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Master's Dissertation
DOI
https://doi.org/10.11606/D.11.2014.tde-16062014-094145
Document
Author
Full name
Luciane Fender Coerini
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
Piracicaba, 2014
Supervisor
Committee
Astúa, Juliana de Freitas (President)
Breton, Michèle Claire
Vitorello, Claudia Barros Monteiro
Title in Portuguese
Expressão de genes das vias de jasmonato e etileno na resposta de plantas de citros às bactérias Candidatus Liberibacter spp., causadoras do Huanglongbing
Keywords in Portuguese
Citrus sp.
Poncirus sp.
Expressão diferencial de genes
HLB
Interação planta-patógeno
Resposta a patógenos
Transcriptoma
Abstract in Portuguese
A citricultura destaca-se dentro do agronegócio brasileiro gerando dividendos diretos com exportações e empregos, e indiretos com arrecadação de impostos. No entanto, ainda padece com problemas fitossanitários, com destaque para o HLB (Huanglongbing, HLB, ex-greening), que nos últimos dez anos tem dizimado pomares e provocado o abandono da cultura por muitos produtores. Causada no Brasil pelas bactérias Candidatus Liberibacter asiaticus e Ca. Liberibacter americanus, é uma doença sistêmica, restrita aos vasos do floema, e induz ao aparecimento de sintomas semelhantes àqueles causados por deficiência de nutrientes em folhas e ramos, frutos com tamanhos reduzidos e assimétricos e coloração amarelada das plantas, tornando-as economicamente inviáveis. A transmissão da doença acontece naturalmente pelo inseto Diaphorina citri, e artificialmente por meio de borbulhas contaminadas. Todas as variedades de citros e rutáceas próximas são comprovadamente suscetíveis ao HLB; entretanto, há diferenças marcantes entre níveis de suscetibilidade entre os genótipos, como Poncirus trifoliata, que apresenta certa resistência ou tolerância à doença. Os mecanismos de patogenicidade de Ca. Liberibacter spp. e a resposta molecular da planta à infecção ainda não estão bem definidos e o estudo da ativação dos mecanismos de defesa da planta induzidos por hormônios vegetais é um importante foco na elucidação deste complexo patossistema. Diante deste panorama, este estudo propôs avaliar o perfil de expressão de genes associados às vias do jasmonato e do etileno em plantas de Citrus sinensis L. Osb. (suscetível) e Poncirus trifoliata (L.) Raf. (resistente ou tolerante) em resposta à infecção pelas duas espécies de bactérias causadoras do HLB no Brasil, separadamente. Os perfis transcricionais dos genes avaliados não foram estatisticamente distintos, mas mereceram destaque os genes de biossíntese e metabolismo de jasmonato LOX2, AOC3 e JMT, os genes sinalizadores da via de jasmonato JAZ2 e MYC2, o gene de biossíntese de etileno SAM1, os receptores de etileno ETR1, ERS1 e EIN4, o regulador negativo de etileno CTR1, o regulador positivo da sinalização de etileno EIN2, os fatores de transcrição EIN3, EIL1, ERF1, ERF2, ERF/AP2, uma MAPkinase MAPK6 e uma proteína PR PR-4. Estes resultados mostram que as vias sinalizadas por jasmonato e etileno são modificadas pelas bactérias Ca. Liberibacter spp. No entanto, não foi possível comprovar a importância destas vias na resposta diferencial de genótipos suscetível e resistente/ tolerante de citros ao HLB.
Title in English
Expression of genes of the jasmonate and ethylene pathways in the response of citrus plants to Candidatus Liberibacter spp., the causal agents of Huanglongbing
Keywords in English
Citrus sp.
Poncirus sp.
Differential gene expression: Transcriptome
HLB
Plant-pathogen interaction
Response to pathogens
Abstract in English
The citrus industry stands out in the Brazilian agribusiness generating direct and indirect jobs and significant revenues. However, the citrus crop faces several diseases, especially the HLB (Huanglongbing, ex-greening), which, in the last ten years, have caused severe losses to growers. In Brazil, HLB is caused by the bacteria Candidatus Liberibacter asiaticus and Ca. Liberibacter americanus, which are restricted to the phloem and induce symptoms similar to those caused by nutrient deficiency in citrus leaves and branches. Fruits are of reduced size and asymmetrical, and the plants tend to show overall yellowing. These symptoms altogether lead to the economical death of the plant. Transmission of the pathogens occurs naturally by the Asian citrus psyllid Diaphorina citri, or by contaminated buds. All citrus varieties and relatives are considered susceptible to HLB; however, there are clear differences in levels of susceptibility among genotypes. Poncirus trifoliata, for instance, exhibits some resistance or tolerance to the disease. The mechanisms involved in the pathogenesis of Ca. Liberibacter spp. and the molecular responses of the hosts to the infection are still unknown, but emphasis has been given to the defense mechanisms induced by plant hormones in order to try to elucidate the interactions of such complex pathosystem. Based on this scenario, this study aimed to evaluate the expression profile of Citrus sinensis (L.) Osb. (susceptible) and Poncirus trifoliata (L.) Raf. (resistant or tolerant) genes associated with the jasmonate and ethylene pathways in response to infection by both species of Ca. Liberibacter spp. causing HLB in Brazil, separately. The transcriptional profiles did not differ statistically, for the evaluated genes, including those in the jasmonate biosynthesis and metabolism (LOX2, AOC3 and JMT), signaling pathway (JAZ2 and MYC2), biosynthesis of ethylene (SAM1), ethylene receptors (ETR1, ERS1 and EIN4), negative regulator of ethylene (CTR1), positive regulator of ethylene signaling (EIN2), transcription factors (EIN3, EIL1, ERF1, ERF2, ERF/AP2), a MAPkinase (MAPK6) and a PR protein (PR-4). These results suggest that the jasmonate and ethylene pathways exhibit some modulation caused by the bacteria Ca Liberibacter spp. However, it does not seem that these pathways are relevant for the differential response of susceptibility or resistance/ tolerance of the citrus genotypes to HLB.
 
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Publishing Date
2014-07-01
 
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