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Plant innate immunity is activated upon perception of invasion pattern molecules by plant cell-surface immune receptors. Several bacteria of the genera Pseudomonas and Burkholderia produce rhamnolipids (RLs) from l-rhamnose and ( R )-3-hydroxyalkanoate precursors (HAAs). RL and HAA secretion is required to modulate bacterial surface motility, biofilm development, and thus successful colonization of hosts. Here, we show that the lipidic secretome from the opportunistic pathogen Pseudomonas aeruginosa , mainly comprising RLs and HAAs, stimulates Arabidopsis immunity. We demonstrate that HAAs are sensed by the bulb-type lectin receptor kinase LIPOOLIGOSACCHARIDE-SPECIFIC REDUCED ELICITATION/S-DOMAIN-1-29 (LORE/SD1-29), which also mediates medium-chain 3-hydroxy fatty acid (mc-3-OH-FA) perception, in the plant Arabidopsis thaliana HAA sensing induces canonical immune signaling and local resistance to plant pathogenic Pseudomonas infection. By contrast, RLs trigger an atypical immune response and resistance to Pseudomonas infection independent of LORE. Thus, the glycosyl moieties of RLs, although abolishing sensing by LORE, do not impair their ability to trigger plant defense. Moreover, our results show that the immune response triggered by RLs is affected by the sphingolipid composition of the plasma membrane. In conclusion, RLs and their precursors released by bacteria can both be perceived by plants but through distinct mechanisms., Competing Interests: Competing interest statement: Technical University of Munich has filed a patent application to inventors A.K., C.D., T.H., and S.R.

Plants are able to effectively cope with invading pathogens by activating an immune response based on the detection of invasion patterns (IPs) originating from the pathogen or released by the plant after infection. At a first level, this perception takes place at the plasma membrane through cell surface immune receptors and although the involvement of proteinaceous pattern recognition receptors (PRRs) is well established, increasing data are also pointing out the role of membrane lipids in the sensing of IPs. In this review, we discuss the evolution of various conceptual models describing plant immunity and present an overview of well-characterized IPs from different natures and origins. We summarize the current knowledge on how they are perceived by plants at the plasma membrane, highlighting the increasingly apparent diversity of sentinel-related systems in plants., (© 2019 The Authors. Molecular Plant Pathology published by British Society for Plant Pathology and John Wiley & Sons Ltd.)

Stimulation of plant innate immunity by natural and synthetic elicitors is a promising alternative to conventional pesticides for a more sustainable agriculture. Sugar-based bolaamphiphiles are known for their biocompatibility, biodegradability and low toxicity. In this work, we show that Synthetic Rhamnolipid Bolaforms (SRBs) that have been synthesized by green chemistry trigger Arabidopsis innate immunity. Using structure-function analysis, we demonstrate that SRBs, depending on the acyl chain length, differentially activate early and late immunity-related plant defense responses and provide local increase in resistance to plant pathogenic bacteria. Our biophysical data suggest that SRBs can interact with plant biomimetic plasma membrane and open the possibility of a lipid driven process for plant-triggered immunity by SRBs.

Although induced systemic resistance (ISR) is well-documented in the context of plant-beneficial bacteria interactions, knowledge about the local and systemic molecular and biochemical defense responses before or upon pathogen infection in grapevine is very scarce. In this study, we first investigated the capacity of grapevine plants to express immune responses at both above- and below-ground levels upon interaction with a beneficial bacterium, Pseudomonas fluorescens PTA-CT2. We then explored whether the extent of priming state could contribute to the PTA-CT2-induced ISR in Botrytis cinerea-infected leaves. Our data provide evidence that this bacterium colonized grapevine roots but not the above-ground plant parts and altered the plant phenotype that displayed multiple defense responses both locally and systemically. The grapevine roots and leaves exhibited distinct patterns of defense-related gene expression during root colonization by PTA-CT2. Roots responded faster than leaves and some responses were more strongly upregulated in roots than in leaves and vice versa for other genes. These responses appear to be associated with some induction of cell death in roots and a transient expression of HSR, a hypersensitive response-related gene in both local (roots) and systemic (leaves) tissues. However, stilbenic phytoalexin patterns followed opposite trends in roots compared with leaves but no phytoalexin was exuded during plant-bacterium interaction, suggesting that roots could play an important role in the transfer of metabolites contributing to immune response at the systemic level. Unexpectedly, in B. cinerea-infected leaves PTA-CT2-mediated ISR was accompanied in large part by a downregulation of different defense-related genes, including HSR. Only phytoalexins and glutathion-S-transferase 1 transcripts were upregulated, while the expression of anthocyanin biosynthetic genes was maintained at a higher level than the control. This suggests that decreased expression of HSR, as a marker of cell death, and activation of secondary metabolism pathways could be responsible for a reduced B. cinerea colonization capacity in bacterized plants.

Environmental factors including drought stress may modulate plant immune responses and resistance to pathogens. However, the relationship between mechanisms of drought tolerance and resistance to pathogens remained unknown. In this study, the effects of drought stress on polyamine (PA) homeostasis and immune responses were investigated in two grapevine genotypes differing in their drought tolerance; Chardonnay (CHR), as sensitive and Meski (MSK), as tolerant. Under drought conditions, MSK plants showed the lowest leaf water loss and reduction of photosynthetic efficiency, and expressed a lower level of NCED2, a gene involved in abscisic acid biosynthesis, compared with CHR plants. The improved drought tolerance in MSK was also coincident with the highest change in free PAs and up-regulation of the genes encoding arginine decarboxylase (ADC), copper amine-oxidase (CuAO), and PA-oxidases (PAO) and their corresponding enzyme activities. MSK plants also accumulated the highest level of amino acids, including Arg, Glu, Gln, Pro, and GABA, emphasizing the participation of PA-related amino acid homeostasis in drought tolerance. Importantly, drought-tolerant plants also exhibited enhanced phytoalexin accumulation and up-regulation of PR genes, especially PR-2 and Chit4c, compared with the sensitive plants. This is consistent with a lower susceptibility of MSK than CHR to Botrytis cinerea. Data suggest a possible connection between water stress tolerance and immune response in grapevine. Pharmacological experiments revealed that under drought conditions CuAO and PAO pathways were involved in the regulation of photosynthetic efficiency, and also of immune response and resistance of grapevine to a subsequent pathogen attack. These results open new views to improve our understanding of crosstalk between drought tolerance mechanisms and immune response., (© The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Plants harbor various beneficial microbes that modulate their innate immunity, resulting in induced systemic resistance (ISR) against a broad range of pathogens. Camalexin is an integral part of Arabidopsis innate immunity, but the contribution of its biosynthesis in ISR is poorly investigated. We focused on camalexin accumulation primed by two beneficial bacteria, Pseudomonas fluorescens and Bacillus subtilis , and its role in ISR against Botrytis cinerea and Pseudomonas syringae Pst DC3000. Our data show that colonization of Arabidopsis thaliana roots by beneficial bacteria triggers ISR against both pathogens and primes plants for enhanced accumulation of camalexin and CYP71A12 transcript in leaf tissues. Pseudomonas fluorescens induced the most efficient ISR response against B. cinerea , while B. subtilis was more efficient against Pst DC3000. Analysis of cyp71a12 and pad3 mutants revealed that loss of camalexin synthesis affected ISR mediated by both bacteria against B. cinerea. CYP71A12 and PAD3 contributed significantly to the pathogen-triggered accumulation of camalexin, but PAD3 does not seem to contribute to ISR against Pst DC3000. This indicated a significant contribution of camalexin in ISR against B. cinerea , but not always against Pst DC3000. Experiments with Arabidopsis mutants compromised in different hormonal signaling pathways highlighted that B. subtilis stimulates similar signaling pathways upon infection with both pathogens, since salicylic acid (SA), but not jasmonic acid (JA) or ethylene, is required for ISR camalexin accumulation. However, P. fluorescens -induced ISR differs depending on the pathogen; both SA and JA are required for camalexin accumulation upon B. cinerea infection, while camalexin is not necessary for priming against Pst DC3000. [ABSTRACT FROM AUTHOR]

Rhamnolipids are known as very efficient biosurfactant molecules. They are used in a wide range of industrial applications including food, cosmetics, pharmaceutical formulations and bioremediation of pollutants. The present review provides an overview of the effect of rhamnolipids in animal and plant defense responses. We describe the current knowledge on the stimulation of plant and animal immunity by these molecules, as well as on their direct antimicrobial properties. Given their ecological acceptance owing to their low toxicity and biodegradability, rhamnolipids have the potential to be useful molecules in medicine and to be part of alternative strategies in order to reduce or replace pesticides in agriculture. [ABSTRACT FROM AUTHOR]