Identification of an RNA-silencing suppressor in the genome of Grapevine virus A

Abstract

Higher plants use post-transcriptional gene silencing (PTGS), an RNA-degradation system, as a defence mechanism against viral infections. To counteract this, plant viruses encode and express PTGS suppressor proteins. Four of the five proteins encoded by the Grapevine virus A (GVA) genome were screened using a green fluorescent protein (GFP)-based transient expression assay, and the expression product of ORF5 (protein p10) was identified as a suppressor of silencing. ORF5 p10 suppressed local and systemic silencing induced by a transiently expressed single-stranded sense RNA. This protein was active towards both a transgene and exogenous GFP mRNAs. Ectopic expression of GVA-ORF5 by a Potato virus X vector enhanced symptom severity. The findings that p10 markedly reduces the levels of small interfering RNAs (siRNAs) and that the recombinant protein is able to bind single-stranded and double-stranded forms of siRNAs and microRNAs, suggest the existence of a potential mechanism of suppression based on RNA sequestering.

Antiviral Silencing and Suppression of Gene Silencing in Plants

“…RSV suppressor NS3 was found to bind to various RNA forms like ss-siRNA, ds-siRNA or long ssRNA (but not long dsRNA). By this, NS3 is able to suppress and revert local silencing but also prevent the long distance spread of silencing signal (Chellappan et al 2005;Xiong et al 2009;Zhou et al 2006). Similarly, Grapevine virus A (GVA) p10 suppressor was also suggested to act through both ss-and ds-si/miRNA binding (Chellappan et al 2005;Xiong et al 2009;Zhou et al 2006).…”

“…Transgenic AC4 decreases accumulation of miRNAs and up-regulates target mRNAs. AC4 acts downstream of the unwinding process by binding miRNAs presumably loaded into AGO (Chellappan et al 2005;Xiong et al 2009;Zhou et al 2006). RSV suppressor NS3 was found to bind to various RNA forms like ss-siRNA, ds-siRNA or long ssRNA (but not long dsRNA).…”

Sequence Comparison and Phylogeny of Nucleotide Sequence of Coat Protein and Nucleic Acid Binding Protein of a Distinct Isolate of Shallot virus X from India

“…Coat protein plays an important role in virus infection while NB has been shown to play a role in suppressor of RNA silencing [12]. Therefore, knowledge of sequences of CP and NB would help develop diagnostics and management strategies of ShVX.…”

Análisis Funcional De Proteínas Codificadas Por El Virus De La Rotura Del Color De La Flor Del Pelargonium

“…En algunos casos, la unión a los dúplex no tiene restricciones de tamaño y los supresores pueden unirse tanto a dsRNAs largos como a cortos. Una estrategia menos frecuente, pero igualmente efectiva, es la unión a siRNAs monocatenarios, antes o después de haberse incorporado a AGO [Zhou et al, 2006b;Xiong et al, 2009]. El bloqueo de la formación de complejos RISC activos también es posible a partir de mecanismos totalmente diferentes, como aquellos que interfieren en la metilación de los siRNAs por parte de la enzima HEN1 [Ebhardt et al, 2005;Vogler et al, 2007;Csorba et al, 2007;Lozsa et al, 2008] o los que tienen como consecuencia el corte de los dúplex en fragmentos aún más pequeños que no pueden ser incorporados a RISC [Kreuze et al, 2005;Cuellar et al, 2009].…”

“…Al igual que otros supresores relacionados o no filogenéticamente [Voinnet et al, 1999;Thomas et al, 2003;Te et al, 2005;Meng et al, 2006;Zhou et al, 2006b], la proteína p37 del PFBV es capaz de acentuar dramáticamente los síntomas de una infección viral, como se ha comprobado mediante su expresión a partir de un vector derivado de PVX. Esta intensificación de la sintomatología recuerda las interacciones sinérgicas que se establecen cuando dos virus distintos co-infectan la misma planta, una intensificación que se ha asociado con un reforzamiento de la inhibición del silenciamiento por RNA y con un aumento del título viral [Pruss et al, 1997].…”