Post-transcriptional gene silencing suppressor activity of two non-pathogenic alphasatellites associated with a begomovirus

Abstract

Alphasatellites and betasatellites are begomovirus-associated single-stranded circular DNA molecules. Two distinct alphasatellites, Gossypium darwinii symptomless alphasatellite and Gossypium mustelinium symptomless alphasatellite, were previously isolated from Gossypium davidsonii and G.mustelinium. Here we show that the replication-associated proteins (Rep: a rolling-circle replication initiator protein) encoded by these alphasatellites interact with the Rep and C4 proteins encoded by their helper begomovirus, Cotton leaf curl Rajasthan virus (CLCuRaV), in a yeast two-hybrid assay. Both the alphasatellite-encoded Reps were found to have strong gene silencing suppressor activity, in contrast to the betasatellite-encoded betaC1 and CLCuRaV-encoded C2, C4 and V2 proteins. The presence of alphasatellites maintained suppression of gene silencing in the youngest, actively growing tissue of CLCuRaV-betasatellite-infected plants. This is the first demonstration of a rolling-circle replication initiator protein with suppressor of gene silencing activity and provides a possible explanation for the selective advantage provided by the association of alphasatellites with begomovirus-betasatellite complexes.

Association of Satellites with a Mastrevirus in Natural Infection: Complexity of Wheat Dwarf India Virus Disease

“…Unlike betasatellites, where the ␤C1 proteins have been reported as the determinants of pathogenicity and as silencing suppressors (15)(16)(17)(18)(19)(20), the alphasatellites are believed to have a role in either attenuating viral symptoms (24,25) or in overcoming host defense (26). In contrast, in the presence of CLCuMA or GLCuA, a higher level of accumulation of WDIV was documented in this study.…”

“…Alphasatellites are also approximately half the size (ϳ1,350 bp) of their helper begomoviruses and encode a single product, which is similar to the replication-associated protein (Rep; a rolling-circle replication initiator protein) of another family of single-stranded DNA viruses, the nanoviruses (7)(8)(9). Unlike betasatellites, the presence of alphasatellites, as in the case of Ageratum yellow vein Singapore alphasatellite (AYVSGA), Tobacco curly shoot alphasatellite (TbCSA), Gossypium darwinii symptomless alphasatellite (GDarSLA), and Gossypium mustelinum symptomless alphasatellite (GMusSLA) in plants infected with begomovirus-betasatellite complexes, reduces the accumulation of betasatellite (24)(25)(26) and attenuates viral symptoms (24,25).…”

Mutational Analysis of Effectors Encoded by Monopartite Begomoviruses and Their Satellites

“…Recently, two 'DNA-1-type' alphasatellites Gossypium mustelinium symptomless alphasatellite (GMusSLA) and Gossypium darwinii symptomless alphasatellite (GDarSLA) phylogenetically divergent from the DNA-2-type alphasatellite have each been shown to attenuate symptoms caused by their helper begomovirus [60]. However [35] hypothesize that symptom attenuation and a relative reduction in betasatellite accumulation might result from DNA-2-mediated modulation of betasatellite activity.…”

“…Also alphasatellite rep can interact with C4 of CLCuRaV that might be providing an additional possible mechanism for symptom amelioration by alphasatellites. Furthermore alpha-Rep down regulate betasatellite replication (In the field), and thus downregulation of the manifestation of the pathogenicity determinant C1 [60], moreover alphaRep proteins GMusSLA and GDarSLA can act as a strong suppression of posttranscriptional gene silencing (PTGS) [60].…”

Association of a recombinant Cotton leaf curl Bangalore virus with yellow vein and leaf curl disease of okra in India

“…Alphasatellites are self-replicating circular ssDNA molecules, depend on the helper virus for movement, encapsidation and vector transmission and play no role in symptom induction [5][6][7]32]. However, recently the Rep proteins encoded by some alphasatellites have been shown to have suppressor activity of RNA silencing, suggesting that alphasatellites are involved in overcoming host defenses [36]. In the Old world, both monopartite and bipartite begomoviruses has been identified [52] however, the majority among these is monopartite viruses associated with the additional ssDNA molecules [3].The begomoviruses natives to the New world are bipartite [16,24,39].…”