Molecular basis of the interactions between luteoviruses and aphids

International audienc

The use of molecular beacons combined with NASBA for the sensitive detection of Sugarcane yellow leaf virus

Sugarcane yellow leaf virus (ScYLV) is widely distributed in Brazil and other sugarcane producing countries causing significant yield losses. Due to the high incidence of the aphid vector, the virus is widespread in the field and in parental clones used in sugarcane breeding programmes. Aiming to present a sensitive and reliable detection of ScYLV, we have adapted an AmpliDet RNA system, compared it with the currently available detection methods and discussed its applicability for routine diagnosis. AmpliDet RNA consists of nucleic acid sequence-based amplification (NASBA) of the target RNA with specific primers and simultaneous real-time detection of the amplification products with molecular beacons. The results showed that the system produced a detection level of at least 100 fg of purified virus. Virus was readily detected in plant tissues with low levels of infection (without the need of previous RNA extraction) and in the hemolymph of aphids. The method showed to be virus-specific, testing negative for other species of the Luteoviridae. In conclusion, the system has potential to become a diagnostic method for the detection of sugarcane viruses.108540140

Molecular bases of the interactions between luteoviruses and aphids *

Many viruses infecting vertebrates or plants are transmitted by arthropod vectors in a circulative manner. This requires the virus to cross epithelial cells of the gut and salivary glands, and to resist the potentially hostile environment of the vector. Fundamental knowledge regarding the strategies adopted by these persistent viruses to overcome the transmission barriers mentioned is surprisingly meagre. Here we describe the involvement of endosymbiotic bacteria in the transmission of potato leafroll virus by its aphid vector Myzus persicae. Symbionin, the major protein synthesized and released into the haemolymph by the bacterial endosymbiont, was found to determine the persistent nature of the luteovirus in its vector. The virus displays a strong affinity to this protein (Mr = 63 000) which has high homology with the Escherichia coli heat shock protein groEL. The absence of symbionin in the haemolymph of aphids treated with antibiotics leads to rapid degradation of the major capsid protein of the virus and concomitant loss of infectivity.Étude moléculaire des interactions entre les lutéovirus et les aphides. La plupart des virus de vertébrés et des virus de plantes sont transmis par des vecteurs arthropodes, selon un mode circulant. Ceci implique le passage des particules virales au travers des cellules épithéliales de l'intestin et de celles des glandes salivaires, ainsi que la résistance des particules virales à l'environnement potentiellement hostile du vecteur. Les stratégies adoptées par ces virus persistants afin de passer les barrières de transmission mentionnées ci-dessus sont peu connues. Nous décrivons ici le rôle d'une bactérie endosymbiotique au cours de la transmission du virus de l'enroulement de la pomme de terre par son vecteur qui est un aphide, Myzus persicae. Il a été montré que la symbionine, une protéine synthétisée de manière prédominante par la bactérie endosymbiotique de l'aphide et libérée dans l'hémolymphe de celui-ci, détermine la nature persistante du virus dans son vecteur. Le virus montre une forte affinité pour la symbionine (M, 63K), qui possède de fortes homologies de séquence avec la protéine «heat-shock» groEL d'Escherichia coli. L'absence de symbionine dans l'hémolymphe d'aphides traités par des antibiotiques conduit à une rapide dégradation des particules virales et de leur pouvoir infectieux

Ocorrência de vírus em batata em sete estados do Brasil Virus occurrence in potatoes in seven Brazilian States

As viroses causam rápida degenerescência dos tubérculos-sementes de batata. Em condições tropicais, em que a presença de afídeos vetores é constante e a estrutura das populações de vírus é dinâmica, a pressão das doenças é enorme. Conhecer essa dinâmica é uma ferramenta importante para a sustentabilidade da produção de batata. Realizou-se um levantamento abrangente da ocorrência de viroses em batata no Brasil, além de estudar-se a distribuição das estirpes de Potato virus Y (PVY) associadas ao mosaico da batata. Em 2005 e 2006 foram visitadas lavouras em sete estados brasileiros, coletando-se folíolos com sintomas de viroses (1.256 amostras) e amostras aleatórias (360 amostras). Foi feita também uma estimativa visual da incidência de mosaico e enrolamento-das-folhas em vários dos campos visitados. Das 1.256 amostras suspeitas, 840 apresentaram reação positiva em teste sorológico para PVY (66,9%), 128 para Potato leaf roll virus (PLRV) (10,2%), 79 para Potato virus S (PVS) (6,3%) e nenhuma para Potato virus X (PVX). Os resultados dos testes de detecção por DAS-ELISA, biológico e RT-PCR mostraram a presença quase absoluta do subgrupo necrótico de PVY, em sua maioria PVY NTN. A análise de uma sub-amostragem em todos os municípios visitados confirmou que essa variante está hoje presente nos sete estados visitados. Amostras de PVY NTN foram obtidas das cultivares Asterix, Atlantic, Agata, Achat, Baronesa, Baraka, Bintje, Caesar, Cupido, Marijke, Monalisa, Panda e Vivaldi, que apresentaram diferentes níveis de suscetibilidade. As amostras aleatórias revelaram um quadro muito similar ao encontrado com as amostras sintomáticas. PLRV foi identificado em MG, BA, PR e SC, em várias lavouras de forma muito freqüente. PVS foi identificado nesses mesmos estados e também em SP. PVX foi detectado em apenas uma amostra tomada ao acaso em Serra do Salitre (MG). O contraste entre a avaliação visual dos sintomas e os resultados do teste de detecção por ELISA revelou a possibilidade de infecção latente por PVY em níveis relevantes na cultivar Asterix.<br>Viruses are responsible for the quick degeneration of potato seed-tubers. In the tropics, where aphid vectors are constantly present and the structure of virus populations is dynamic, the disease pressure is enormous. Therefore, the knowledge of such dynamics is definitely an extremely valuable tool towards the sustainability of the national potato production. In this study, we report a broad survey of virus occurrence in potato, in Brazil. In addition, we studied the distribution of the Potato virus Y (PVY) strains associated with mosaic symptoms on potatoes. In 2005 and 2006, we visited potato fields in seven Brazilian States. We collected leaves of symptomatic plants (1,256 samples) and also at random (360 samples). In addition, in several fields a visual assessment was carried out to estimate mosaic and leafroll incidence. From the 1,256 samples with symptoms, 840 tested serologically were positive to PVY (66.9%), 128 to PLRV (10.2%), 79 to PVS (6.3%), and none to PVX. Serology using DAS-ELISA and also biological and RT-PCR tests revealed an almost exclusive occurrence of the PVY necrotic strain, predominantly the necrotic subgroup PVY NTN. The analysis of a sub-sample representing all surveyed Counties indicated that the necrotic strain was universally present. Cultivars Asterix, Atlantic, Agata, Achat, Baronesa, Baraka, Bintje, Caesar, Cupido, Marijke, Monalisa, Panda, and Vivaldi, although displaying different susceptibility levels, were all infected by PVY NTN. The analysis of leaves collected at random showed similar results. PLRV was identified in four States (Minas Gerais, Bahia, Paraná, and Santa Catarina), while PVS was present in the State of São Paulo as well. PVX was found in only one sample collected at random in Serra do Salitre, State of Minas Gerais. The contrast between visual evaluation and the results of the detection test by ELISA strongly indicated the presence of a relevant rate of PVY latent infection on cultivar Asterix

Virus-vector relationship in the Citrus leprosis pathosystem

Citrus leprosis has been one of the most destructive diseases of citrus in the Americas. In the last decade important progress has been achieved such as the complete genome sequencing of its main causal agent, Citrus leprosis virus C (CiLV-C), belonging to a new genus Cilevirus. It is transmitted by Brevipalpus yothersi Baker (Acari: Tenuipalpidae), and is characterized by the localized symptoms it induces on the leaves, fruits and stems. It occurs in the American continents from Mexico to Argentina. The virus was until recently considered restricted to Citrus spp. However, it was found naturally infecting other plants species as Swinglea glutinosa Merrill and Commelina benghalensis L., and has been experimentally transmitted by B. yothersi to a large number of plant species. Despite these advances little is known about the virus-vector relationship that is a key to understanding the epidemiology of the disease. Some components of the CiLV-C/B. yothersi relationship were determined using the common bean (Phaseolus vulgaris L. cv. ‘IAC Una’) as a test plant. They included: (a) the virus acquisition access period was 4 h; (b) the virus inoculation access period was 2 h; (c) the latent period between acquisition and inoculation was 7 h; (d) the period of retention of the virus by a single viruliferous mite was at least 12 days; (d) the percentage of viruliferous individuals from mite colonies on infected tissues ranged from 25 to 60%. The experiments confirmed previous data that all developmental stages of B. yothersi (larva, protonymph and deutonymph, adult female and male) were able to transmit CiLV-C and that transovarial transmission of the virus did not occur. CiLV-C can be acquired from lesions on leaves, fruits and stems by B. yothersi. Based on the distribution of lesions produced by single viruliferous B. yothersi on bean leaves, it is concluded that they tend to feed in restricted areas, usually near the veins. The short latent and transmission periods during the larval stage suggest that the CiLV-C/B. yothersi relationship is of the persistent circulative type.Fundación de apoyo a la investigación estatal/[2014/08458-9]/Fapesp/BrasilConsejo Nacional de desarrollo científico y tecnológico/[47.2425/2013-7]/CNPq/BrasilFundación de apoyo a la investigación estatal/[2008/57477-5]/Fapesp/BrasilFundación de apoyo a la investigación estatal/[2013/25713-0]/Fapesp/BrasilUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Biología Celular y Molecular (CIBCM