Scanning Electron Microscopy of Pierce's Disease Bacterium in Petiolar Xylem of Grape Leaves

Tyson, Greta E.

doi:10.1094/phyto-75-264

Cited by 50 publications

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“…Biofilm formation by E. amylovora is required for effective colonization of host xylem tissues, the exit of pathogen cells from infected leaves into host stems, and systemic spread within trees (6, 7). The impact of biofilm formation on xylem colonization has also been noted for several other plant pathogens, including Clavibacter michiganensis, Pantoea stewartii, and Xylella fastidiosa (12)(13)(14), and the ability to form biofilms appears to be a common strategy for the survival or transmission of phytopathogens (6, 15).The second messenger cyclic di-GMP (c-di-GMP) regulates biofilm formation in the majority of bacteria. In general, a high level of intracellular c-di-GMP positively regulates biofilm formation and negatively regulates swimming motility (16)(17)(18)(19).…”

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confidence: 96%

Cyclic Di-GMP Modulates the Disease Progression of Erwinia amylovora

et al. 2013

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The second messenger cyclic di-GMP (c-di-GMP) is a nearly ubiquitous intracellular signal molecule known to regulate various cellular processes, including biofilm formation, motility, and virulence. The intracellular concentration of c-di-GMP is inversely governed by diguanylate cyclase (DGC) enzymes and phosphodiesterase (PDE) enzymes, which synthesize and degrade c-di-GMP, respectively. The role of c-di-GMP in the plant pathogen and causal agent of fire blight disease Erwinia amylovora has not been studied previously. Here we demonstrate that three of the five predicted DGC genes in E. amylovora (edc genes, for Erwinia diguanylate cyclase), edcA, edcC, and edcE, are active diguanylate cyclases. We show that c-di-GMP positively regulates the secretion of the main exopolysaccharide in E. amylovora, amylovoran, leading to increased biofilm formation, and negatively regulates flagellar swimming motility. Although amylovoran secretion and biofilm formation are important for the colonization of plant xylem tissues and the development of systemic infections, deletion of the two biofilm-promoting DGCs increased tissue necrosis in an immature-pear infection assay and an apple shoot infection model, suggesting that c-di-GMP negatively regulates virulence. In addition, c-di-GMP inhibited the expression of hrpA, a gene encoding the major structural component of the type III secretion pilus. Our results are the first to describe a role for c-di-GMP in E. amylovora and suggest that downregulation of motility and type III secretion by c-di-GMP during infection plays a key role in the coordination of pathogenesis. Erwinia amylovora is the causal agent of fire blight and a devastating phytopathogen that infects plant species of the family Rosaceae, most notably apple and pear trees (1). E. amylovora can infect flowers, fruits, actively growing shoots, and rootstock crowns (2). During the primary infection via the flower (1), E. amylovora cells multiply rapidly on the stigma. Motility and free moisture are important factors in the subsequent dissemination of cells down the outside of the stigma to nectarthodes, which provide entry into the plant (3-5).Following flower infection, E. amylovora cells spread systemically through host vascular tissues and cortical parenchyma. The wilting symptoms of fire blight are the result of bacterial invasion, the secretion of extracellular polysaccharide (EPS), and the formation of biofilms within host xylem that plug these tubes, restricting water flow (6, 7). E. amylovora secretes two distinct EPSs, amylovoran and levan, both of which contribute to plant infection (6). Amylovoran is an acidic polysaccharide composed of repeating units of galactose and glucuronic acid (8-10), while levan is a homopolymer of fructose residues synthesized from sucrose by the secreted enzyme levansucrase (11). Biofilm formation by E. amylovora is required for effective colonization of host xylem tissues, the exit of pathogen cells from infected leaves into host stems, and systemic spread within trees (6, 7). The...

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confidence: 96%

Cyclic Di-GMP Modulates the Disease Progression of Erwinia amylovora

et al. 2013

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“…Vessels can become occluded by dense colonization, and high frequencies of blocked vessels are associated with disease symptom development (1)(2)(3). X. fastidiosa is responsible for diseases that cause economic loss in many agricultural plants; however, it can also live in symptomless hosts that serve as a source of inoculum (4).…”

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confidence: 99%

Cell-cell signaling controlsXylella fastidiosainteractions with both insects and plants

Newman

Almeida

Purcell

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

262

296

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Xylella fastidiosa, which causes Pierce's disease of grapevine and other important plant diseases, is a xylem-limited bacterium that depends on insect vectors for transmission. Although many studies have addressed disease symptom development and transmission of the pathogen by vectors, little is known about the bacterial mechanisms driving these processes. Recently available X. fastidiosa genomic sequences and molecular tools have provided new routes for investigation. Here, we show that a diffusible signal molecule is required for biofilm formation in the vector and for vector transmission to plants. We constructed strains of X. fastidiosa mutated in the rpfF gene and determined that they are unable to produce the signal activity. In addition, rpfF mutants are more virulent than the wild type when mechanically inoculated into plants. This signal therefore directs interaction of X. fastidiosa with both its insect vector and plant host. Interestingly, rpfF mutants can still form in planta biofilms, which differ architecturally from biofilms in insects, suggesting that biofilm architecture, rather than a passive response to the environment, is actively determined by X. fastidiosa gene expression. This article reports a cell-cell signaling requirement for vector transmission. Identification of the genes regulated by rpfF should elucidate bacterial factors involved in transmission and biofilm formation in the insect.

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“…Vessels are interconnected by channels, called bordered pits, that allow the passage of xylem sap but block the passage of larger objects due to the presence of a pit membrane (34). Bacterial cells attach to the vessel wall and multiply, forming biofilm-like colonies that can, when sufficiently large, completely occlude xylem vessels, blocking water transport (35). Many agriculturally important plants, such as citrus, almond, coffee, and grapevines, are susceptible to diseases caused by X. fastidiosa (20).…”

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confidence: 99%

“…Understanding the pattern of X. fastidiosa colonization of the xylem and relating this pattern to symptom expression will further our progress in understanding PD as well as the endophytic life-style of the pathogen. To this end, several other studies have analyzed X. fastidiosa in planta using various types of microscopy, including light microscopy (13,19), scanning electron microscopy (35), transmission electron microscopy (24), and immunofluorescence microscopy (4). In these studies, it was determined that the frequency of vessels colonized and blocked by X. fastidiosa in grapes is positively correlated with disease symptom development over the growing season (19) and within individual plants (35).…”

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confidence: 99%

Use of a Green Fluorescent Strain for Analysis ofXylella fastidiosaColonization ofVitis vinifera

Newman

Almeida

Purcell

et al. 2003

Appl Environ Microbiol

228

214

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Xylella fastidiosa causes Pierce's disease of grapevine as well as several other major agricultural diseases but is a benign endophyte in most host plants. X. fastidiosa colonizes the xylem vessels of host plants and is transmitted by xylem sap-feeding insect vectors. To understand better the pattern of host colonization and its relationship to disease, we engineered X. fastidiosa to express a green fluorescent protein (Gfp) constitutively and performed confocal laser-scanning microscopic analysis of colonization in a susceptible host, Vitis vinifera. In symptomatic leaves, the fraction of vessels colonized by X. fastidiosa was fivefold higher than in nearby asymptomatic leaves. The fraction of vessels completely blocked by X. fastidiosa colonies increased 40-fold in symptomatic leaves and was the feature of colonization most dramatically linked to symptoms. Therefore, the extent of vessel blockage by bacterial colonization is highly likely to be a crucial variable in symptom expression. Intriguingly, a high proportion (>80%) of colonized vessels were not blocked in infected leaves and instead had small colonies or solitary cells, suggesting that vessel blockage is not a colonization strategy employed by the pathogen but, rather, a by-product of endophytic colonization. We present evidence for X. fastidiosa movement through bordered pits to neighboring vessels and propose that vessel-to-vessel movement is a key colonization strategy whose failure results in vessel plugging and disease.

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Scanning Electron Microscopy of Pierce's Disease Bacterium in Petiolar Xylem of Grape Leaves

Cited by 50 publications

References 0 publications

Cyclic Di-GMP Modulates the Disease Progression of Erwinia amylovora

Cyclic Di-GMP Modulates the Disease Progression of Erwinia amylovora

Cell-cell signaling controlsXylella fastidiosainteractions with both insects and plants

Use of a Green Fluorescent Strain for Analysis ofXylella fastidiosaColonization ofVitis vinifera

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