Global Regulator PhoP is Necessary for Motility, Biofilm Formation, Exoenzyme Production, and Virulence of Xanthomonas citri Subsp. citri on Citrus Plants

Abstract

Citrus canker caused by Xanthomonas citri subsp. citri is one of the most important bacterial diseases of citrus, impacting both plant growth and fruit quality. Identifying and elucidating the roles of genes associated with pathogenesis has aided our understanding of the molecular basis of citrus-bacteria interactions. However, the complex virulence mechanisms of X. citri subsp. citri are still not well understood. In this study, we characterized the role of PhoP in X. citri subsp. citri using a phoP deletion mutant, ΔphoP. Compared with wild-type strain XHG3, ΔphoP showed reduced motility, biofilm formation, as well as decreased production of cellulase, amylase, and polygalacturonase. In addition, the virulence of ΔphoP on citrus leaves was significantly decreased. To further understand the virulence mechanisms of X. citri subsp. citri, high-throughput RNA sequencing technology (RNA-Seq) was used to compare the transcriptomes of the wild-type and mutant strains. Analysis revealed 1017 differentially-expressed genes (DEGs), of which 614 were up-regulated and 403 were down-regulated in ΔphoP. Gene ontology functional enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analyses suggested that the DEGs were enriched in flagellar assembly, two-component systems, histidine metabolism, bacterial chemotaxis, ABC transporters, and bacterial secretion systems. Our results showed that PhoP activates the expression of a large set of virulence genes, including 22 type III secretion system genes and 15 type III secretion system effector genes, as well as several genes involved in chemotaxis, and flagellar and histidine biosynthesis. Two-step reverse-transcription polymerase chain reaction analysis targeting 17 genes was used to validate the RNA-seq data, and confirmed that the expression of all 17 genes, except for that of virB1, decreased significantly. Our results suggest that PhoP interacts with a global signaling network to co-ordinate the expression of multiple virulence factors involved in modification and adaption to the host environment during infection.

Prevalence and Specificity of Chemoreceptor Profiles in Plant-Associated Bacteria

“…This list includes CRs that are upregulated in Dickeya dadantii 3937 and Pectobacterium carotovorum WPP14, two soft-rot bacterial strains ( 39 ); Dickeya dianthicola RNS04.9, which grows on macerated potato tubers ( 40 ); and Xanthomonas fragariae , which grows on strawberry leaves ( 41 ). Similarly, we found several CRs with very high DPS values (80%) that were shown to be relevant in Xanthomonas citri virulence ( 42 ) or required for fitness of Pseudomonas savastanoi pv. savastanoi in olive knots ( 43 ).…”

Complete genome analysis of a virulent Vibrio scophthalmi strain VSc190401 isolated from diseased marine fish half-smooth tongue sole, Cynoglossus semilaevis

“…NR database comparative analysis results showed that the coverage of coding protein sequences was 100%, and their identity was 88.4-100%. Other studies have confirmed that RelA and Phop gene regulate the synthesis of bacterial virulence factors as well as their primary and secondary metabolites, thus affecting the bacterial pathogenicity [28,29]. In addition, the virulence-related gene sequences of ompA (identity 90-100%), hemolysin (identity 96.7-100%), betahemolysin/cytolysin (identity 98.2-100%), enterobactin (identity 99.8-100%), and T2SS (identity 97.2-100%) were also found in the whole genome of the strain VSc190401.…”

Complete Genome Analysis of A Virulent Vibrio Scophthalmi Strain VSc190401 Isolated form Diseased Marine Fish Half-Smooth Tongue Sole, Cynoglossus Semilaevis

“…NR database comparative analysis results showed that the coverage of coding protein sequences was 100%, and their identity was 88.4%-100%. Other studies have confirmed that RelA and Phop gene regulate the synthesis of bacterial virulence factors as well as their primary and secondary metabolites, thus affecting the bacterial pathogenicity [33,34]. In addition, the virulence-related gene sequences of ompA (identity 90%-100%), hemolysin (identity 96.7%-100%), beta-hemolysin/cytolysin (identity 98.2%-100%), enterobactin (identity 99.8%-100%), and T2SS (identity 97.2%-100%) were also found in the whole genome of the strain VSc190401.…”