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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 plasmamembrane. In conclusion, RLs and their precursors released by bacteria can both be perceived by plants but through distinct mechanisms. [ABSTRACT FROM AUTHOR]

In this work, the capacity of the soil-applied herbicide flumioxazin (fmx) to trigger defence mechanisms was assessed using 6-week-old in vitro grown Vitis vinifera L. plantlets. Time-course studies demonstrated that the herbicide induced the expression of basic β-1,3-glucanase (Vvglu), basic chitinase (Vvchit1b) and PR10 (VvPR10.3) genes encoding three pathogenesis-related (PR) proteins involved in grapevine defence against pathogens. Thus, all transcripts accumulated in grapevine tissues to reach maximum values after 24–72 h of herbicide exposure, except for VvPR10.3 gene expression, which was induced in roots and stems but not in leaves. Induction of PR genes was observed to a greater extent in roots and leaves, and its intensity diminished in the stems although still remained noteworthy. The activities of β-1,3-glucanase and chitinase enzymes significantly increased in the whole plant after herbicide exposure and were still stimulated 21 days after the beginning of treatments. Similarly, the most remarkable effect occurred in roots. However, all enzyme activities tested were stimulated in the upper aerial tissues as well, indicating that fmx or a derived product acts systemically, likely via root uptake. [ABSTRACT FROM AUTHOR]