Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Xylella”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources
PubMed2003

Comparative analyses of the complete genome sequences of Pierce's disease and citrus variegated chlorosis strains of Xylella fastidiosa.

Xylella fastidiosa is a xylem-dwelling, insect-transmitted, gamma-proteobacterium that causes diseases in many plants, including grapevine, citrus, periwinkle, almond, oleander, and coffee. X. fastidiosa has an unusually broad host range, has an extensive geographical distribution throughout the American continent, and induces diverse disease phenotypes. Previous molecular analyses indicated three distinct groups of X. fastidiosa isolates that were expected to be genetically divergent. Here we report the genome sequence of X. fastidiosa (Temecula strain), isolated from a naturally infected grapevine with Pierce's disease (PD) in a wine-grape-growing region of California. Comparative analyses with a previously sequenced X. fastidiosa strain responsible for citrus variegated chlorosis (CVC) revealed that 98% of the PD X. fastidiosa Temecula genes are shared with the CVC X. fastidiosa strain 9a5c genes. Furthermore, the average amino acid identity of the open reading frames in the strains is 95.7%. Genomic differences are limited to phage-associated chromosomal rearrangements and deletions that also account for the strain-specific genes present in each genome. Genomic islands, one in each genome, were identified, and their presence in other X. fastidiosa strains was analyzed. We conclude that these two organisms have identical metabolic functions and are likely to use a common set of genes in plant colonization and pathogenesis, permitting convergence of functional genomic strategies.

Base Sequence↗
PubMed2002

Whole-genome analysis of transporters in the plant pathogen Xylella fastidiosa.

The transport systems of the first completely sequenced genome of a plant parasite, Xylella fastidiosa, were analyzed. In all, 209 proteins were classified here as constitutive members of transport families; thus, we have identified 69 new transporters in addition to the 140 previously annotated. The analysis lead to several hints on potential ways of controlling the disease it causes on citrus trees. An ADP:ATP translocator, previously found in intracellular parasites only, was found in X. fastidiosa. A P-type ATPase is missing-among the 24 completely sequenced eubacteria to date, only three (including X. fastidiosa) do not have a P-type ATPase, and they are all parasites transmitted by insect vectors. An incomplete phosphotransferase system (PTS) was found, without the permease subunits-we conjecture either that they are among the hypothetical proteins or that the PTS plays a solely metabolic regulatory role. We propose that the Ttg2 ABC system might be an import system eventually involved in glutamate import rather than a toluene exporter, as previously annotated. X. fastidiosa exhibits fewer proteins with > or =4 alpha-helical transmembrane spanners than any other completely sequenced prokaryote to date. X. fastidiosa has only 2.7% of all open reading frames identifiable as major transporters, which puts it as the eubacterium having the lowest percentage of open reading frames involved in transport, closer to two archaea, Methanococcus jannaschii (2.4%) and Methanobacterium thermoautotrophicum (2.4%).

Bacterial Outer Membrane Proteins↗
PubMed2000

Nutritional requirements of Xylella fastidiosa, which causes Pierce's disease in grapes.

A defined medium (XF-26) containing 3 inorganic salts, 2 tricarboxylic acids, 17 amino acids, potato starch, phenol red, and agar was used as the starting point for the study. Deletions of one or more ingredients were performed to prepare various media. A medium was considered able to support growth of Xylella fastidiosa strains responsible for Pierce's disease in grapes, only after 10 serial passages had been completed. Of 3 inorganic salts, K2HPO4 and MgSO4 x 7H2O were essential, and (NH4)2HPO4 was nonessential for growth. Of the Krebs cycle intermediates, all (citrate, alpha-ketoglutarate, succinate, fumarate, malate, and oxaloacetate) but isocitrate supported growth of cultivated strains, whereas only citrate alone or citrate plus succinate supported the primary isolation of PD bacterium. Of 17 amino acids, 6 uncharged polar R groups (asparagine, cysteine, glutamine, glycine, serine, and threonine) supported growth, whereas 8 nonpolar R groups (alanine, isoleucine, leucine, methionine, phenylalanine, proline, tryptophan, and valine) or 3 positively charged polar groups (arginine, histidine, and lysine) did not. Starch proved to be nonessential.

Culture Media↗
PubMed2003

Lateral gene transfer and ancient paralogy of operons containing redundant copies of tryptophan-pathway genes in Xylella species and in heterocystous cyanobacteria.

BACKGROUND: Tryptophan-pathway genes that exist within an apparent operon-like organization were evaluated as examples of multi-genic genomic regions that contain phylogenetically incongruous genes and coexist with genes outside the operon that are congruous. A seven-gene cluster in Xylella fastidiosa includes genes encoding the two subunits of anthranilate synthase, an aryl-CoA synthetase, and trpR. A second gene block, present in the Anabaena/Nostoc lineage, but not in other cyanobacteria, contains a near-complete tryptophan operon nested within an apparent supraoperon containing other aromatic-pathway genes. RESULTS: The gene block in X. fastidiosa exhibits a sharply delineated low-GC content. This, as well as bias of codon usage and 3:1 dinucleotide analysis, strongly implicates lateral gene transfer (LGT). In contrast, parametric studies and protein tree phylogenies did not support the origination of the Anabaena/Nostoc gene block by LGT. CONCLUSIONS: Judging from the apparent minimal amelioration, the low-GC gene block in X. fastidiosa probably originated by LGT at a relatively recent time. The surprising inability to pinpoint a donor lineage still leaves room for alternative, albeit less likely, explanations other than LGT. On the other hand, the large Anabaena/Nostoc gene block does not seem to have arisen by LGT. We suggest that the contemporary Anabaena/Nostoc array of divergent paralogs represents an ancient ancestral state of paralog divergence, with extensive streamlining by gene loss occurring in the lineage of descent representing other (unicellular) cyanobacteria.

Amino Acid Sequence↗
PubMed2002

Genomics and X-ray microanalysis indicate that Ca2+ and thiols mediate the aggregation and adhesion of Xylella fastidiosa.

The availability of the genome sequence of the bacterial plant pathogen Xylella fastidiosa, the causal agent of citrus variegated chlorosis, is accelerating important investigations concerning its pathogenicity. Plant vessel occlusion is critical for symptom development. The objective of the present study was to search for information that would help to explain the adhesion of X. fastidiosa cells to the xylem. Scanning electron microscopy revealed that adhesion may occur without the fastidium gum, an exopolysaccharide produced by X. fastidiosa, and X-ray microanalysis demonstrated the presence of elemental sulfur both in cells grown in vitro and in cells found inside plant vessels, indicating that the sulfur signal is generated by the pathogen surface. Calcium and magnesium peaks were detected in association with sulfur in occluded vessels. We propose an explanation for the adhesion and aggregation process. Thiol groups, maintained by the enzyme peptide methionine sulfoxide reductase, could be active on the surface of the bacteria and appear to promote cell-cell aggregation by forming disulfide bonds with thiol groups on the surface of adjacent cells. The enzyme methionine sulfoxide reductase has been shown to be an auxiliary component in the adhesiveness of some human pathogens. The negative charge conferred by the ionized thiol group could of itself constitute a mechanism of adhesion by allowing the formation of divalent cation bridges between the negatively charged bacteria and predominantly negatively charged xylem walls.

Bacterial Adhesion↗
PubMed2001

Seasonal flight activity of two Homalodisca species (Homoptera: Cicadellidae) that spread Xylella fastidiosa in southern California.

Homalodisca coagulata (Say) and Homalodisca lacerta (Fowler) are vectors of a new bacterial disease of oleander in California known as oleander leaf scorch, induced by the bacterium Xylella fastidiosa. H. coagulata also has been implicated in the spread of the strain of X. fastidiosa that induces Pierce's disease of grapevines in California. We monitored the flight activity of H. coagulata and H. lacerta in oleander and citrus by using yellow sticky cards at three southern California locations where outbreaks of oleander leaf scorch have been documented, and where vector compliments are different. Areas sampled included a mesic coastal area (Irvine, CA) that supports predominantly H. coagulata and few H. lacerta, a dry inland location (Palm Desert, CA) that supports predominantly H. lacerta and few H. coagulata, and an intermediate area (Riverside, CA) supporting both Homalodisca species. From November 1996 to October 1999 peak catches of both Homalodisca species occurred during the midsummer at all locations. H. coagulata was trapped in greater numbers in citrus than in oleander at both the Riverside and the Irvine sites. Likewise, H. lacerta in Riverside was more associated with citrus than oleander, yet H. lacerta in Palm Desert was trapped in greater numbers in oleander than citrus.

Animals↗
PubMed2026

Nationwide Survey Using Real-Time PCR in 2024 and 2025 Supports the Absence of Xylella fastidiosa in Korea.

Xylella fastidiosa is a plant-pathogenic bacterium that causes severe diseases in economically important crops, such as citrus and grapevine, thereby posing a significant threat to global agriculture. Although X. fastidiosa has not yet been reported in Korea, the increase in international trade and its presence in neighboring countries highlight the necessity of continued surveillance. The objective of this study was to verify the absence of X. fastidiosa in Korea and to establish a reliable diagnostic framework through a nationwide survey conducted in 2024 and 2025. The sampling design was generated using the RiBESS+ statistical model to ensure the reliability of the survey results. Host plants, including grapevines (Vitis vinifera), mandarin oranges (Citrus unshiu), and cherry blossoms (Prunus yedoensis), were selected and sampled from urban and agricultural areas throughout the country for a nationwide survey. Genomic DNA was extracted from plant petioles and analyzed using real-time PCR with an optimized primer set (XF16S-F/R). Over a period of two years, a total of 2,314 samples were collected, exceeding the required sample size of 843 per year. X. fastidiosa was not detected in any of the collected and tested samples. These results confirm the absence of X. fastidiosa in Korea throughout the study period with high statistical confidence. This study provides evidence confirming the absence of X. fastidiosa in Korea and proposes a standardized methodology for future surveillance and early detection of other invasive prohibited quarantine pests.

X. fastidiosa↗
PubMed2004

Evaluation of methods for extracting Xylella fastidiosa DNA from the glassy-winged sharpshooter.

The recent spread of the plant pathogenic bacterium Xylclla fastidiosa Wells et al. by an invasive vector species, Homalodisca coagulata Say, in southern California has resulted in new epidemics of Pierce's disease of grapevine. Our goal is to develop an efficient method to detect low titers of X. fastidiosa in H. coagulata that is amenable to large sample sizes for epidemiological studies. Detection of the plant pathogenic bacterium X. fastidiosa in its insect vector is complicated by low titers of bacteria, difficulty in releasing it from the insect mouthparts and foregut, and the presence of substances in the insect that inhibit polymerase chain reaction (PCr). To select the optimal protocol for DNA extraction to be used with PCR, we compared three standard methods and 11 commercially available kits for relative efficiency of X. fastidiosa DNA extraction in the presence of insect tissue. All of the protocols tested were proficient at extracting DNA from pure bacterial culture (1 x 10(5) cells), and all but one protocol successfully extracted sufficient bacterial DNA in the presence of insect tissue. Three DNA extraction techniques, immunomagnetic separation, the DNeasy Tissue kit (Qiagen, Hercules, CA), and Genomic DNA Purification kit (Fermentus, Hanover, MD), were compared more closely using a dilution series of X. fastidiosa (5000-0 cells) with and without insect tissue present. The DNeasy Tissue kit was the best kit tested, allowing detection of 5 x 10(3) X. fastidiosa cells with an insect head background.

Animals↗
PubMed2003

Dispersion of Homalodisca coagulata (Hemiptera: Cicadellidae), a vector of Xylella fastidiosa, into vineyards in southern California.

Recent epidemics of Pierce's disease of grapevine in California vectored by Homalodisca coagulata (Say), an invasive vector species, have characteristics that differ from epidemics involving native vectors. Among these differences are the longer distances and greater speed that the disease is spread by H. coagulata. In this investigation, we used yellow sticky traps to study the seasonal dispersion activity of H. coagulata in a southern California grape-growing area in which an epidemic of Pierce's disease has caused large losses. For 21 mo, we monitored adult H. coagulata at the edges of vineyards bordering citrus, an important crop host, natural coastal sage scrub vegetation, and natural riparian vegetation. We also monitored H. coagulata dispersion from 0 to 40 m into vineyards. Finally, we examined the vertical dispersion of H. coagulata adults into grapevines through a season. This investigation showed that H. coagulata is associated with citrus, from where it disperses deep into vineyards, and not just the vineyard edge as with Pierce's disease vectors that are native to California. Peak dispersion into vineyards occurred in the summer. Another period of H. coagulata activity occurred in the winter in vineyards bordering citrus. Through the period of peak flight activity, 97% of all H. coagulata adults trapped between 1 and 7 m were caught at an altitude of 5 m or lower, suggesting the potential of a barrier as a management tactic to keep H. coagulata out of vineyards.

Animals↗
PubMed2026

Pathogen local adaptation shapes Pierce's disease of grapevines outcomes under field conditions.

Climate change is broadly expected to increase the range of many plant diseases, yet the current status of local thermal adaptation in many pathogens is poorly understood. Xylella fastidiosa (Xf) is a global bacterial plant pathogen that causes Pierce's disease (PD) of grapevines and infects over 700 other host plant species, impacting both agricultural and natural ecosystems. In a common garden experiment with 477 vines in the field, we compared PD outcomes from a local (colder climate in CA) vs non-local (warmer climate in CA) bacterial strain in 13 Mediterranean grapevine varieties over 3 years. Relative to the local strain, there was 77% lower overwinter survival in the non-local strain from a warmer climate, strongly indicating local adaptation in these CA Xf populations. Host genotype also had a significant effect on pathogen winter survival, and grapevine varieties differed in PD susceptibility. Additionally, we assessed in planta evolution of the two pathogen strains over 3 years by whole-genome sequencing 58 field-derived isolates. There were convergent loss-of-function mutations in genes encoding minor Type IV pilin (T4P) proteins, which control twitching motility and other virulence phenotypes, suggesting rapid adaptive evolution. Our results suggest local adaptation to cold temperatures in a bacterial plant pathogen and a possible role for minor Type IV pilins in thermal adaptation. These findings demonstrate the urgent need to incorporate X. fastidiosa evolution and local thermal adaptation into global models of PD spread. Differentiating pathotypes with distinct thermal adaptations will improve disease forecasting and inform quarantine decisions.IMPORTANCEForecasting the movement of plant pathogens is a critical issue under global warming to effectively manage future plant disease outbreaks. Yet, current plant pathogen local thermal adaptation is often unaccounted for, especially in bacterial pathogens. Our study examines local adaptation to temperature in a bacterial plant pathogen, Xylella fastidiosa, that causes disease in grapevines in addition to infecting 700 other plant species. In a large-scale field experiment across 13 grapevine varieties, we demonstrate local adaptation in pathogen winter survival in distinct Xylella fastidiosa strains. Additionally, we found evidence of adaptive evolution in just 3 years, as we observed convergent mutations after resequencing strains that evolved in the field. Our results suggest that X. fastidiosa populations-even within a small geographic area-have distinct adaptations to winter temperatures and may exhibit differential responses to warming winters.

Type IV pili↗
PubMed2004

Delivery of a genetically marked Alcaligenes sp. to the glassy-winged sharpshooter for use in a paratransgenic control strategy.

An artificial feeding system was designed for the glassy-winged sharpshooter (GWSS), Homalodisca coagulata Say (Hemiptera: Cicadellidae). The system, unlike previous systems, provided enough nutrients to GWSS to survive for 48 h. A system like this is a prerequisite to examining the potential use of paratransgenesis to interrupt transmission of Xylella fastidiosa, the bacterial pathogen causing Pierce's disease of grape, by insect vectors. We developed a system for short-term feeding of GWSS that allows for the introduction of bacteria in liquid medium, and we have demonstrated the ability of Alcaligenes xylosoxidans denitrificans, expressing a red fluorescent protein (dsRed), to colonize the cibarial region of the GWSS foregut for up to 5 weeks post-exposure. Alcaligenes xylosoxidans denitrificans thus occupies the same region in the foregut as the pathogen, Xylella fastidiosa.

Alcaligenes↗
PubMed2005

Rapid, specific and quantitative assays for the detection of the endophytic bacterium Methylobacterium mesophilicum in plants.

Xylella fastidiosa is a xylem-limited bacterium that causes citrus variegated chlorosis disease in sweet orange. There is evidence that X. fastidiosa interacts with endophytic bacteria present in the xylem of sweet orange, and that these interactions, particularly with Methylobacterium mesophilicum, may affect disease progress. However, these interactions cannot be evaluated in detail until efficient methods for detection and enumeration of these bacteria in planta are developed. We have previously developed standard and quantitative PCR-based assays specific for X. fastidiosa using the LightCycler system [Li, W.B., Pria Jr., L.P.M.W.D., X. Qin, and J.S. Hartung, 2003. Presence of Xylella fastidiosa in sweet orange fruit and seeds and its transmission to seedlings. Phytopathology 93:953-958.], and now report the development of both standard and quantitative PCR assays for M. mesophilicum. The assays are specific for M. mesophilicum and do not amplify DNA from other species of Methylobacterium or other bacteria commonly associated with citrus or plant tissue. Other bacteria tested included Curtobacterium flaccumfaciens, Pantoea agglomerans, Enterobacter cloacae, Bacillus sp., X. fastidiosa, Xanthomonas axonopodis pv. citri, and Candidatus Liberibacter asiaticus. We have demonstrated that with these methods we can quantitatively monitor the colonization of xylem by M. mesophilicum during the course of disease development in plants artificially inoculated with both bacteria.

Citrus sinensis↗
PubMed2002

An evolutionary perspective of Pierce's disease of grapevine, citrus variegated chlorosis, and mulberry leaf scorch diseases.

Xylella fastidiosa causes diseases on a growing list of economically important plants. An understanding of how xylellae diseases originated and evolved is important for disease prevention and management. In this study, we evaluated the phylogenetic relationships of X. fastidiosa strains from citrus, grapevine, and mulberry through the analyses of random amplified polymorphic DNAs (RAPDs) and conserved 16S rDNA genes. RAPD analysis emphasized the vigorous genome-wide divergence of X. fastidiosa and detected three clonal groups of strains that cause Pierce's disease (PD) of grapevine, citrus variegated chlorosis (CVC), and mulberry leaf scorch (MLS). Analysis of 16S rDNA sequences also identified the PD and CVC groups, but with a less stable evolutionary tree. MLS strains were included in the PD group by the 16S rDNA analysis. The Asiatic origins of the major commercial grape and citrus cultivars suggest the recent evolution of both PD and CVC disease in North and South America, respectively, since X. fastidiosa is a New World organism. In order to prevent the development of new diseases caused by X. fastidiosa, it is important to understand the diversity of X. fastidiosa strains, how strains of X. fastidiosa select their hosts, and their ecological roles in the native vegetation.

Citrus↗
PubMed2006

Refined mapping of the Pierce's disease resistance locus, PdR1, and Sex on an extended genetic map of Vitis rupestris x V. arizonica.

A framework genetic map based on genomic DNA-derived SSR, EST-derived SSR, EST-STS and EST-RFLP markers was developed using 181 genotypes generated from D8909-15 (female) x F8909-17 (male), the '9621' population. Both parents are half siblings with a common female parent, Vitis rupestris 'A. de Serres', and different male parents (forms of V. arizonica). A total of 542 markers were tested, and 237 of them were polymorphic for the female and male parents. The female map was developed with 159 mapped markers covering 865.0 cM with an average marker distance of 5.4 cM in 18 linkage groups. The male map was constructed with 158 mapped molecular markers covering 1055.0 cM with an average distance of 6.7 cM in 19 linkage groups. The consensus '9621' map covered 1154.0 cM with 210 mapped molecular markers in 19 linkage groups, with average distance of 5.5 cM. Ninety-four of the 210 markers on the consensus map were new. The 'Sex' expression locus segregated as single major gene was mapped to linkage group 2 on the consensus and the male map. PdR1, a major gene for resistance to Pierce's disease, caused by the bacterium Xylella fastidiosa, was mapped to the linkage group 14 between markers VMCNg3h8 and VVIN64, located 4.3 and 2.7 cM away from PdR1, respectively. Differences in segregation distortion of markers were also compared between parents, and three clusters of skewed markers were observed on linkage groups 6, 7 and 14.

Chromosome Mapping↗
PubMed2006

Identification of genomic islands in six plant pathogens.

Genomic islands (GIs) play important roles in microbial evolution, which are acquired by horizontal gene transfer. In this paper, the GIs of six completely sequenced plant pathogens are identified using a windowless method based on Z curve representation of DNA sequences. Consequently, four, eight, four, one, two and four GIs are recognized with the length greater than 20-Kb in plant pathogens Agrobacterium tumefaciens str. C58, Rolstonia solanacearum GMI1000, Xanthomonas axonopodis pv. citri str. 306 (Xac), Xanthomonas campestris pv. campestris str. ATCC33913 (Xcc), Xylella fastidiosa 9a5c and Pseudomonas syringae pv. tomato str. DC3000, respectively. Most of these regions share a set of conserved features of GIs, including an abrupt change in GC content compared with that of the rest of the genome, the existence of integrase genes at the junction, the use of tRNA as the integration sites, the presence of genetic mobility genes, the difference of codon usage, codon preference and amino acid usage, etc. The identification of these GIs will benefit the research for the six important phytopathogens.

Agrobacterium tumefaciens↗
PubMed2006

Correlation of stylet activities by the glassy-winged sharpshooter, Homalodisca coagulata (Say), with electrical penetration graph (EPG) waveforms.

Glassy-winged sharpshooter, Homalodisca coagulata (Say), is an efficient vector of Xylella fastidiosa (Xf), the causal bacterium of Pierce's disease, and leaf scorch in almond and oleander. Acquisition and inoculation of Xf occur sometime during the process of stylet penetration into the plant. That process is most rigorously studied via electrical penetration graph (EPG) monitoring of insect feeding. This study provides part of the crucial biological meanings that define the waveforms of each new insect species recorded by EPG. By synchronizing AC EPG waveforms with high-magnification video of H. coagulata stylet penetration in artifical diet, we correlated stylet activities with three previously described EPG pathway waveforms, A1, B1 and B2, as well as one ingestion waveform, C. Waveform A1 occured at the beginning of stylet penetration. This waveform was correlated with salivary sheath trunk formation, repetitive stylet movements involving retraction of both maxillary stylets and one mandibular stylet, extension of the stylet fascicle, and the fluttering-like movements of the maxillary stylet tips. Waveform B1 was ubitquious, interspersed throughout the other waveforms. B1 sub-type B1w was correlated with salivation followed by maxillary tip fluttering. This tip fluttering also occurred before and during B1 sub-type B1s, but was not directly correlated with either the occurrence or frequency of this waveform. Waveform B2 was correlated with sawing-like maxillary stylet movements, which usually occurred during salivary sheath branching. Waveform C was correlated with ingestion. Fluid outflow was also observed as a mechanism to clear the maxillary tips from debris during waveform C. This detailed understanding of stylet penetration behaviors of H. coagulata is an important step toward identifying the instant of bacterial inoculation which, in turn, will be applied to studies of disease epidemiology and development of host plant resistance.

Animals↗
PubMed2005

Application of a spotting sample preparation technique for the detection of pathogens in woody plants by RT-PCR and real-time PCR (TaqMan).

An extraction technique for reverse transcription-PCR (RT-PCR) detection of plant pathogens including viruses, bacteria and phytoplasma is described. The total nucleic acid of these plant pathogens was obtained by direct spotting of crude sap derived from infected leaf, petiole or cambial tissue onto two different types of membranes, positively charged Hybond N(+) Nylon and FTA membranes, and processed for use in PCR. Thirteen different plant viruses, Xylella fastidiosa (causal agent of Pierce's disease) and phytoplasmas were included in the experiment. A thermal treatment (95 degrees C for 10 min) of the Hybond N(+) Nylon discs in a buffered solution improved the detection, but for FTA membrane discs the thermal treatment was not required and the discs were directly placed in the PCR reaction cocktail. Specific amplification of genomic or ribosomal RNA fragments of these pathogens was obtained by one-step RT-PCR except for X. fastidiosa in which a fragment of the genomic DNA was used for amplification. The same sample preparation methods also worked well for real-time RT-PCR (TaqMan). The sample preparation techniques reported here could be used to store samples for future PCR test or for long distance shipment to a detection laboratory.

Edetic Acid↗
PubMed2006

Xylem structure and connectivity in grapevine (Vitis vinifera) shoots provides a passive mechanism for the spread of bacteria in grape plants.

BACKGROUND AND AIMS: Bacterial leaf scorch occurring in a number of economically important plants is caused by the xylem-limited bacterium Xylella fastidiosa (Xf). In grapevine, Xf systemic infection causes Pierce's disease and is lethal. Traditional dogma is that Xf movement between vessels requires the digestion of inter-vessel pit membranes. However, Yersinia enterocolitica (Ye) (a bacterium found in animals) and fluorescent beads moved rapidly within grapevine xylem from stem into leaf lamina, suggesting open conduits consisting of long, branched xylem vessels for passive movement. This study builds on and expands previous observations on the nature of these conduits and how they affect Xf movement. METHODS: Air, latex paint and green fluorescence protein (GFP)-Xf were loaded into leaves and followed to confirm and identify these conduits. Leaf xylem anatomy was studied to determine the basis for the free and sometimes restricted movement of Ye, beads, air, paint and GFP-Xf into the lamina. KEY RESULTS: Reverse loading experiments demonstrated that long, branched xylem vessels occurred exclusively in primary xylem. They were observed in the stem for three internodes before diverging into mature leaves. However, this stem-leaf connection was an age-dependent character and was absent for the first 10-12 leaves basal to the apical meristem. Free movement in leaf blade xylem was cell-type specific with vessels facilitating movement in the body of the blade and tracheids near the leaf margin. Air, latex paint and GFP-Xf all moved about 50-60% of the leaf length. GFP-Xf was never observed close to the leaf margin. CONCLUSIONS: The open vessels of the primary xylem offered unimpeded long distance pathways bridging stem to leaves, possibly facilitating the spread of bacterial pathogens in planta. GFP-Xf never reached the leaf margins where scorching appeared, suggesting a signal targeting specific cells or a toxic build-up at hydathodes.

Air↗