Zebra Chip (ZC) is an emerging plant disease that causes aboveground decline of potato shoots and generally results in unusable tubers. This disease has led to multi-million dollar losses for growers ...in the central and western United States over the past decade and impacts the livelihood of potato farmers in Mexico and New Zealand. ZC is associated with ‘ Candidatus Liberibacter solanacearum’, a fastidious alpha-proteobacterium that is transmitted by a phloem-feeding psyllid vector, Bactericera cockerelli Sulc. Research on this disease has been hampered by a lack of robust culture methods and paucity of genome sequence information for ‘ Ca. L. solanacearum’. Here we present the sequence of the 1.26 Mbp metagenome of ‘ Ca. L. solanacearum’, based on DNA isolated from potato psyllids. The coding inventory of the ‘ Ca. L. solanacearum’ genome was analyzed and compared to related Rhizobiaceae to better understand ‘ Ca. L. solanacearum’ physiology and identify potential targets to develop improved treatment strategies. This analysis revealed a number of unique transporters and pathways, all potentially contributing to ZC pathogenesis. Some of these factors may have been acquired through horizontal gene transfer. Taxonomically, ‘ Ca. L. solanacearum’ is related to ‘ Ca. L. asiaticus’, a suspected causative agent of citrus huanglongbing, yet many genome rearrangements and several gene gains/losses are evident when comparing these two Liberibacter. species. Relative to ‘ Ca. L. asiaticus’, ‘ Ca. L. solanacearum’ probably has reduced capacity for nucleic acid modification, increased amino acid and vitamin biosynthesis functionalities, and gained a high-affinity iron transport system characteristic of several pathogenic microbes.
Huanglongbing (HLB) is a highly destructive citrus disease which threatens citrus production worldwide and 'Candidatus Liberibacter asiaticus' (Las), a non-culturable phloem-limited bacterium, is an ...associated causal agent of the disease. To better understand the physiological and molecular processes involved in host responses to Las, 2-DE and mass spectrometry analyses, as well as ICP spectroscopy analysis were employed to elucidate the global protein expression profiles and nutrient concentrations in leaves of Las-infected grapefruit plants at pre-symptomatic or symptomatic stages for HLB.
This study identified 123 protein spots out of 191 spots that showed significant changes in the leaves of grapefruit plants in response to Las infection and all identified spots matched to 69 unique proteins/peptides. A down-regulation of 56 proteins including those associated with photosynthesis, protein synthesis, and metabolism was correlated with significant reductions in the concentrations of Ca, Mg, Fe, Zn, Mn, and Cu in leaves of grapefruit plants in response to Las infection, particularly in symptomatic plants. Oxygen-evolving enhancer (OEE) proteins, a PSI 9 kDa protein, and a Btf3-like protein were among a small group of proteins that were down-regulated in both pre-symptomatic and symptomatic plants in response to Las infection. Furthermore, a Las-mediated up-regulation of 13 grapefruit proteins was detected, which included Cu/Zn superoxide dismutase, chitinases, lectin-related proteins, miraculin-like proteins, peroxiredoxins and a CAP 160 protein. Interestingly, a Las-mediated up-regulation of granule-bound starch synthase was correlated with an increase in the K concentrations of pre-symptomatic and symptomatic plants.
This study constitutes the first attempt to characterize the interrelationships between protein expression and nutritional status of Las-infected pre-symptomatic or symptomatic grapefruit plants and sheds light on the physiological and molecular mechanisms associated with HLB disease development.
Little is known about specific host chemistry effects on zebra chip disease symptom development in potatoes (Solanum tuberosum). This research compared chemical profiles and defense-related enzyme ...levels between non-symptomatic and zebra chip-symptomatic potato tubers. Levels of phenolics, five amino acids, peroxidases, polyphenol oxidases, chitinases, and β-1,3-glucanases were greater in symptomatic tubers than non-symptomatic tubers, and many of these compounds also were positively correlated with zebra chip disease severity. ‘Candidatus Liberibacter solanacearum’ was consistently present in symptomatic tubers. However, the lack of associations between titers and tuber chemistry suggests a complicated relationship between this bacterium and zebra chip symptoms.
► Specific changes in tuber physiology may result in zebra chip symptom formation. ► Symptomatic tubers were analyzed for phenolics, amino acids, and defense proteins. ► Phenolic and amino acid levels were greater in symptomatic than non-symptomatic tubers. ► Defense-associated protein activity was also greater in symptomatic tubers. ► Increases in these compounds are associated with zebra chip symptom development.
Crown gall disease, caused by the soil bacterium Agrobacterium tumefaciens, results in significant economic losses in perennial crops worldwide. A. tumefaciens is one of the few organisms with a well ...characterized horizontal gene transfer system, possessing a suite of oncogenes that, when integrated into the plant genome, orchestrate de novo auxin and cytokinin biosynthesis to generate tumors. Specifically, the iaaM and ipt oncogenes, which show ≈90% DNA sequence identity across studied A. tumefaciens strains, are required for tumor formation. By expressing two self-complementary RNA constructions designed to initiate RNA interference (RNAi) of iaaM and ipt, we generated transgenic Arabidopsis thaliana and Lycopersicon esculentum plants that are highly resistant to crown gall disease development. In in vitro root inoculation bioassays with two biovar I strains of A. tumefaciens, transgenic Arabidopsis lines averaged 0.0-1.5% tumorigenesis, whereas wild-type controls averaged 97.5% tumorigenesis. Similarly, several transformed tomato lines that were challenged by stem inoculation with three biovar I strains, one biovar II strain, and one biovar III strain of A. tumefaciens displayed between 0.0% and 24.2% tumorigenesis, whereas controls averaged 100% tumorigenesis. This mechanism of resistance, which is based on mRNA sequence homology rather than the highly specific receptor-ligand binding interactions characteristic of traditional plant resistance genes, should be highly durable. If successful and durable under field conditions, RNAi-mediated oncogene silencing may find broad applicability in the improvement of tree crop and ornamental rootstocks.
Huanglongbing (HLB) is one of the most destructive citrus diseases in the world. The disease is associated with the presence of a fastidious, phloem-limited α- proteobacterium, 'Candidatus ...Liberibacter asiaticus', 'Ca. Liberibacter africanus' or 'Ca. Liberibacter americanus'. HLB-associated Liberibacters have spread to North America and South America in recent years. While the causal agents of HLB have been putatively identified, information regarding the worldwide population structure and epidemiological relationships for 'Ca. L. asiaticus' is limited. The availability of the 'Ca. L. asiaticus' genome sequence has facilitated development of molecular markers from this bacterium. The objectives of this study were to develop microsatellite markers and conduct genetic analyses of 'Ca. L. asiaticus' from a worldwide collection. Two hundred eighty seven isolates from USA (Florida), Brazil, China, India, Cambodia, Vietnam, Taiwan, Thailand, and Japan were analyzed.
A panel of seven polymorphic microsatellite markers was developed for 'Ca. L. asiaticus'. Microsatellite analyses across the samples showed that the genetic diversity of 'Ca. L. asiaticus' is higher in Asia than Americas. UPGMA and STRUCTURE analyses identified three major genetic groups worldwide. Isolates from India were genetically distinct. East-southeast Asian and Brazilian isolates were generally included in the same group; a few members of this group were found in Florida, but the majority of the isolates from Florida were clustered separately. eBURST analysis predicted three founder haplotypes, which may have given rise to three groups worldwide.
Our results identified three major genetic groups of 'Ca. L. asiaticus' worldwide. Isolates from Brazil showed similar genetic makeup with east-southeast Asian dominant group, suggesting the possibility of a common origin. However, most of the isolates recovered from Florida were clustered in a separate group. While the sources of the dominant 'Ca. L. asiaticus' in Florida were not clearly understood, the less-pervasive groups may have been introduced directly from Asia or via Brazil. Notably, the recent outbreak of HLB in Florida probably occurred through multiple introductions. Microsatellite markers developed in this study provide adequate discriminatory power for the identification and differentiation of closely-related isolates, as well as for genetic studies of 'Ca. L. asiaticus'.
‘
Candidatus
Liberibacter solanacearum’ is associated with the Zebra Chip (ZC) disorder of potatoes. A panel of eight simple sequence repeat (SSR) markers was developed and used to genetically ...characterize ‘
Ca.
L. solanacearum’ strains obtained from ZC-affected potato plants in the United States and Mexico. The multilocus SSR markers in this study effectively differentiated genotypes and estimated genetic diversity of ‘
Ca.
L. solanacearum’ strains. Genotype assignment analyses identified two major lineages of ‘
Ca.
L. solanacearum’ in the North American populations while only one lineage type was identified in Mexican population. No clear genetic structure was found among haplotypes based on geographical proximity or host. The high resolution power of the SSR marker system developed in this study provides a useful tool for genotyping closely related strains and tracking sources of the pathogen. Genotype information combined with epidemiological data will advance knowledge of ZC disease and will facilitate development of effective disease management.
We report here the complete genome sequence of "Candidatus Liberibacter africanus" strain PTSAPSY. The 1,192,232-bp genome with 34.5% G+C content comprises 1,017 open reading frames, 44 tRNAs, and ...three complete rRNAs in a circular chromosome.
Xylella fastidiosa causes disease in many commercial crops, including almond leaf scorch (ALS) disease in susceptible almond (Prunus dulcis). In this study, genetic diversity and population structure ...of X. fastidiosa associated with ALS disease were evaluated. Isolates obtained from two almond orchards in Fresno and Kern County in the San Joaquin Valley of California were analyzed for two successive years. Multilocus simple-sequence repeat (SSR) analysis revealed two major genetic clusters that were associated with two host cultivars, 'Sonora' and 'Nonpareil', respectively, regardless of the year of study or location of the orchard. These relationships suggest that host cultivar selection and adaptation are major driving forces shaping ALS X. fastidiosa population structure in the San Joaquin Valley. This finding will provide insight into understanding pathogen adaptation and host selection in the context of ALS disease dynamics.
Xylella fastidiosa is an important pathogen of many commercial crops. Detection of X. fastidiosa is difficult due to low concentrations of the bacteria in insects and asymptomatic plant tissue, and ...non-uniform distribution in infected plants. A dual purpose conventional PCR and quantitative PCR (TaqMan(TM)) system was developed for the generic detection of X. fastidiosa strains. Primers HL5 and HL6, designed to amplify a unique region common to the sequenced genomes of four Xylella strains, amplified a 221 bp fragment from strains associated with Pierce's disease of grapes, almond leaf scorch, and oleander leaf scorch disease and from DNA from an Xf strain associated with citrus variegated chlorosis. Standard curves were obtained using concentrations of Xylella ranging from 5 to 10^sup 5^ cells per reaction in water and grape extracts and 10-10^sup 5^ cells in insect DNA. Regression curves were similar, with correlation coefficients of r ^sup 2^>0.97. In quantitative PCR, C^sub t^ values ranged between 20 and 36 cycles for 5-10^sup 5^ bacterial cells per reaction. No amplicons were obtained with several non-Xf bacterial strains tested including related plant pathogenic, grape endophytic bacteria and endosymbiotic bacteria isolated from glassy-winged sharpshooters. The method was evaluated for clinical diagnosis of Xf in grapes, almonds and insect vectors. The procedure described is reliable for detection of the pathogen with a high degree of sensitivity and specificity.PUBLICATION ABSTRACT
Use of Nutshells as Fillers in Polymer Composites Sutivisedsak, Nongnuch; Cheng, Huai N; Burks, Charles S ...
Journal of polymers and the environment,
06/2012, Letnik:
20, Številka:
2
Journal Article
Recenzirano
Nutshells are agricultural waste products that can be procured at relatively low cost. In this work we examined the possibility of using these biodegradable materials as fillers in poly(lactic acid) ...and low density polyethylene. The nutshells were ground into powder, blended with the polymer, and then injection molded with final weight varying from 10 to 40 weight %. The mechanical and thermal properties of the composites were then studied. In general, the addition of fillers caused reductions in mechanical properties to varying extents, but thermal properties were only slightly affected. The use of maleic anhydride and peroxide with the fillers had a negative effect on poly(lactic acid) but a slightly positive effect on the stiffness of polyethylene. The results suggested that polymer-nutshell composites may be usable in applications where cost is a concern and where some reductions in mechanical properties are acceptable.
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