Citrus leprosis: a model for the study of the plant/mite/virus interaction

Author(s)

Gabriella Dias Arena

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2018-08-31

Examining board members

Marcos Antonio Machado; Ivan de Godoy Maia; Renato Vicentini; Ricardo Harakava; Antonio Vargas de Oliveira Figueira

• Advisor: Pedro Luis Ramos González; Marcos Antonio Machado

Abstract

Citrus leprosis is caused by citrus leprosis virus C (CiLV-C), transmitted by Brevipalpus yothersi mites, and is the main viral disease of citrus in Brazil. Differently from other plant viruses, CiLV-C is unable to accomplish systemic infection in its hosts, remaining restricted to cells around the inoculation sites, where symptoms of viral infection develop. Phenotypically, these features resemble the outcome a hypersensitivity response (HR). In this study, we attempted to unravel the molecular mechanisms involved in the plant/CiLV-C/B. yothersi interaction, which are still poorly understood. To disentangle the plant/mite interaction, we analyzed the Arabidopsis thaliana transcriptome in response to B. yothersi by RNA-Seq, the levels of salicylic acid (SA) and jasmonic acid (JA) in infested plants by LC-MS/MS, and the role of the hormonal pathways during mite infestation using Arabidopsis mutant plants. Infested wild type plants induced both SA e JA pathways, whilst processes involved in plant growth and defense were repressed. sid2 e npr1 mutant plants reduced the oviposition of mites, suggesting that B. yothersi manipulate plant response to render it more susceptible to its colonization. To uncover plant/virus interaction, we identified the main events of viral replication by quantifying the CiLV-C RNA1/p29sgRNA ratio during the infection, the transcriptional Arabidopsis response to CiLV-C using RNA-Seq, the presence of dead cells and reactive oxygen species (ROS) in infected tissues through histochemical assays, and the elicitor activity of viral proteins by transient expression in Nicotiana benthamiana. Plants responded to CiLV-C with a ROS burst and the induction of genes related to cell growth, SA pathway, cell death and HR. Conversely, infected plants repressed the SA pathway and the primary metabolism. The expression of the P61 viral protein mimicked responses observed during CiLV-C infection, indicating P61 as a viral component that elicits the plant immune system. CiLV-C presence favored mite ovoposition in virus-infected leaves, suggesting that the virus benefit mite infestation. Finally, the expression of selected genes modulated during the interaction with Arabidopsis was confirmed in sweet orange (Citrus sinensis), validating the use of this model plant in the study of citrus leprosis. We also showed that other Brevipalpus-transmitted viruses (BTVs) infect Arabidopsis, which thus can be used as an alternative host in the studies of plant interaction with CiLV-C-phylogenetically distant BTVs. The results presented here provided a better understanding of the processes developed during citrus leprosis disease and will be helpful to the establishment of sustainable strategies of the disease control (AU)

• FAPESP's process: 14/00366-8 - Arabidopsis thaliana e Citrus leprosis virus-C: a model for the plant-pathogen interaction study
• Grantee: Gabriella Dias Arena
• Support Opportunities: Scholarships in Brazil - Doctorate