RESUMO
To better understand the behavior of Xanthomonas axonopodis pv. glycines, the causal agent of bacterial pustule of soybean within its host, its global transcriptome within soybean leaves was compared with that in a minimal medium in vitro, using deep sequencing of mRNA. Of 5,062 genes predicted from a draft genome of X. axonopodis pv. glycines, 534 were up-regulated in the plant, while 289 were down-regulated. Genes encoding YapH, a cell-surface adhesin, as well as several others encoding cell-surface proteins, were down-regulated in soybean. Many genes encoding the type III secretion system and effector proteins, cell wall-degrading enzymes and phosphate transporter proteins were strongly expressed at early stages of infection. Several genes encoding RND multidrug efflux pumps were induced in planta and by isoflavonoids in vitro and were required for full virulence of X. axonopodis pv. glycines, as well as resistance to soybean phytoalexins. Genes encoding consumption of malonate, a compound abundant in soybean, were induced in planta and by malonate in vitro. Disruption of the malonate decarboxylase operon blocked growth in minimal media with malonate as the sole carbon source but did not significantly alter growth in soybean, apparently because genes for sucrose and fructose uptake were also induced in planta. Many genes involved in phosphate metabolism and uptake were induced in planta. While disruption of genes encoding high-affinity phosphate transport did not alter growth in media varying in phosphate concentration, the mutants were severely attenuated for growth in soybean. This global transcriptional profiling has provided insight into both the intercellular environment of this soybean pathogen and traits used by X. axonopodis pv. glycines to promote disease.
Assuntos
Glycine max/microbiologia , Interações Hospedeiro-Patógeno/genética , Folhas de Planta/microbiologia , Xanthomonas axonopodis/genética , Xanthomonas axonopodis/patogenicidade , Regulação Bacteriana da Expressão Gênica , Malonatos/metabolismo , Fósforo/metabolismoRESUMO
A novel luxR homolog, termed XagR, in Xanthomonas axonopodis pv. glycines, the cause of soybean pustule, controls expression of pip, yapH, and at least 77 other genes. Although XagR and Pip are required for full virulence of X. axonopodis pv. glycines to soybean, constitutive overproduction of XagR suppresses infection. The xagR-dependent induction of pip occurs in planta only 2 days or more after inoculation. Although the transcription of xagR appears constitutive, XagR accumulates only in cells that have colonized soybean plants for more than 2 days suggesting that some components produced during the infection process mediate post-transcriptional control, likely by protecting XagR from proteolytic degradation. XagR modulates the adhesiveness of the pathogen during the infection process by suppressing the adhesin YapH. Although yapH mutants incite more infections of soybean leaves than the wild-type strain when topically applied under dry conditions, the mutant causes fewer infections when leaves are subject to simulated rain events after inoculation. Likewise, yapH mutants and cells in which XagR was overexpressed exhibited much more egress from infected leaves than the wild-type strain. Thus, XagR differentially modulates expression of a variety of genes during the infection process in response to feedback from plant molecules elaborated during infection to coordinate processes such as invasion, infection, and cell egress needed to complete the disease cycle.
Assuntos
Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Glycine max/microbiologia , Xanthomonas axonopodis/patogenicidade , Aderência Bacteriana/genética , Sequência de Bases , Regulação Bacteriana da Expressão Gênica , Genoma Bacteriano , Interações Hospedeiro-Patógeno/genética , Dados de Sequência Molecular , Mutação , Doenças das Plantas/microbiologia , Folhas de Planta/microbiologia , Regulon , Proteínas Repressoras/metabolismo , Transativadores/metabolismo , Virulência/genéticaRESUMO
Three races of Xanthomonas axonopodis pv. glycines were identified on pustule disease resistant and susceptible soybean cultivars based on virulence phenotype. For race 3, an avrBs3 homolog, avrXg1 was identified that conferred resistance expressed as a hypersensitive response on resistant cultivar Williams 82. Mutations in two predicted functional domains of avrXg1 resulted in gained virulence on Williams 82 and an increase in bacterial population number on susceptible cultivars. Expression of avrXg1 in race 1, that is predicted to confer a nonspecific HR, led to virulence on susceptible cultivars Spencer and PI 520733. Expression of avrXg1 in race 2, that is predicted of carrying avrBs3-like genes, resulted in gained virulence and fitness of pathogen on both resistant and susceptible cultivars. The results demonstrate multifunctions for avrXg1 dependent on pathogen and plant genetic backgrounds.
Assuntos
Proteínas de Bactérias/genética , Glycine max/microbiologia , Xanthomonas/patogenicidade , Sequência de Aminoácidos , Proteínas de Bactérias/metabolismo , Regulação Bacteriana da Expressão Gênica/fisiologia , Genoma Bacteriano , Dados de Sequência Molecular , Isoformas de Proteínas , Especificidade da Espécie , VirulênciaRESUMO
To compare overall genome structure and transcription activator-like effector content, we completely sequenced Xanthomonas axonopodis pv. glycines strain 12-2, isolated in 1992 in Thailand, and strain EB08, isolated in 2008 in the United States (Iowa) using PacBio technology. We reassembled the genome sequence for a second US strain, 8ra, derived from a 1980 Iowa isolate, from existing PacBio reads. Despite geographic and temporal separation, the three genomes are highly syntenous, and their transcription activator-like effector repertoires are highly conserved.