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.

植物先天免疫在植物细胞表面免疫受体感知到入侵模式分子后被激活。假单胞菌属和伯克霍尔德氏菌属的几种细菌从L-鼠李糖和 ( R )-3-羟基链烷酸酯前体 (HAAs) 产生鼠李糖脂 (RL)。 RL 和 HAA 的分泌对于调节细菌表面运动、生物膜发育以及宿主的成功定殖是必需的。在这里，我们证明来自机会性病原体铜绿假单胞菌的脂质分泌组（主要包含 RL 和 HAA）可刺激拟南芥免疫。我们证明 HAA 可以被球状凝集素受体激酶 LIPOOLIGOSACCHARIDE-SPECIFIC REDUCED ELICITATION/S-DOMAIN-1-29 (LORE/SD1-29) 感知，该激酶还介导中链 3-羟基脂肪酸 (mc-3) -OH-FA）感知，在拟南芥植物中。 HAA 感应可诱导经典免疫信号传导和对植物致病性假单胞菌感染的局部抵抗力。相比之下，RL 会触发非典型的免疫反应和对假单胞菌感染的抵抗力，与 LORE 无关。因此，RL 的糖基部分虽然消除了 LORE 的感应，但不会削弱它们触发植物防御的能力。此外，我们的结果表明，RL 引发的免疫反应受到质膜鞘脂成分的影响。总之，细菌释放的 RL 及其前体都可以被植物感知，但通过不同的机制。