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United States Department of Agriculture

Agricultural Research Service

Research Project: GENETIC IMPROVEMENT OF CITRUS

Location: Subtropical Insects and Horticulture Research

Title: Transcriptional response of susceptible and tolerant citrus to infection with Candidatus Liberibacter asiaticus

Authors
item Albrecht, Ute
item Bowman, Kim

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 8, 2011
Publication Date: September 8, 2011
Citation: Albrecht, U., Bowman, K.D. 2011. Transcriptional response of susceptible and tolerant citrus to infection with Candidatus Liberibacter asiaticus. Plant Science. 185-186:118-130.

Interpretive Summary: Candidatus Liberibacter asiaticus (Las) is non-culturable phloem-limited bacterium and the suspected causal agent of Huanglongbing (HLB) in Florida, one of the most devastating diseases of citrus. No resistant citrus cultivars have been identified to date, though tolerance has been observed in trifoliate orange (Poncirus trifoliata) and some of its hybrids. This study compares changes in gene expression in tolerant US-897 (Citrus reticulata x Poncirus trifoliata) and susceptible ‘Cleopatra’ mandarin (Citrus reticulata) seedlings in response to infection with Las. The main objective of the study was to identify genes associated with tolerance to HLB. After analysis using a citrus gene chip, several hundreds of genes were identified to be induced by at least four-fold in infected ‘Cleopatra’ seedlings. Only 17 genes were induced in US-897 upon infection. More than eight hundred genes were expressed at much higher levels in US-897 independent of infection with Las. Among these were several genes which were shown to be associated with disease resistance in a variety of plant-pathogen systems. The possible involvement of these genes in tolerance to HLB and their possible use for biotechnology are discussed.

Technical Abstract: Candidatus Liberibacter asiaticus (Las), a non-culturable phloem-limited bacterium, is the suspected causal agent of Huanglongbing (HLB) in Florida. HLB is one of the most devastating diseases of citrus and no resistant cultivars have been identified to date, though tolerance has been observed in the genus Poncirus and some of its hybrids. This study compares transcriptional changes in tolerant US-897 (Citrus reticulata Blanco x Poncirus trifoliata L. Raf.) and susceptible ‘Cleopatra’ mandarin (C. reticulata) seedlings in response to infection with Las using the Affymetrix GeneChip citrus array, with the main objective of identifying genes associated with tolerance to HLB. Microarray analysis identified several hundred genes significantly induced by at least four-fold in the susceptible genotype, compared with only 17 genes in US-897. Exclusively induced in US-897 was a gene for a 2-oxoglutarate (2OG) and Fe(II)-dependant oxygenase, an important enzyme involved in the biosynthesis of plant secondary metabolites. More than eight hundred genes were expressed at much higher levels in US-897 independent of infection with Las. Among these, genes for a constitutive disease resistance protein (CDR1) were notable. The possible involvement of these and other detected genes in tolerance to HLB and their possible use for biotechnology are discussed.

Last Modified: 7/23/2014
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