ABSTRACT: Crude extracts of 1L cultures of fungal and bacterial strains isolated from citrus trees under high HLB pressure, grown for 1 week. All showed in vitro inhibition of Liberibacter crescens.
Project description:HLB is suggested to be caused by the phloem-limited fastidious prokaryotic α-proteobacterium “Candidatus Liberibacter spp.” Previous studies focused on the proteome and transcriptome analyses of citrus 5 to 35-week-after “Ca. L. spp.” inoculation. In this study, gene expression profiles was analyzed using mandarin of Citrus reticulate Blanco cv. jiaogan leaves after 2-year infection with “Ca. L. asiaticus”. The Affymetrix GeneChip® citrus genome were applied to study the molecular pathways mediated by “Ca. L. asiaticus” inoculated 3-year-old jiaogan seedlings. Each of them was graft-inoculated with one sweet orange scions with or without “Ca. L. asiaticus” in Dectember, 2009. RNA samples from three mandarin trees infected with 'Candidatus Liberibacter asiaticus' and three uninfected trees were used for affymatrix genochip
Project description:Huanglongbing (HLB) is considered the most destructive disease in Citrus production and threatens the future of the industry. Microbial derived defence elicitors have gained recognition for their role in plant defence priming. A transcriptomic assessment using GeneChip microarray of the hour 6 samples revealed differential expression of 565 genes when MFA was applied to healthy trees and 909 genes when applied infected citrus trees when compared to their respective controls. There were 403 uniquely differentially expressed genes in response to MFA following an intersectional analysis of both healthy and infected citrus trees. The transcriptomic analysis revealed that several genes associated with plant development, growth and defence were upregulated in response to MFA, including, multiple PR genes, lignin formation genes, ROS related genes, hormone synthases and hormone regulators.
Project description:Devastating citrus disease Huanglongbing (HLB) is without existing cures. Herein, we present results demonstrating the possible mechanisms (hypoxia stress) behind HLB-triggered shoot dieback by comparing the transcriptomes, hormone profiles, and key enzyme activities in buds of severely and mildly symptomatic ‘Hamlin’ sweet orange (Citrus sinensis). Within six months (October – May) in field conditions, severe trees had 23% bud dieback, greater than mild trees (11%), with a concomitant reduction in canopy density. In February, differentially expressed genes (DEGs) associated with responses to osmotic stress, low oxygen levels, and cell death were upregulated, with those for photosynthesis and cell cycle downregulated in severe versus mild trees. For severe trees, not only were the key markers for hypoxia, including anaerobic fermentation, reactive oxygen species (ROS) production, and lipid oxidation, transcriptionally upregulated, but also alcohol dehydrogenase activity was significantly greater compared to mild trees, indicating a link between bud dieback and hypoxia. Tricarboxylic acid cycle revival, given the upregulation of glutamate dehydrogenase and alanine aminotransferase DEGs, suggests that ROS may also be generated during hypoxiareoxygenation. Greater (hormonal) ratios of abscisic acid to cytokinins and jasmonates and upregulated DEGs encoding NADPH oxidases in severe versus mild trees indicate additional ROS production under limited oxygen availability due to stomata closure. Altogether, our results provided evidence that as HLB progresses, excessive ROS produced in response to hypoxia and during hypoxia-reoxygenation likely intensify the oxidative stress in buds leading to cell death, contributing to marked bud and shoot dieback and decline of the severely symptomatic sweet orange trees.
Project description:Citrus greening or huanglongbing (HLB) is a devastating disease of citrus. HLB is associated with the phloem-limited fastidious prokaryotic alpha-proteobacterium Candidatus Liberibacter spp. In this report, we used sweet orange (Citrus sinensis) leaf tissue infected with 'Ca. Liberibacter asiaticus' and compared this with healthy controls. Investigation of the host response was examined with citrus microarray hybridization based on 30,171 sets expressed sequence tag sequences from several citrus species and hybrids. The microarray analysis indicated that HLB infection significantly affected expression of 624 genes whose encoded proteins were categorized according to function. The categories included genes associated with sugar metabolism, plant defense, phytohormone, and cell wall metabolism, as well as 14 other gene categories. Young, healthy Valencia sweet orange (C. sinensis) plants were graft inoculated with budwood from Ca. L. asiaticus-infected citrus plants. Prior to the innocualtion, the plants were confirmed to be Ca. L. asiaticus-free in ordinary and quantitative PCR tests. The presence of the bacteria in the inoculated plants was confirmed in both conventional and quantitative PCR with specific primers to Ca. L. asiaticus. The stem and root samples used for RNA extraction and hybridization on Affymetrix microarrays were obtained from three symptomatic and three healthy control trees of similar size, approximately 1 year after inoculation.
Project description:To evaluate the transcriptome response of roots towards Hoagland solution of two-year-old healthy (C) and HLB-affected (T) sweet orange (Citrus sinensis L.) cultivar Midsweet grafted on Kuharskei Carrizo rootstock at three different time points; D1 (at the start of the experiment), D2 (After 3 days of Hoagland solution), D3 (After nine days of Hoagland solution), were performed using RNA sequencing analysis. A total of 9, 19, and 2324 DEGs were expressed in HLB-affected and healthy trees feeder roots on D1, D2, and D3, respectively. Due to a small number of DEGs in HLB-affected and healthy trees roots on D1 and D2, enrichment analysis could not be performed. At D3, Gene Ontology (GO) enrichment analysis was performed using upregulated and downregulated DEGs in HLB-affected roots compared to healthy roots. For the upregulated DEGs in HLB-affected roots, the most enriched biological GO categories were related to transport, cellular amino acid metabolic process, oxoacid metabolic process, organic acid metabolic processes, phenylpropanoid biosynthesis process, response to carbohydrate stimulus, ethylene and the jasmonic acid-mediated signaling pathway, and regulation of plant hormone. The biological GO categories based on the number of DEGs associated with downregulated DEGs were the developmental process, phosphate metabolic process, protein modification process, defense response, growth, cell cycle, cell death, and ABA-mediated signaling pathway. The results of this study strongly suggest; although, the reduced biomass limits the nutrient uptake capacity in the plants as a whole, so in order to compensate for reduced root to shoot ratio the existing root undergo anatomical and transcriptomic changes to improve nutrient uptake efficiency to meet the nutrient demand of shoot systems. It is likely that higher inputs of energy in nutrient uptake possibly results in reducing the root longevity of HLB-affected trees. Good nutrition management practices are critical for the survival of HLB-affected trees as the availability and uptake of nutrients allow HLB-affected trees in response to abiotic and biotic stress.
Project description:HLB is suggested to be caused by the phloem-limited fastidious prokaryotic α-proteobacterium “Candidatus Liberibacter spp.” Previous studies focused on the proteome and transcriptome analyses of citrus 5 to 35-week-after “Ca. L. spp.” inoculation. In this study, gene expression profiles was analyzed using mandarin of Citrus reticulate Blanco cv. jiaogan leaves after 2-year infection with “Ca. L. asiaticus”.
Project description:Citrus Huanglongbing (HLB, or greening) is one of the most severe diseases of citrus. Plant disease symptom development is considered to be the consequence of a number of molecular, cellular and physiological changes, and may also be associated with host defense responses. Understanding citrus host response to HLB may contribute to the development of new strategies to control this destructive disease. We performed microarray analysis to identify the differentially expressed genes in sweet orange in response to HLB infection using the Affymetrix GeneChip® citrus genome array.
Project description:Huanglongbing (HLB) is a worldwide devastating disease of citrus. There are no effective control measures for this newly emerging but century-old disease. Previously, we reported a combination of Penicillin G and Streptomycin was effective in eliminating or suppressing the associated bacterium, M-bM-^@M-^XCandidatus Liberibacter asiaticusM-bM-^@M-^Y (Las). Here we report the bacterial composition and community structure in HLB-affected citrus plants during a growing season and while being treated with antibiotic combinations PS (Penicillin G and Streptomycin) and KO (Kasugamycin and Oxytetracycline) using the PhylochipM-bM-^DM-" G3 array. The antibiotic treatments were conducted on the randomized complete block design with four replicates. For each replicate, five HLB-affected, 7-year-old citrus trees (a unique hybrid, 10c-5-58, which is an open-pollinated seedling from the combination of Lee mandarin M-CM-^W Orlando tangelo) at the USHRL farm, 10 cm in diameter, were injected with either 100 ml of the antibiotic combination treatment PS (5 g of penicillin G potassium + 0.5 g of Streptomycin per tree) or the antibiotic treatment KO (2 g of oxytetracycline + 1.0 g of kasugamycin per tree). Five trees were injected with water as injection controls (CK). Injections were made using an Avo-Ject syringe injector (a catheter-tipped 60 ml syringe; Aongatete Coolstores Ltd., NZ) beginning in August of 2010. The tapered tip was firmly fitted into a 19/64-in (7.5 mm) diameter hole, M-bM-^IM-^H3 cm deep, drilled into the tree. The injector was kept in the tree and the treatment lasted for one week in each injection-trunk. Treatments were repeated every 2 months for one year and ceased in August of 2011. Before and during treatment more than 30 leaf samples per tree were taken from different positions around the tree canopies for qPCR assays at 2 month intervals.DNA for the PhyloChipM-bM-^DM-" G3 analysis, which was extracted from 20 samples of the same treatment, was pooled in equal amounts and quantified by the PicoGreenM-BM-. method. The PhyloChipTM G3 analysis was conducted by Second Genome Inc. (San Francisco, CA).
Project description:Citrus Huanglongbing (HLB, or greening) is one of the most severe diseases of citrus. Plant disease symptom development is considered to be the consequence of a number of molecular, cellular and physiological changes, and may also be associated with host defense responses. Understanding citrus host response to HLB may contribute to the development of new strategies to control this destructive disease. We performed microarray analysis to identify the differentially expressed genes in sweet orange in response to HLB infection using the Affymetrix GeneChipM-BM-. citrus genome array. Two-year-old seedlings of M-bM-^@M-^XMadam VinousM-bM-^@M-^Y sweet orange (Citrus sinensis L. Osbeck) were inoculated by grafting with bud sticks from HLB-diseased, PCR positive sweet orange plants. For mock-inoculated controls, the same types of plants were grafted with bud sticks from HLB-free, PCR negative sweet orange. At 7 months after inoculation, mature leaves were sampled from 3 individual HLB-diseased plants, and healthy leaves from 3 mock-inoculated plants as control. Total RNA was extracted from leaf samples and hybridized on Affymetrix microarrays.
Project description:Citrus greening or huanglongbing (HLB) is a devastating disease of citrus. HLB is associated with the phloem-limited fastidious prokaryotic alpha-proteobacterium Candidatus Liberibacter spp. In this report, we used sweet orange (Citrus sinensis) leaf tissue infected with 'Ca. Liberibacter asiaticus' and compared this with healthy controls. Investigation of the host response was examined with citrus microarray hybridization based on 30,171 sets expressed sequence tag sequences from several citrus species and hybrids. The microarray analysis indicated that HLB infection significantly affected expression of 624 genes whose encoded proteins were categorized according to function. The categories included genes associated with sugar metabolism, plant defense, phytohormone, and cell wall metabolism, as well as 14 other gene categories.