to highlight the latest findings on the role of phytocytokines in the whole immune response to biotic stress, including basal and adaptive immunity, and expose the complexity of their action in plant perception and signaling events.

Keywords: induced resistance; peptides; phytocytokines; plant immunity; priming.

Figure 1

The natural function of defense peptides vs. Peptide-Induced Resistance. Example with the perception of the peptide Pep1 (A) Cellular responses against a pathogenic fungi infection. 1, Pathogen penetration in the cell is perceived by plant membrane receptors. 2, Intracellular signaling and defense responses are produced, including ROS production, the opening of ion and Ca²⁺ channels, and MAPK cascade activation that lead to downstream transcriptional reprogramming and defense compounds production. In parallel, peptide precursors are synthesized and phytocytokines are released. 3, mature peptides are released to the apoplast where they are perceived by damaged and adjacent cells. 4, phytocytokines trigger the amplification of defense responses. 5, the battery of defensive elements impairs pathogen success. (B) Mechanisms of Peptide-IR. 1, cell membrane receptors perceive the exogenously applied phytocytokine. 2, Immune responses are activated as in (A). 3, an invading fungal pathogen is perceived. 4, the plant is already prepared to counteract the infection, displaying a faster and stronger defense response that leads to enhanced resistance.