Editorial: Control of Plant Pathogens by Biogenic Elicitors and Possible Mechanisms of Action

Elicitors of biological origin, especially those that are able to control plant pathogens by induction of plant systemic resistance are being intensively investigated because of their great potential for crop protection and environmental compatibility. Since the range of induced defense responses can depend on the elicitor used, the plant treated and the target pathogen, a detailed study of the modes of action of biogenic elicitors is required prior to their use. In this context, an important aim of the Research Topic on Control of plant pathogens by biogenic elicitors and possible mechanisms of action was a better understanding of the mechanisms underlying the protective effect of microorganisms with a potential or already established role in biocontrol. Interestingly, works included in the topic report that a biocontrol agent is simultaneously able to activate both SAR and ISR defense pathways in the same plant (e.g., Salas-Marina et al.; Song et al.). Thus, tomato root colonization with the arbuscular mycorrhizal fungus Funneliformis mosseae induced a range of plant defense reactions, and primed defense responses, including the activation of some enzymes and the up-regulation of PR genes associated with SAR upon challenge with Alternaria solani. At the same time, it was also shown that JA-dependent signaling was necessary for mycorrhiza-primed systemic resistance to this pathogen (Song et al.). Plant disease resistance is triggered by various elicitors, which are widely presented in pathogenic and non-pathogenic fungi, bacteria and oomycetes. Biogenic elicitors (glycoproteins, lipids, or oligosaccharides) as well as microbial proteins and peptides triggering defense responses play an important role in the development of local and systemic resistance. In the current research topic, several publications confirm the importance of such proteins for plant-mediated interactions of biocontrol fungi with soil or foliar pathogens of various life styles. They report both common features and individual specificity concerning the mechanisms of action of various proteinaceous elicitors. For instance, colonization of plant roots with saprophytic Fusarium oxysporum or Trichoderma strains protects tomato against vascular wilt and other diseases via distinct mechanisms including induction of local and systemic resistance. Proteins, such as CS20EP produced by F. oxysporum strain CS-20 (Shcherbakova et al.) as well as Sm1 and Epl1 from Trichoderma spp. (Salas-Marina et al.) strongly contribute to the activation of defense-responsive genes in the pretreated plants. Experiments on systemic tomato protection with wild, epl1-and sm1-deletion or overexpression strains against necrotrophic (A. solani, Botrytis cinerea) and hemibiotrophic (Pseudomonas syringae pv. tomato) pathogens …