Schellenberger, R. | bioRxiv Science

bioRxiv2025

Pantoea ananatis-triggered systemic resistance requires root sensing through the LORE receptor kinase in Arabidopsis

Systemic immunity induced by beneficial bacteria helps plants to cope with subsequent pathogen attacks. However, how these bacteria are sensed by plants and how this sensing results in a systemic response is not well understood. Recently, the Brassicaceae LIPOOLIGOSACCHARIDE-SPECIFIC REDUCED ELICITATION (LORE) receptor kinase was identified as the direct sensor of bacterial medium-chain-length 3-hydroxy fatty acids (mc-3-OH-FAs) and 3-(3-hydroxyalkanoyloxy)alkanoic acids (HAAs), which activate systemic Brassicaceae immunity. Here, we show that the bacterium Pantoea ananatis BRT175, which produces HAAs, can colonize Arabidopsis thaliana roots independently of the production of these compounds. P. ananatis triggers induced systemic resistance (ISR) to the necrotrophic pathogen Botrytis cinerea, but not to the hemibiotrophic pathogen Pseudomonas syringae pv. tomato. Importantly, this ISR can be mimicked by HAAs or 3-hydroxy-decanoic acid (3-OH-C10). Both P. ananatis-triggered and 3-OH-C10-triggered ISR against B. cinerea are mediated by LORE sensing, involve salicylic acid, jasmonic acid and ethylene signaling pathways, and activate the expression of similar defense genes in infected leaves. Thus, 3-OH-C10 and HAAs are perceived by a pattern recognition receptor (PRR) in the root and activate a local immune response in roots as well as systemic immunity in leaves. Our study demonstrates that these lipidic microbe-associated molecular patterns (MAMPs), produced by beneficial microorganisms, are necessary and sufficient to trigger rhizobacteria-driven ISR. It further highlights the role of these MAMPs in differentially activating systemic resistance against biotrophic and necrotrophic pathogens.

plant biology↗

bioRxiv2020

Rhamnolipids and their 3-(3-hydroxyalkanoyloxy)alkanoic acid precursors activate Arabidopsis innate immunity through two independent mechanisms

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 mostly 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) that 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, albeit abolishing sensing by LORE, do not impair their ability to trigger plant defense. In addition, our results show that RL-triggered immune response 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. SignificanceActivation of plant innate immunity relies on the perception of microorganisms through self and nonself elicitors. Rhamnolipids and their precursor HAAs are exoproducts produced by beneficial and pathogenic bacteria. They are involved in bacterial surface dissemination and biofilm development. As these compounds are released in the extracellular milieu, they have the potential to be perceived by the plant immune system. Our work shows that both compounds independently activate plant immunity. We demonstrate that HAAs are perceived by the receptor protein kinase LORE. By contrast, rhamnolipids are not senses by LORE but activate a non-canonical immune response affected by the sphingolipid composition of the plant plasma membrane. Thus, plants are able to sense bacterial molecules as well as their direct precursors to trigger a distinct immune response.

plant biology↗