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Title: Gene expression in Citrus sinensis (L.) Osbeck following infection with the bacterial pathogen Candidatus Liberibacter asiaticus causing Huanglongbing in Florida

Author
item Albrecht, Ute
item Bowman, Kim

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2008
Publication Date: 5/16/2008
Citation: Albrecht, U., Bowman, K.D. 2008. Gene expression in Citrus sinensis (L.) Osbeck following infection with the bacterial pathogen Candidatus Liberibacter asiaticus causing Huanglongbing in Florida. Plant Science. 175(3):291-306.

Interpretive Summary: The large-scale expression of genes was studied in citrus plants after infection with the bacterium causing Huanglongbing or citrus greening disease in Florida and compared with non-infected plants. Of the thousands of genes analyzed using a gene chip many were found to be up- or down-regulated in response to bacterial infection. Several genes which are involved in carbohydrate metabolism, transport and cellular organization are described in more detail. Analyzing the response of citrus plants at the molecular level is the first step to understanding Huanglongbing and will contribute to the development of new control strategies to manage this destructive disease of citrus.

Technical Abstract: Hunglongbing (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 1,100 were differentially expressed (P = 0.05) within 5-9 weeks and 1,696 within 13-17 weeks after inoculation. Results from semi-quantitative RT-PCR analysis performed on selected genes were highly correlated with those observed with the microarray. Gene expression changes involved a variety of different cellular and metabolic processes of which some related to carbohydrate metabolism, transport and cellular organization are described in more detail. Among the transcripts highly induced 5-9 weeks after inoculation were those coding for enzymes of starch biosynthesis, glucose-6-phosphate/phosphate translocator and ADP-glucose pyrophosphorylase. Thirteen to 17 weeks after inoculation genes coding for proteins involved in cell organization, particularly expansins, and for proteins directly linked to symptom development, like ABC transporters and phloem-specific lectin PP2-like proteins were expressed abundantly. Transcripts for photosynthetic genes were down-regulated in response to infection. Additional RT-PCR analysis of selected genes in a second experiment with ‘Navel’ orange plants further confirmed these findings. This is the first study of transcriptional profiling in citrus in response to bacterial infection using microarray technology.