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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Molecular Plant Pathology Laboratory » Research » Publications at this Location » Publication #322973
Title: Transcriptome analysis of sweet orange trees infected with ‘Candidatus Liberibacter asiaticus’ and two strains of citrus tristeza virus

Author
item FU, SHIMIN - Southwest University
item Shao, Jonathan
item ZHOU, CHANGYONG - Southwest University
item Hartung, John

Submitted to: BMC Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2016
Publication Date: 5/11/2016
Citation: Fu, S., Shao, J.Y., Zhou, C., Hartung, J.S. 2016. Transcriptome analysis of sweet orange trees infected with ‘Candidatus Liberibacter asiaticus’ and two strains of citrus tristeza virus. BMC Genomics. 17:349. doi.10.1186/s12864-016-2663-9.

Interpretive Summary: Huanglongbing (HLB) and tristeza are diseases of sweet orange trees caused by a bacterium, and a virus respectively. HLB is a devastating disease, but tristeza strains vary from very severe to very mild. Both pathogens live only in the same plant tissues. Severe strains of tristeza induce symptoms similar to HLB, but mild strains of tristeza infect the tree without making any symptoms. The presence of either pathogen and the induction of symptoms change the expression of genes in the sweet orange tree. We characterized the expression of genes in trees infected with these pathogens. Hundreds of genes were affected by the pathogens and were components of a wide range of biological pathways. The number and type of genes affected by infection reflected the complexity of symptoms caused by the pathogens. Overall the pattern of gene expression was more similar between the severe CTV and HLB than between the severe and mild strain of the same virus. Natural plant defense mechanisms were activated in response to all three pathogens, but the details varied considerably. Our results will be used by researchers interested in the response of plants to bacterial and viral diseases and in particular to researchers working on HLB and citrus tristeza disease.

Technical Abstract: Huanglongbing (HLB) and tristeza, are diseases of citrus caused by a member of the a-proteobacteria, ‘Candidatus Liberibacter asiaticus’ (CaLas), and Citrus tristeza virus (CTV) respectively. HLB is a devastating disease, but CTV strains vary from very severe to very mild. Both CaLas and CTV are phloem-restricted. The CaLas-B232 strain causes a wide range of symptoms, many of which are shared with the severe strain of CTV-B6. The mild strain CTV-B2 doesn’t induce symptoms or damage to plants. A comparison of transcriptome profiles of Citrus sinensis infected with the three pathogens might reveal host genes whose expression is affected by the presence of a pathogen in the phloem, and host genes whose expression leads to induction of symptoms in the plant. Three transcriptome profiles of ‘Valencia’ sweet orange were obtained through RNA-seq and revealed 611, 404 and 285 differentially expressed transcripts (DETs) after infection with CaLas-B232, CTV-B6 and CTV-B2 respectively. These DETs were components of a wide range of pathways involved with circadian rhythm, cell wall modification and cell organization, as well as transcription factors, transporters, hormone response and secondary metabolism, signaling and stress response. The number of DETs in response to CTV-B6 and CaLas-B232 was approximately 4 times the number of DETs in response to the two strains of CTV or CTV-B2 and CaLas-B232. A total of 38 genes were assayed by RT-qPCR and the correlation coefficients between Gfold and RT-qPCR were 0.82, 0.69, 0.81 for sweet orange plants infected with CTV-B2, CTV-B6 and CaLas-B232, respectively. The number and composition of DETs reflected the complexity of symptoms caused by the pathogens. Gene Ontology (GO) revealed greater similarities between the sweet orange response to CTV-B6 and CaLas-B232 than between the two CTV strains or between CTV-B2 and CaLas-B232, reflecting the similar physiological changes caused by both CTV-B6 and CaLas-B232. The circadian rhythm system of plants was perturbed by all three pathogens, especially by CTV-B6, and the ion balance was also disrupted by all three pathogens, especially by CaLas-B232. Defense responses related to cell wall modification, transcriptional regulation, hormones, secondary metabolites, kinases and stress were activated by all three pathogens but with different patterns.