The EMBO Journal: Bacterial free fatty acids stimulate an immune response in plants.

On January 10, 2020, the EMBO journal published a research paper entitled "tyrosine phosphorylation of the lore lectin receptor like kinase analogues plant immunity" by Liu Jun, Institute of Microbiology, Chinese Academy of Sciences and center of excellence in biological interaction（ DOI:10.15252/embj.2019102856 ）The molecular mechanism of plant immune response stimulated by fatty acids carried by bacteria was reported.lipopolysaccharide (LPS) is a component of the extracellular membrane of Gram-negative bacteria.in clinic, LPS is the main substance to stimulate human immunity and cause heat shock.in 1998, Bruce Beutler of Southwest Medical Center of the United States discovered the mammalian LPS receptor (1) and won the 2011 Nobel Prize in physiology or medicine.although many studies have confirmed that LPS can stimulate immune response in plants, its receptor and signaling pathway of stimulating plant immunity have not been clear.ranf et al. Recently reported that lore, a receptor on plant cell membrane, can recognize free medium carbon chain length 3-hydroxyfatty acids which are tightly bound to LPS. Among them, 3-oh-c10:0 of 10 carbons can significantly activate lore mediated plant defense response (2,3).the 3-hydroxy fatty acids with medium carbon chain length are the components of LPS. They are like a unique marker of Gram-negative bacteria, and the receptor lore is like a sentinel. When lore finds these free markers, it will alarm the plant defense.the research team of Liu Jun found that the receptor lore can cause the phosphorylation of a tyrosine site of itself when it recognizes 3-oh-c10:0, which triggers the plant defense response system.in order to find out the downstream executors of lore signal, the team identified three receptor kinases pbl34, PbL35 and pbl36 involved in downstream signal transmission after lore activation by immunoprecipitation and mass spectrometry.lore also phosphorylates the specific sites of these three kinases to inform the invasion of bacteria.these phosphorylated kinases further activate downstream defense modes, such as building callose on the cell wall and promoting the production of killer reactive oxygen species, which are very effective against invasive pathogens such as Pseudomonas syringae.however, many pathogens have evolved proteins to break the defense lines established by plants.in this study, the researchers found that Pseudomonas syringae can secrete a phosphatase during infection, which directly targets lore and removes the phosphorylation of tyrosine site on lore receptor, thus inhibiting the lore mediated plant immune response.therefore, the discovery further explains the process of identification and evolution between bacteria and plants, that is, bacteria inevitably produce 3-hydroxyfatty acids in the process of LPS synthesis, but they can secrete a protein to interfere with the defense process of plants, thus making Pseudomonas syringae a pathogenic bacterium with extensive host.3-hydroxyfatty acids are undoubtedly becoming an important class of substances to stimulate plant defense response, but many questions remain to be answered, such as whether they will be recognized by different plants? In addition, is there a mechanism to remove the phosphatase function of the pathogen in plants? The revelation of these problems will further enrich our understanding of the mechanism of plant resistance to bacterial invasion.Fig. 1: molecular mechanism of plant recognition of fatty acids carried by pathogens and the response strategies of pathogens.plant receptor lore senses the intermediate chain length 3-hydroxyfatty acids carried by the pathogen, causing the phosphorylation of lore tyrosine Y600 site; the phosphorylated lore further transfers phosphorylated intracellular receptor like kinases, such as pbl34, and further activates the immune response. however, the bacteria can secrete the protein hopao1 to remove the phosphorylation of lorey600 and inhibit the immune response. original link: References: 1. Poltorak, A., he, X., smirnova, I., Liu, m.y., van huffel, C., Du, X., birdwell, D., Alejos, e., Silva, M., Galanos, C., et al. (1998). Defective LPS signaling in C3H / HEJ and C57BL / 10sccr mice:mutations in Tlr4 gene. Science 282,2085-2088.2. Ranf, S., Gisch, N., Schaffer, M., Illig, T., Westphal, L., Knirel,Y.A., Sanchez-Carballo, P.M., Zahringer, U., Huckelhoven, R., Lee, J., et al. (2015). A lectin S-domainreceptor kinase mediates lipopolysaccharide sensing in Arabidopsis thaliana. Nature immunology 16, 426-433.3. Kutschera, A.,Dawid, C., Gisch, N., Schmid, C., Raasch, L., Gerster, T., Schaffer, M.,Smakowska-Luzan, E., Belkhadir, Y., Vlot, A.C., et al. (2019). Bacterial medium-chain3-hydroxy fatty acid metabolites trigger immunity in Arabidopsis plants.Science 364, 178-181.