The Liu Jun Research Group of the Institute of Microbiology reveals a new mechanism for plants to identify pathogenic bacteria.

Pseudomonas is a very important bacterial disease. Pseudomonas aeruginosa in this genus can infect animals and people as opportunistic pathogens.Pseudomonas syringae is the top ten plant pathogenic bacteria, which can infect tomato and other crops and cause serious economic losses.on January 10, 2020, the famous journal the EMBO journal published the latest research results of Liu Jun's research group, the research paper entitled "tyrosine phosphorylation of the lectin receptor like kinase lot regulations plant immunity".this study revealed that immune receptors on plant cell membranes recognize the medium chain length 3-hydroxyfatty acids carried by pathogenic bacteria, which are important components of lipopolysaccharide (LPS) synthesis.lipopolysaccharide (LPS) is an important component of the outer 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 the mechanism of stimulating plant immune response are still unclear.ranf et al. Recently reported that lore, a lectin receptor like kinase on plant cell membrane, can recognize free 3-hydroxy fatty acids with medium carbon chain length during LPS synthesis, among which 3-oh-c10:0 of 10 carbons can significantly activate lore mediated plant defense response (2,3).the study of Liu Jun's research group showed that the lectin receptor kinase lore is a bispecific kinase with serine / threonine and tyrosine kinase activities.further, a key self phosphorylation site y600f was identified by in vitro phosphorylation and protein mass spectrometry. The mutation of this site reduced the self phosphorylation activity of lore (Fig. 1a).genetic complementation experiments showed that Y600 mutation made plants lose recognition of 3-oh-c10:0 produced by pathogenic bacteria (Fig. 1b).in order to further analyze the mechanism of lore initiating immune response, the interaction protein pbl34 of lore was identified by immunoprecipitation and mass spectrometry.pbl34 is a receptor like cytoplasmic kinase, and it has two homologous proteins PbL35 and pbl36.the triple mutant pbl34 / 35 / 36 showed a reduced sensitivity to 3-oh-c10:0 (Fig. 1c).in vitro biochemical tests showed that lore could directly phosphorylate pbl34 and activate it (Fig. 1D), and this phosphorylation was dependent on lore phosphorylation site Y600 (Fig. 1E).interestingly, the effector protein hopao1 secreted by Pseudomonas syringae can inhibit the ROS burst induced by 3-oh-c10:0 (Fig. 1F). biochemical tests in vitro and in vivo showed that hopao1, as a phosphatase, could directly remove phosphorylation of Y600, thus inhibiting the activation of lore and its activation of downstream PBLs (Fig. 2). these results reveal the molecular mechanism by which plants perceive the small molecule metabolite 3-hydroxyfatty acids (3-hydroxyfatty acids) derived from pathogenic bacteria through receptors on cell membrane, and initiate downstream immune response. this kind of medium chain fatty acids can be used as chemical substances to induce plant resistance, which has potential application prospects. Fig. 1. Phosphorylation of lore and downstream intracellular receptor like kinases mediate plant immune response. A.y600 mutation reduces lore kinase activity; B. Y600 mutation reduces plant sensitivity to 3-oh-c10:0; C. PBLs triple mutant is less sensitive to 3-oh-c10:0; D. lore phosphorylates pbl34 in vitro; e. lore partially depends on Y600 for pbl34 phosphorylation; F The effector protein hopao1 inhibits ROS burst in plants. Liu Jun's research group has long been committed to studying the molecular mechanism of plant resistance to pathogenic bacteria and fungi. based on Arabidopsis thaliana and Pseudomonas syringae, rice and Magnaporthe grisea, it was found that lectin receptor kinases can activate the ROS salicylic acid pathway through calcium dependent protein kinases, thus enabling plants to acquire systemic resistance (Xu et al., MPMI, 2017; Luo et al., plant physiology, 2017). in the study of interaction between rice and Magnaporthe grisea, the proteins on rice cell membrane responding to Magnaporthe grisea infection were systematically identified by cell membrane proteomics for the first time (Cao et al., MPMI, 2016). at the same time, we also found that ethylene signaling pathway is regulating the mechanism of rice resistance to Magnaporthe grisea (Yang et al., Plant Journal, 2017), and revealed the mechanism of rice extracellular immunity stimulated by Magnaporthe grisea (Yang et al., the plant cell, 2018). Br / > further response mechanism of Phospho acid receptor in plant to phospho acid tyrosine kinase (lore) in response to the phospho acid receptor (lore) in plants. however, the bacteria can secrete the protein hopao1 to remove the phosphorylation of lorey600 and inhibit the immune response. the doctoral students Luo Xuming and Liang Yingbo of Liu Jun's research group and Wu Wei, doctoral students of Fujian agriculture and Forestry University, are the co first authors of the paper, and researcher Liu Jun is the corresponding author of the paper. the project has been supported by the national key R & D program, the Chinese Academy of Sciences pilot project (category B), the "Hundred Talents Program" start-up funding, and the National Natural Science Foundation of China. References: 1. Poltorak, a, et al (1998). Defective LPS signaling in C3H / HEJ and C57BL / 10sccr: mutations in tlr4gene. Science 282: 2085-2088.2. 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