Journey of begomovirus betasatellite molecules: from satellites to indispensable partners

Betasatellites are a group of circular, single-stranded DNA molecules that are frequently found to be associated with monopartite begomoviruses of the family Geminiviridae. Betasatellites require their helper viruses for replication, movement, and encapsidation and they are often essential for induction of typical disease symptoms. The βC1 protein encoded by betasatellites is multifunctional that participates in diverse cellular events. It interferes with several cellular processes like normal development, chloroplasts, and innate immune system of plants. Recent research has indicated βC1 protein interaction with cellular proteins and its involvement in modulation of the host’s cell cycle and symptom determination. This article focuses on the functional mechanisms of βC1 and its interactions with other viral and host proteins.

     

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

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 βC1 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.     

A betasatellite-dependent begomovirus infects ornamental rose: characterization of begomovirus infecting rose in Pakistan

The Begomovirus genus of the family Geminiviridae comprises the largest group of geminiviruses. The list of begomoviruses is continuously increasing as a result of improvement in the methods for identification. Ornamental rose plants (Rosa chinensis) with highly stunted growth and leaf curling were found in Faisalabad, Pakistan. Plants were analyzed for begomovirus infection, through rolling circle amplification and PCR methods. Based on complete genome sequence homologies with other begomoviruses, a new begomovirus species infecting the rose plants was discovered. In this paper, we propose a new species name, Rose leaf curl virus (RoLCuV), for the virus. RoLCuV showed close identity (83 %) with Tomato leaf curl Pakistan virus, while associated betasatellite showed 96 % identity with Digera arvensis yellow vein betasatellite (DiAYVB), justifying a new isolate for the betasatellite. Recombination analysis of newly identified begomovirus revealed it as a recombinant of tomato leaf curl Pakistan virus from its coat protein region. The infectious molecules for virus/satellite were prepared and inoculated through Agrobacterium tumefaciens to N. benthamiana plants. RoLCuV alone was unable to induce any level of symptoms on N. benthamiana plants, but co-inoculation with cognate betasatellite produced infection symptoms. Further investigation to understand the trans-replication ability of betasatellites revealed their flexibility to interact with Rose leaf curl virus.