Recently, "mBio", an international authoritative journal in the field of microbiology, published online a research article by Professor He Yawen's team from the School of Life Science and Technology, Shanghai Jiaotong University, "The plant defense signal salicylic acid increases the intracellular and extracellular pH of the phytopathogenic Xanthomonas spp.
Activates RpfB-degrading enzyme activity and induces DSF quorum sensing signal turnover (The Plant Defense Signal Salicylic Acid Activates the RpfB-Dependent Quorum Sensing Signal Turnover via Altering the Culture and Cytoplasmic pH in the Phytopathogen Xanthomonas campestris)
” Song Kai, a doctoral student from the School of Life Science and Technology, is the first author of the article, and Professor He Yawen is the corresponding author.
Professor Chan Kok-Gan from University of Malaysia and Researcher Zhang Hongyan from Shanghai Nongle Biological Products Co.
participated in part of the research work of the article
Xanthomonas is a class of Gram-negative bacteria that can infect more than 400 kinds of plants, including many important crops and cash crops, causing serious economic losses
DSF signaling-dependent quorum-sensing mechanisms regulate the expression of Xanthomonas virulence factors during plant infection
Professor He Yawen's team has long studied the molecular mechanism of quorum sensing in the plant pathogen Xanthomonas, identified the chemical structure, signal transduction pathway and regulatory biological function of DSF signal molecules, and clarified the molecular mechanism of DSF biosynthesis and signal turnover
On this basis, Ph.
student Song Kai et al.
first found that during the infection of Xanthomonas (Xcc), the host plant would synthesize a large amount of salicylic acid (SA) in the adjacent area of the infection, resulting in the complete exposure of Xcc to Under the action of SA, Xcc cannot utilize and degrade SA
Using an XYS medium specially formulated to simulate the nutrient environment faced by Xcc during plant infection, it was found that exogenous addition of 50-100 mM SA to the Xcc XYS culture system or endogenous synthesis of SA in Xcc would significantly increase the Decreases DSF levels and induces DSF turnover
This phenomenon requires the participation of the DSF-degrading enzyme RpfB, but SA does not affect the transcription and translation levels of rpfB, nor does it affect the expression and translation of the DSF synthase gene rpfF
Schematic diagram of the molecular mechanism of salicylic acid-induced DSF quorum-sensing signal turnover.
(A) Xanthomonas campestris (Xcc) infects cabbage leaves, causing V-type lesions; (B) Xcc infection induces cabbage A large number of SA signaling molecules are produced; (C) The pathway pattern diagram of SA directly acting on Xcc to induce the turnover of DSF signaling molecules
Further research found that with the growth of Xanthomonas Xcc in XYS medium, the pH value of the culture system gradually decreased to an acidic environment (~4.
7), and the addition of exogenous SA or endogenous synthetic SA significantly increased the intracellular and intracellular levels of Xcc.
In the absence of SA, artificially increasing the pH of the Xcc XYS culture system from 6 to 8 also induced the inversion of DSF, and the participation of RpfB was necessary
On the other hand, if the pH of the XYS culture system was fixed at 7 by the buffer system, even the exogenous addition of SA could not induce DSF signal turnover
These results indicated that SA could induce the turnover of DSF by increasing the intracellular and extracellular pH of Xcc, increasing the enzymatic activity of RpfB
In order to test this hypothesis, the authors expressed and purified RpfB protein, established an enzymatic reaction system for the degradation of DSF by RpfB in vitro, and found that increasing the pH of the in vitro reaction system could increase the activity of RpfB to degrade DSF, but SA did not.
Direct interaction with RpfB affects its degradation activity
Finally, the pathogenicity of SA-treated Xcc strains on cabbage leaves was significantly different from that of untreated strains, further validating the function of SA
SA is an important plant defense hormone, and the current research focus is the signal transduction pathway and induced immune response of SA in plants
This study fully demonstrates that plant-generated SA signals can also act directly on invading pathogens, interfering with their quorum sensing systems and pathogenicity, enriching our understanding of the interactions between Xanthomonas and crucifers
This research was supported by the National Key R&D Program, the National Natural Science Foundation of China, and Shanghai Nongle Biological Products Co.
School of Life Science and Technology
School of Life Science and Technology