Mungbean yellow mosaic Indian virus encoded AC2 protein suppresses RNA silencing by inhibiting Arabidopsis RDR6 and AGO1 activities

Abstract

RNA silencing refers to a conserved RNA-directed gene regulatory mechanism in a wide range of eukaryotes. It plays an important role in many processes including growth, development, genome stability, and antiviral defense in the plants. Geminivirus encoded AC2 is identified as an RNA silencing suppressor protein, however, the mechanism of action has not been characterized. In this paper, we elucidate another mechanism of AC2-mediated suppression activity of Mungbean Yellow Mosaic India Virus (MYMIV). The AC2 protein, unlike many other suppressors, does not bind to siRNA or dsRNA species and its suppression activity is mediated through interaction with key components of the RNA silencing pathway, viz., RDR6 and AGO1. AC2 interaction inhibits the RDR6 activity, an essential component of siRNA and tasi-RNA biogenesis and AGO1, the major slicing factor of RISC. Thus the study identifies dual sites of MYMIV-AC2 interference and probably accounts for its strong RNA silencing suppression activity.

Maintenance of Cotton Leaf Curl Multan Betasatellite by Tomato Leaf Curl New Delhi Virus—Analysis by Mutation

“…TrAP performs multiple functions. It may act as a transcription factor to up-regulate expression of late (virion-sense) genes (Sunter and Bisaro, 1991 ; Gopal et al, 2007 ), modulates host gene expression including micro RNA genes (Trinks et al, 2005 ; Amin et al, 2011a ), can be a pathogenicity factor (Van Wezel et al, 2001 ; Matić et al, 2016 ), a suppressor of transcriptional and post-transcriptional gene silencing (van Wezel et al, 2003 ; Buchmann et al, 2009 ; Jackel et al, 2015 ; Kumar et al, 2015 ), may delay virus infection (Shen et al, 2014 ; Krenz et al, 2015 ), may counter programmed cell death (Hussain et al, 2007 ; Mubin et al, 2010 ), conditions a virus non-specific enhanced-susceptibility phenotype (Sunter et al, 2001 ), suppresses jasmonate-mediated defense (Rosas-Díaz et al, 2016 ), and inactivates the SNF1-related kinase by interacting with it and adenosine kinase (Hao et al, 2003 ). Clearly TrAP is an important protein for ToLCNDV being involved in control of gene expression and numerous interactions with the host plant.…”

“…The DNA A of bipartite and genomes of monopartite begomoviruses encode on the virion-sense strand the (A)V2 protein [involved in movement of the virus in plants (Rojas et al, 2001 )] and the coat protein (CP; involved in in planta movement, and insect transmission between plants; Rojas et al, 2005 ). The complementary-sense strand encodes the replication-associated protein [Rep; the only virus-encoded protein required for replication of the virus genome, a rolling circle replication (RCR) initiator protein, as well as a suppressor of transcriptional gene silencing (TGS) Hanley-Bowdoin et al, 2004 ; Rodríguez-Negrete et al, 2013 ], the transcriptional-activator protein [TrAP; which up-regulates the late, virion-sense genes (Sunter and Bisaro, 1997 ), modulates host gene expression (Hao et al, 2003 ; Wang et al, 2003 ; Buchmann et al, 2009 ; Baliji et al, 2010 ; Castillo-González et al, 2015 ; Kumar et al, 2015 ), overcomes virus induced hypersensitive cell death (Hussain et al, 2007 ; Mubin et al, 2010 ), and is a suppressor of host defense mediated by PTGS (Yang et al, 2007 )], the replication-enhancer protein (REn; helps in establishing a favorable environment for virus replication; Settlage et al, 2005 ) and the C4 protein (a suppressor of PTGS and pathogenicity determinant; Vanitharani et al, 2004 ; Gopal et al, 2007 ; Saeed et al, 2008 ). The proteins encoded on the DNA B component [the virion-sense encoded nuclear shuttle protein (NSP) and the complementary-sense encoded movement protein (MP)] are involved in cell-to-cell and long-distance movement of the virus (Noueiry et al, 1994 ).…”

Alfalfa dwarf cytorhabdovirus P protein is a local and systemic RNA silencing supressor which inhibits programmed RISC activity and prevents transitive amplification of RNA silencing

“…Targeting of AGO proteins by RSS has been shown to cause inhibition of slicer activity (Azevedo et al, 2010;Fernández-Calvino et al, 2016;Giner et al, 2010;Kumar et al, 2015;Mann et al, 2016a;Zhang et al, 2006). We hypothesized that ADV P may also interact with AGO1 and/or AGO4 to disrupt slicer activity of assembled RISC complexes.…”

“…However, other RSS function by interacting with host proteins that are either important components of the silencing machinery or proposed regulators of the silencing pathway (Kong et al, 2014). This includes RSS that interact with AGO1 to block siRNA loading, inhibit slicing activity, or inhibit translational repression (Azevedo et al, 2010;Chiu et al, 2010;Csorba et al, 2010;Feng et al, 2013;Giner et al, 2010;Karran and Sanfacon, 2014;Kumar et al, 2015;Mann et al, 2016a;Zhang et al, 2006). In addition, tobacco rattle virus 16K and CMV 2b proteins interact with AGO4 to block RISC assembly and both in vitro slicing activity and RNA-directed DNA methylation, respectively (Fernández-Calvino et al, 2016;Hamera et al, 2012).…”

The C2 protein of tomato leaf curl Taiwan virus is a pathogenicity determinant that interferes with expression of host genes encoding chromomethylases

“…For example, African cassava mosaic virus (ACMV) AC2 can suppress established PTGS (Voinnet et al ). Mung bean yellow mosaic Indian virus (MYMIV) AC2 protein suppresses RNA silencing by inhibiting RDR6 and AGO1 activities in Arabidopsis (Kumar et al ). C2 was also found to be able to suppress transcriptional gene silencing (TGS).…”