RESUMO
Citrus huanglongbing (HLB) is a devastating disease associated with Candidatus Liberibacter asiaticus spp. (CLas), a bacterium restricted to the sieve tube system of the phloem that is transmitted by the psyllid vector, Diaphorina citri. In this study, the human antimicrobial peptides, lysozyme and ß-defensin 2, were targeted to the vascular tissue of Mexican lime (Citrus x aurantifolia [Christm.] Swingle) by fusion to a phloem-restricted protein. Localized expression was achieved, via Agrobacterium tumefaciens-mediated transformation of the stem, which led to protein expression and mobilization within the vascular tissue of heterotrophic tissues. HLB-infected plants were monitored for 360 days. Lower bacteria titers were observed in plants expressing either ß-defensin 2, lysozyme, or the combination thereof, and these plants had increased photosynthesis, compared to untreated control trees. Thus, targeting of antimicrobial proteins to the vascular tissue was effective in decreasing CLas titer, and alleviating citrus greening symptoms. Based on these findings, this strategy could be used to effectively treat plants that are already infected with bacterial pathogens that reside in the phloem translocation stream.
Assuntos
Citrus , Defensinas , Muramidase , Doenças das Plantas/prevenção & controle , Proteínas de Plantas , Rhizobiaceae , Agrobacterium/genética , Citrus/genética , Citrus/metabolismo , Citrus/microbiologia , Defensinas/genética , Defensinas/farmacologia , Muramidase/genética , Muramidase/farmacologia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Proteínas de Plantas/farmacologia , Proteínas Recombinantes de Fusão/farmacologiaRESUMO
BACKGROUND: The bacterial disease citrus huanglongbing (HLB), associated with "Candidatus Liberibacter asiaticus" (C.Las) has severely impacted the citrus industry, causing a significant reduction in production and fruit quality. In the present study, it was monitored the C.Las population dynamics in symptomatic, HLB-positive Mexican lime trees (Citrus aurantifolia Swingle) in a tropical, citrus-producing area of Mexico. The objective of this study was to identify the dynamics of the population of huanglongbing-associated bacterium Candidatus Liberibacter asiaticus and its insect vector in Citrus aurantifolia Swingle (Mexican lime). MATERIALS AND METHODS: Leaf samples were collected every 2 months over a period of 26 months for quantification of bacterial titers and young and mature leaves were collected in each season to determine preferential sites of bacterial accumulation. The proportion of living and dead bacterial cells could be determined through the use of quantitative real-time PCR in the presence of ethidium monoazide (EMA-qPCR). RESULTS: It was observed a lower bacterial titer at high temperatures in the infected trees relative to titers in mild weather, despite a higher accumulation of the insect vector Diaphorina citri in these conditions. This study also revealed seasonal fluctuations in the titers of bacteria in mature leaves when compared to young leaves. No statistically significant correlation between any meteorological variable, C.Las concentration and D. citri population could be drawn. CONCLUSION: Although, HLB management strategies have focused on vector control, host tree phenology may be important. The evaluation of citrus phenology, C.Las concentration, ACP population and environmental conditions provides insights into the cyclical, seasonal variations of both the HLB pathogen and its vector. These findings should help in the design of integrative HLB control strategies that take into account the accumulation of the pathogen and the presence of its vector.
Assuntos
Citrus aurantiifolia/microbiologia , Produtos Agrícolas/microbiologia , Doenças das Plantas/microbiologia , Folhas de Planta/microbiologia , Rhizobiaceae/crescimento & desenvolvimento , Árvores/microbiologia , Animais , Carga Bacteriana , Citrus aurantiifolia/crescimento & desenvolvimento , Produtos Agrícolas/crescimento & desenvolvimento , Vetores de Doenças , Hemípteros/microbiologia , Interações Hospedeiro-Patógeno , México , Viabilidade Microbiana , Folhas de Planta/crescimento & desenvolvimento , Dinâmica Populacional , Rhizobiaceae/genética , Estações do Ano , Fatores de Tempo , Árvores/crescimento & desenvolvimento , Tempo (Meteorologia)RESUMO
The causal agents of Citrus leprosis are viruses; however, extant diagnostic methods to identify them have failed to detect known viruses in orange, mandarin, lime and bitter orange trees with severe leprosis symptoms in Mexico, an important citrus producer. Using high throughput sequencing, a virus associated with citrus leprosis was identified, belonging to the proposed Dichorhavirus genus. The virus was termed Citrus Necrotic Spot Virus (CNSV) and contains two negative-strand RNA components; virions accumulate in the cytoplasm and are associated with plasmodesmata-channels interconnecting neighboring cells-suggesting a mode of spread within the plant. The present study provides insights into the nature of this pathogen and the corresponding plant response, which is likely similar to other pathogens that do not spread systemically in plants.