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Plant structural and storage glucans trigger distinct transcriptional responses that modulate the motility of Xanthomonas pathogens

ABSTRACT: Some phytopathogens are outfitted with a broad and diverse repertoire of enzymatic systems that enable the breakdown and utilization of host polysaccharides as a source of carbon, energy, and stimuli. However, the functional assignment of these enzymatic systems and the influence of their products on modulating pathogen behavior during host colonization is yet poorly comprehended. In this study, we performed RNA-seq analyses to provide a comprehensive, genome-wide view of the transcriptional response of the model phytopathogen Xanthomonas citri pv. citri 306 (hereafter X. citri 306) to cellobiose, a component of structural β-1,4-glucans (majorly cellulose), and storage α-glucans, seeking to better understand how they are assimilated and the impacts of their sensing on bacterial behavior and physiology. Structural β-1,4-glucans and storage α-glucans (starch) are spatially discretized in the plant cell, therefore representing spatiotemporal references for the bacterium during host colonization. Combining transcriptional and genome mining analyses with gene knockout and cell motility assays, we show that X. citri 306 harbors molecular systems for the breakdown and assimilation of these carbohydrates, revealing that cellobiose upregulates genes related to flagellum assembly and type IV pili, inducing a higher-motility state. In contrast, starch suppresses genes related to chemotaxis, flagellum assembly and biofilm dispersion, decreasing motility. Taken together, these results unravel that besides using structural β-glucans and storage α-glucans as sources of carbon and energy, Xanthomonas bacteria also sense them, adapting its metabolism and controlling transitions between higher and lower motility states for successful host colonization.

ORGANISM(S): Xanthomonas citri pv. citri

PROVIDER: GSE234477 | GEO | 2023/09/26

REPOSITORIES: GEO

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Project description:Xanthomonas is one important model microbe to study the molecular determinants of virulence and host range of pathogens since Xanthomonas is capable of infecting numerous monocotyledonous and dicotyledonous plants. Among the plant diseases caused by Xanthomonas, X. citri subsp. citri (Xcc) causes citrus canker, which has significant impact on citrus production. Xcc is classified into different strains primarily by host range including A and Aw. The A (Asiatic) strain (XccA) has a wide host range and is most virulent, whereas Aw (Wellington) strain has restricted host range including Key or Mexican lime and alemow. We hypothesized that not only gene content but also gene expression contributes to the difference in virulence and host range of closely related strains. To test our hypothesis, comparative genomic and transcriptome analyses were conducted to study the two closely related Xcc A and Aw strains. The genome of X. citri subsp. citri strain Aw12879 (Xcaw) was completely sequenced using 454 Pyrosequencing, Illumina sequencing and Optical mapping. The finished genome (5.3 Mb chromosome and two plasmids pXcaw19 and pXcaw58) of Xcaw was annotated, curated and compared with XccA genome. Protein blast revealed multiple genes including type III secretion system (TIIISS) effectors xopAF and xopAG are present in Xcaw but absent in XccA. Comparative genomic analysis showed various changes in genes encoding LPS and type IV secretion system. Furthermore, RNA-Seq was used to compare expression profile of Xcaw and XccA in nutrient rich (NB) medium and XVM2 medium which is known to mimic the intercellular space of plant cells using Illumina sequencing. Multiple avirulence/effector genes were over-expressed in Xcaw compared to XccA which might contribute to the limited host range of Xcaw compared to XccA. The overexpression of genes involved in cell wall degradation, attachment, ROS (reactive oxygen species) scavenging, nutrient transportation in XccA might contribute to its expanding of host range. Our data suggest that both gene content and gene expression contribute to difference in virulence and host range of bacterial pathogens. This study lays the foundation to further characterize the mechanisms for virulence and host range of strains of X. citri subsp. citri and other bacterial pathogens. mRNA expression profiles of Xcc strain A and Aw were generated in 2 media: NB and XVM2 by deep sequencing, in triplicate, using Illumina GAII.

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Plant structural and storage glucans trigger distinct transcriptional responses that modulate the motility of Xanthomonas pathogens

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