RESUMEN
Symbiotic viruses exist in many insects; however, their functions in host insects are not well understood. In this study, we explored the role of acyrthosiphon pisum virus (APV) in the interaction of its host aphid Acyrthosiphon pisum with plants. APV is primarily located in aphid salivary glands and gut and propagated in the insect. APV is horizontally transmitted to host plants during aphid feeding, but the virus does not replicate in the host plant. When the pea host race of aphids colonized two low-fitness plants, Medicago truncatula and Vicia villosa, the virus titers in both the aphids and plants significantly increased. Furthermore, APV infection strongly promoted the survival rate of the pea host race on V. villosa. Transcriptomic analysis showed that only 0.85% of aphid genes responded to APV infection when aphids fed on V. villosa, with a fold change in transcript levels of no more than fourfold. The improved survival due to APV infection was apparently related to the inhibitory effect of the virus on levels of phytohormone jasmonic acid (JA) and JA-isoleucine. Our data suggest a benefit of the symbiotic virus to its aphid host and demonstrate a novel case of symbiotic virus-mediated three-species interaction.
Asunto(s)
Áfidos , Ciclopentanos , Oxilipinas , Virus ARN , Simbiosis , Animales , Áfidos/virología , Ciclopentanos/metabolismo , Interacciones Huésped-Patógeno , Medicago truncatula/parasitología , Medicago truncatula/virología , Oxilipinas/metabolismo , Pisum sativum/parasitología , Pisum sativum/virología , Plantas/parasitología , Plantas/virología , Virus ARN/fisiología , Vicia/parasitología , Vicia/virologíaRESUMEN
Virus infections induce the expression of ARGONAUTE1 (AGO1) mRNA and in parallel enhance the accumulation of miR168 (regulator of AGO1 mRNA). Here, we show that in virus-infected plants the enhanced expression of AGO1 mRNA is not accompanied by increased AGO1 protein accumulation. We also show that the induction of AGO1 mRNA level is a part of the host defence reaction, whereas the induction of miR168, which overlaps spatially with virus-occupied sectors, is mediated mainly by the Tombusvirus p19 RNA-silencing suppressor. The absence of p19 results in the elimination of miR168 induction and accompanied with the enhanced accumulation of AGO1 protein. In transient expression study, p19 mediates the induction of miR168 and the down-regulation of endogenous AGO1 level. P19 is not able to efficiently bind miR168 in virus-infected plants, indicating that this activity is uncoupled from the small RNA-binding capacity of p19. Our results imply that plant viruses can inhibit the translational capacity of AGO1 mRNA by modulating the endogenous miR168 level to alleviate the anti-viral function of AGO1 protein.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Regulación de la Expresión Génica de las Plantas , MicroARNs/metabolismo , ARN Mensajero/metabolismo , ARN de Planta/metabolismo , Tombusvirus/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Arabidopsis/virología , Proteínas de Arabidopsis/genética , Proteínas Argonautas , Regulación hacia Abajo , Solanum lycopersicum/genética , Solanum lycopersicum/metabolismo , Solanum lycopersicum/virología , Medicago truncatula/genética , Medicago truncatula/metabolismo , Medicago truncatula/virología , MicroARNs/genética , Plantas Modificadas Genéticamente/genética , Plantas Modificadas Genéticamente/metabolismo , ARN Mensajero/genética , ARN de Planta/genética , ARN Interferente Pequeño/genética , ARN Interferente Pequeño/metabolismo , Nicotiana/genética , Nicotiana/metabolismo , Nicotiana/virología , Tombusvirus/genéticaRESUMEN
Virus-induced gene silencing (VIGS) has become an important reverse genetics tool for functional genomics. VIGS vectors based on Pea early browning virus (PEBV, genus Tobravirus) and Bean pod mottle virus (genus Comovirus) are available for the legume species Pisum sativum and Glycine max, respectively. With the aim of extending the application of the PEBV VIGS vector to other legumes, we examined susceptibility of 99 accessions representing 24 legume species including 21 accessions of Medicago truncatula and 38 accessions Lotus japonicus. Infectivity of PEBV was tested by agro-inoculation with a vector carrying the complete beta-glucuronidase (GUS) coding sequence. In situ histochemical staining analysis indicated that 4 of 21 M. truncatula and three of three Lathyrus odorata accessions were infected systemically by GUS tagged PEBV, while none of 38 L. japonicus accessions displayed GUS staining of either inoculated or uninoculated leaves. Agro-inoculation of plants representing PEBV-GUS susceptible M. truncatula and L. odorata accessions with PEBV carrying a fragment of Phytoene desaturase (PDS) resulted in development of a bleaching phenotype suggesting a down-regulation of PDS expression. In M. truncatula this was supported by quantification of PDS mRNA levels by real-time PCR.