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Tissue-specific transcriptomic profiling of ‘Candidatus Liberibacter asiaticus’ in citrus reveals novel insights into Huanglongbing pathogenesis

ABSTRACT: ‘Candidatus Liberibacter asiaticus’ (Las) is a gram-negative bacterial pathogen associated with citrus huanglongbing (HLB) or greening disease. Las is transmitted by the Asian citrus psyllid (ACP) where it colonizes the phloem tissue, resulting in substantial economic losses to citrus industry worldwide. Despite extensive efforts, effective management strategies against HLB remain elusive, necessitating a deeper understanding of the pathogen’s biology. Las undergoes cell-to-cell movement through phloem flow from source to sink tissues and these tissues have varying responses to Las infection. Here, we investigate the transcriptomic landscape of Las in citrus sink tissues, particularly seed coat vasculatures, revealing more complete gene expression profiling of Las and unique transcriptomic pattern compared to previous studies using midrib tissues. Comparative transcriptomics between citrus seed coat vasculature and midrib tissues and ACP allowed the identification of tissue-specific responses and metabolic states of Las in planta. Furthermore, analysis of putative regulatory elements uncovers the potential role of LuxR-type transcription factors in regulating the expression of effector genes in citrus. We characterized two Las virulence factors that exhibit increased expression in seed coat vasculature tissue. Their ability to suppress different immune outputs was accessed and we demonstrate that they may contribute to the suppression of callose deposition during Las colonization. Moreover, this work provides novel insights into the pathogenesis of the devastating citrus HLB.

ORGANISM(S): Citrus x paradisi

PROVIDER: GSE270557 | GEO | 2024/06/30

REPOSITORIES: GEO

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Project description:Huanglongbing (HLB) (=citrus greening) is a destructive disease of citrus which is caused by a fastidious, phloem-inhabiting bacterium of the genus Candidatus Liberibacter. Large-scale analysis of gene expression changes in ‘Valencia’ orange leaves were studied during the course of 19 weeks after inoculation with Ca. L. asiaticus using the Affymetrix GeneChip® citrus genome array to provide new insights into the molecular basis of citrus response to this pathogen. Of the more than 33,000 probe sets on the microarray 21,067 were expressed in the leaves, of which 279 and 515 were differentially expressed (FDR ≤ 0.05) five to nine and 13-17 weeks after inoculation, respectively. Results from semi-quantitative RT-PCR analysis performed on 14 selected genes were highly correlated with those observed with the microarray. Gene expression changes involved a variety of different processes including cell defense, transport, cellular organization, photosynthesis, and carbohydrate metabolism. Notable was the pathogen-induced accumulation of transcripts for a phloem-specific lectin PP2-like protein. Transcriptional changes and their relation to disease symptom development are discussed. This is the first study of transcriptional profiling in citrus in response to liberibacter infection using microarray technology. Huanglongbing (HLB) is a destructive disease of citrus which is suspected to be caused by a phloem-inhabiting bacterium of the genus Candidatus Liberibacter. Large-scale analysis of gene expression changes in ‘Valencia’ orange (C. sinensis) leaves were studied during the course of 19 weeks after inoculation with Ca. L. asiaticus (Las), the pathogen associated with HLB in Florida, using the Affymetrix GeneChip® citrus genome array to provide new insights into the molecular basis of citrus response to this pathogen. Three year-old 'Valencia' orange (C. sinensis) scions on Cleopatra mandarin (C. reticulata Blanco) rootstocks were graft-inoculated with non-infected (control) or Las-infected tissue from greenhouse- (control) or field-grown 'Lisbon' lemon (C. limon) trees. Fully expanded leaves were collected at 5, 9, 13, and 17 weeks after inoculation (wai). Total RNA was extracted from two control plants and from three Las-inoculated plants per time point. Equal amounts of RNA were combined from samples collected 5 wai and 9 wai and from samples collected 13 wai and 17 wai, resulting in two non-infected and three infected biological replicates for both early (5-9 wai) and late (13-17 wai) time points and used for hybridization on Affymetrix citrus microarrays.

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Tissue-specific transcriptomic profiling of ‘Candidatus Liberibacter asiaticus’ in citrus reveals novel insights into Huanglongbing pathogenesis

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