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Gene expression in Citrus sinensis fruit tissues harvested from huanglongbing-infected trees: comparison with girdled fruit.

ABSTRACT: Distribution of viable Candidatus Liberibacter asiaticus (CaLas) in sweet orange fruit and leaves ('Hamlin' and 'Valencia') and transcriptomic changes associated with huanglongbing (HLB) infection in fruit tissues are reported. Viable CaLas was present in most fruit tissues tested in HLB trees, with the highest titre detected in vascular tissue near the calyx abscission zone. Transcriptomic changes associated with HLB infection were analysed in flavedo (FF), vascular tissue (VT), and juice vesicles (JV) from symptomatic (SY), asymptomatic (AS), and healthy (H) fruit. In SY 'Hamlin', HLB altered the expression of more genes in FF and VT than in JV, whereas in SY 'Valencia', the number of genes whose expression was changed by HLB was similar in these tissues. The expression of more genes was altered in SY 'Valencia' JV than in SY 'Hamlin' JV. More genes were also affected in AS 'Valencia' FF and VT than in AS 'Valencia' JV. Most genes whose expression was changed by HLB were classified as transporters or involved in carbohydrate metabolism. Physiological characteristics of HLB-infected and girdled fruit were compared to differentiate between HLB-specific and carbohydrate metabolism-related symptoms. SY and girdled fruit were smaller than H and ungirdled fruit, respectively, with poor juice quality. However, girdling did not cause misshapen fruit or differential peel coloration. Quantitative PCR analysis indicated that many selected genes changed their expression significantly in SY flavedo but not in girdled flavedo. Mechanisms regulating development of HLB symptoms may lie in the host disease response rather than being a direct consequence of carbohydrate starvation.

SUBMITTER: Liao HL

PROVIDER: S-EPMC3350938 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:In this data set, we reported for the first time that huanglongbing disease (HLB) induces major changes in the expression of global genes in flavedo, vascular and juice vesicle tissues of citrus fruit. 68 Total samples were analyzed. cDNA generation, array analysis, and statistical tests were performed as a service at the Interdisciplinary Center for Biotechnology Research (ICBR) Microarray Core facility at the University of Florida (Gainesville, FL). The linear models were used for array analysis (Smyth GK et al. Bioinformatics, 2005, 2067-2075). The linear models were firstly used to assess differential expression, and then an empirical Bayes method was used to moderate the standard errors. 13 comparisons were performed for the study. The comparisons in Citrus sinensis cv. Hamlin included: SC vs. CC (genes that respond to infection in symptomatic vascular core); SJV vs. CJV (genes that respond to infection in symptomatic juice vesicle); SS vs. CS (genes that respond to infection in symptomatic seed); SP vs. CP (genes that respond to infection in symptomatic peel). The comparisons in Citrus sinensis cv. Valencia included: SP vs. HP (genes that respond to infection in symptomatic peel); ASP vs. HP (genes that respond to infection in asymptomatic peel); SP vs. ASP (genes that respond to infection in symptomatic peel compared to asymptomatic peel); SC vs. HC (genes that respond to infection in symptomatic vascular core); ASC vs. HC (genes that respond to infection in asymptomatic vascular core); SC vs. ASC (genes that respond to infection in symptomatic vascular core compared to asymptomatic vascular core); SJV vs. HJV (genes that respond to infection in symptomatic juice vesicle); ASJV vs. HJV (genes that respond to infection in asymptomatic juice vesicle); SJV vs. ASJV (genes that respond to infection in symptomatic juice vesicle compared to asymptomatic juice vesicle). ESTs with significant expression changes (P value <0.001; false discovery rate <0.01 with equal or higher than 2-fold changes in expression) were selected for further analysis.

Project description:Huanglongbing (HLB) is considered the most destructive disease in Citrus production and threatens the future of the industry. Microbial-derived defense elicitors have gained recognition for their role in plant defense priming. This work assessed a 5% (V/V) microbial fermentation application (MFA) and its role in the elicitation of defense responses in HLB-infected Citrus sinensis trees following a foliar application with a pump sprayer. Using a PCR detection method, HLB infection levels were monitored in healthy and infected trees for 20months. Nutrient analysis assessed N, P, K, Ca, Mg, Mn, Zn, Fe, B, and Cu concentrations in the trees. MFA significantly increased Cu concentrations in treated trees and resulted in the stabilization of disease index (DI) in infected trees. Initial real-time qPCR analysis of defense-associated genes showed a significant increase in pathogenesis-related protein 2 (PR2) and phenylalanine ammonia lyase (PAL) gene expression in healthy and HLB-infected trees in response to MFA. Gene expression of PR2 and PAL peaked 6h post-microbial fermentation application during an 8-h sampling period. 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 defense were upregulated in response to MFA, including multiple PR genes, lignin formation genes, ROS-related genes, hormone synthases, and hormone regulators. This study provides further evidence that MFA may play an important role as a plant elicitor in an integrated pest management strategy in citrus and other agronomically important crops.

Project description:Huanglongbing (HLB or Citrus Greening Disease) is a destructive citrus disease that has impacted the Florida citrus industry as well as global citrus industry for many years. There is yet to be a practical cure for HLB. Insecticide use targeting the psyllid vector and the burning, destruction and removal of all infected plants are the best solutions as of now. However, this is only a temporary and costly fix. The damage caused by HLB itself, the destruction of infected trees, and indirect effects in other economic sectors costs the Florida economy approximately $900 million per year. There are also problems with insecticide use; the high dosage needed the adequately suppress the transmission of the disease would contaminate the environment, rendering this solution unsustainable. Alternative solutions are needed. In the hopes of uncovering an alternative solution, we investigated the protein and phosphoprotein differences between healthy and diseased citrus plants to identify potential biomarkers essential towards fighting HLB within the trees themselves. For our experimental procedure, we grinded 2 grams of fresh leaf weight from the species Citrus sinensis (sweet orange). Phenol extraction was used to extract the proteins from four biological replicates of the control (healthy) leaves and four biological replicates of the treatment (diseased) leaves. Utilizing a Bradford assay and a 1-D gel electrophoresis, we evaluated the quality and quantity of the samples. Equal amounts of protein from the eight samples were digested with trypsin for 16 hours. Afterwards, we split each sample into two groups: one for phospho-enrichment and the other for total analysis. Phosphopeptides were enriched with the NuTip enrichment procedure for analysis of the phosphopeptides. Total peptides were cleaned up using ZipTip solid phase extraction. We ran the phosphopeptides and total peptides on an LC-MS/MS system, and the raw data files were processed with the Proteome Discoverer software using the citrus database downloaded from NCBI.

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Gene expression in Citrus sinensis fruit tissues harvested from huanglongbing-infected trees: comparison with girdled fruit.

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