title: 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.
authors.affiliation: University of Florida, IFAS, Horticultural Sciences Department, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850-2299, USA.
authors.forename: Hui-Ling
authors.initials: HL
authors.lastname: Liao
authors.forename: Jacqueline K
authors.initials: JK
authors.lastname: Burns
mesh_terms: D050260:Carbohydrate Metabolism / Q000235:genetics; D032084:Citrus sinensis / Q000235:genetics* / Q000382:microbiology*; D020224:Expressed Sequence Tags; D005638:Fruit / Q000033:anatomy & histology / Q000235:genetics* / Q000382:microbiology*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D009928:Organ Specificity / Q000235:genetics; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D018515:Plant Leaves / Q000382:microbiology; D058526:Plant Vascular Bundle / Q000235:genetics / Q000382:microbiology; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D012230:Rhizobiaceae / Q000502:physiology*; D014197:Trees / Q000382:microbiology*
chemical_list: D012336:RNA, Ribosomal, 16S