Abstract
The plant hormones salicylic acid (SA) and jasmonic acid (JA) regulate defense mechanisms capable of overcoming different plant stress conditions and constitute distinct but interconnected signaling pathways. Interestingly, several other molecules are reported to trigger stress-specific defense responses to biotic and abiotic stresses. In this study, we investigated the effect of 14 elicitors against diverse but pivotal types of abiotic (drought) and biotic (the chewing insect Ascia monuste, the hemibiotrophic bacterium Pseudomonas syringae DC 3000 and the necrotrophic fungus Alternaria alternata) stresses on broccoli and Arabidopsis. Among the main findings, broccoli pre-treated with SA and chitosan showed the highest drought stress recovery in a dose-dependent manner. Several molecules led to increased drought tolerance over a period of three weeks. The enhanced drought tolerance after triggering the SA pathway was associated with stomata control. Moreover, methyl jasmonate (MeJA) reduced A. monuste insect development and plant damage, but unexpectedly, other elicitors increased both parameters. GUS reporter assays indicated expression of the SA-dependent PR1 gene in plants treated with nine elicitors, whereas the JA-dependent LOX2 gene was only expressed upon MeJA treatment. Overall, elicitors capable of tackling drought and biotrophic pathogens mainly triggered the SA pathway, but adversely also induced systemic susceptibility to chewing insects. These findings provide directions for potential future in-depth characterization and utilization of elicitors and induced resistance in plant protection.
Highlights
The plant hormones salicylic acid (SA) and jasmonic acid (JA) regulate defense mechanisms capable of overcoming different plant stress conditions and constitute distinct but interconnected signaling pathways
Based on a literature survey, 14 elicitor molecules that were shown to enhance stress tolerance by activation of the plant defense systems were selected: 1. Acibenzolar S-methyl (ASM), a fungicide that acts by activation of SAR22. 2. β-Aminobutyric acid (BABA), a non-protein amino acid that induces systemic resistance[23,24]
Azelaic acid (AzA), a nine-carbon dicarboxylic acid that serves as a mobile systemic acquired resistance (SAR) signal in the vascular sap and that confers local and systemic resistance to biotic stress[34,35]
Summary
The plant hormones salicylic acid (SA) and jasmonic acid (JA) regulate defense mechanisms capable of overcoming different plant stress conditions and constitute distinct but interconnected signaling pathways. Elicitors capable of tackling drought and biotrophic pathogens mainly triggered the SA pathway, but adversely induced systemic susceptibility to chewing insects. These findings provide directions for potential future in-depth characterization and utilization of elicitors and induced resistance in plant protection. The ISR is characterized by the induction of a faster and more effective response against biotic stress as the plant cells are activated prior to the stress by non-pathogenic rhizobacteria This concept is called priming[17] and was initially discovered in studies on the interplay of plants with beneficial soil microorganisms such as Pseudomonas fluorescence or Trichoderma sp[18]. The effect of 14 elicitor molecules was assessed on different types of stress encountered by plants, including drought, infestation with the chewing insect Ascia monuste, infection with the hemibiotrophic bacterium Pseudomonas syringae pv. Our data evidence that the induced drought tolerance is at least in part regulated via the SA pathway and that it is associated with stomata control
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