iTRAQ proteomics reveals the regulatory response to Xanthomonas campestris pv.vesicatoria in resistant vs.susceptible pepper genotypes

Bacterial spot(BS)is a severe bacterial disease induced by Xanthomonas campestris pv.vesicatoria(Xcv),a pathogen that causes serious damage to pepper growth and yield.It is therefore important to study the mechanisms of pepper resistance to Xcv and to breed and promote Xcvresistant pepper varieties.However,studies of the responses to Xcv infection in peppers at the protein level are limited.Here,we examined Xcv-induced proteomic changes in leaves of the BS susceptible bell pepper ECW and the resistant bell pepper VI037601 using the isobaric tags for relative and absolute quantitation(iTRAQ)-based protein labeling technology.A total of 6,120 distinct proteins were identified,and there were 1,289 significantly differentially accumulated proteins(DAPs)in ECW and VI037601 leaves after Xcv inoculation.Among these,339(250up-and 89 down-regulated)and 479(300 up-and 179 down-regulated)DAPs were specifically identified in ECW and VI037601,respectively,with 459(364 up-and 95 down-regulated)similarly expressed DAPs being shared by ECW and VI037601.Based on bioinformatics analysis,many defense-associated proteins were identified as up-regulated in ECW and VI037601,especially the proteins involved in plant-pathogen interaction,phenylpropanoid biosynthesis,protein processing in the endoplasmic reticulum,and MAPK signaling pathway-plant.Moreover,we evaluated transcript levels of six differentially expressed genes from the iTRAQ results by q RT-PCR.The analysis revealed transcriptional changes that were consistent with the changes at the protein level.This study will provide a valuable resource for understanding the molecular basis of pepper resistance to Xcv infection and for improving the disease resistance of pepper cultivars.

Characterization of Chinese Isolates of Mango Bacterial Canker Xanthomonas campestris pv. mangiferaeindicae

Mango bacterial canker is caused by Xanthomonas campestris pv. mangiferaeindicae. During 2009 and 2013,leaves,twigs and fruits of mango were collected from commercial and experimental mango fields with typical canker symptoms in Hainan,Guangxi,Guangdong and Szechwan Provinces of China. The causal agent was identified as X. campestris pv. mangiferaeindicae through KC semi-selective medium isolation,pathogenicity tests,and sequencing of the gyrB gene.

Genetic and Proteomic Analyses of a Xanthomonas campestris pv.campestris purC Mutant Deficient in Purine Biosynthesis and Virulence

Bacterial proliferation in hosts requires activation of a number of housekeeping pathways, including purine de novo biosynthesis. Although inactivation of purine biosynthesis genes can attenuate virulence, it is unclear which biochemical or virulence factors are associated with the purine biosynthesis pathway in vivo. We report that inactivation of purC, a gene encoding phosphoribosylaminoimidazole-succinocarboxamide synthase, caused complete loss of virulence in Xanthomonas campestris pv. cam- pestris, the causal agent of black rot disease of cruciferous plants. The purC mutant was a purine auxotroph; it could not grow on minimal medium, whereas addition of purine derivatives, such as hypoxanthine or adenine plus guanine, restored growth of the mutant. The purC mutation also significantly enhanced the production of an unknown purine synthesis associated pigment and extracellular polysaccharides by the bacterium. In addition, comparative proteomic analyses of bacteria grown on rich and minimal media revealed that the purC mutation affected the expression levels of diverse proteins involved in purine and pyrimidine synthesis, carbon and energy metabolisms, iron uptake, proteolysis, protein secretion, and signal transduction. These results provided clues to understanding the contributions of purine synthesis to bacterial virulence and interactions with host immune systems.

New insights on molecular regulation of biofilm formation in plant-associated bacteria

Biofilms are complex bacterial assemblages with a defined three-dimensional architecture, attached to solid surfaces, and surrounded by a self-produced matrix generally composed of exopolysaccharides, proteins, lipids and extracellular DNA. Biofilm formation has evolved as an adaptive strategy of bacteria to cope with harsh environmental conditions as well as to establish antagonistic or beneficial interactions with their host. Plant-associated bacteria attach and form biofilms on different tissues including leaves, stems,vasculature, seeds and roots. In this review, we examine the formation of biofilms from the plant-associated bacterial perspective and detail the recently-described mechanisms of genetic regulation used by these organisms to orchestrate biofilm formation on plant surfaces. In addition, we describe plant host signals that bacterial pathogens recognize to activate the transition from a planktonic lifestyle to multicellular behavior.