Abstract
The induction of general plant defense responses following the perception of external elicitors is now regarded as the first level of the plant immune response. Depending on the involvement or not of these molecules in pathogenicity, this induction of defense is called either Pathogen-Associated Molecular Pattern (PAMP) Triggered Immunity or Pattern Triggered Immunity—both abbreviated to PTI. Because PTI is assumed to be a widespread and stable form of resistance to infection, understanding the mechanisms driving it becomes a major goal for the sustainable management of plant-pathogen interactions. However, the induction of PTI is complex. Our hypotheses are that (i) the recognition by the plant of PAMPs vs non-PAMP elicitors leads to specific defense profiles and (ii) the responses specifically induced by PAMPs target critical life history traits of the pathogen that produced them. We thus analyzed, using a metabolomic approach coupled with transcriptomic and hormonal analyses, the defense profiles induced in potato foliage treated with either a Concentrated Culture Filtrate (CCF) from Phytophthora infestans or two non-PAMP preparations, β-aminobutyric acid (BABA) and an Ulva spp. Extract, used separately. Each elicitor induced specific defense profiles. CCF up-regulated sesquiterpenes but down-regulated sterols and phenols, notably α-chaconine, caffeoyl quinic acid and rutin, which decreased spore production of P. infestans in vitro. CCF thus induces both defense and counter-defense responses. By contrast, the Ulva extract triggered the synthesis of a large-spectrum of antimicrobial compounds through the phenylpropanoid/flavonoid pathways, while BABA targeted the primary metabolism. Hence, PTI can be regarded as a heterogeneous set of general and pathogen-specific responses triggered by the molecular signatures of each elicitor, rather than as a uniform, non-specific and broad-spectrum set of general defense reactions.
Highlights
Plants have developed a complex immune system to protect themselves against pathogens and other biotic or abiotic stresses
Among these molecules are pathogen/microbe-associated molecular patterns (PAMPs/ MAMPs)—i.e. molecules produced by the pathogens or microorganisms and key to its survival and fitness [2], and other exogenous defense elicitors not related to pathogenicity
After filtering with analysis of variance (ANOVA) ( 0.05) tests, fold changes ( 2) and q-values (< 0.05) tests, up to 6969 features (1314 from electrospray ion source (ESI)- mode and a further 5655 from ESI+ mode in trial 1; 137 from ESI- mode and 4664 from ESI+ mode in trial 2) were detected in the UPLC-qTOF-MSe analysis of metabolites retrieved from Desiree leaf samples after elicitation with Concentrated Culture Filtrate (CCF), BABA or Ulva extract
Summary
Plants have developed a complex immune system to protect themselves against pathogens and other biotic or abiotic stresses. The first level in this immune system is based on the recognition by the plant of exogenous molecules or molecular patterns, which the plant uses as signatures of local disturbances of its environment. Among these molecules are pathogen/microbe-associated molecular patterns (PAMPs/ MAMPs)—i.e. molecules produced by the pathogens or microorganisms and key to its survival and fitness [2], and other exogenous defense elicitors not related to pathogenicity. Over the course of evolution, hosts have sometimes developed the ability to recognize specific avirulence factors This recognition triggers a second level of the immune system, effector-triggered immunity (ETI), which leads to the induction of more intense defense responses than PTI. ETI is generally considered to drive qualitative, gene-forgene resistance [5], which is generally less durable than the quantitative forms of resistance associated with PTI [6]
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