A Novel Motif in Geminivirus Replication Proteins Interacts with the Plant Retinoblastoma-Related Protein

The geminivirus replication factor AL1 interacts with the plant retinoblastoma-related protein (pRBR) to modulate host gene expression. The AL1 protein of tomato golden mosaic virus (TGMV) binds to pRBR through an 80-amino-acid region that contains two highly predicted α-helices designated 3 and 4. Earlier studies suggested that the helix 4 motif, whose amino acid sequence is strongly conserved across geminivirus replication proteins, plays a role in pRBR binding. We generated a series of alanine substitutions across helix 4 of TGMV AL1 and examined their impact on pRBR binding using yeast two-hybrid assays. These experiments showed that several helix 4 residues are essential for efficient pRBR binding, with a critical residue being a leucine at position 148 in the middle of the motif. Various amino acid substitutions at leucine-148 indicated that both structural and side chain components contribute to pRBR binding. The replication proteins of the geminiviruses tomato yellow leaf curl virus and cabbage leaf curl virus (CaLCuV) also bound to pRBR in yeast dihybrid assays. Mutation of the leucine residue in helix 4 of CaLCuV AL1 reduced binding. Together, these results suggest that helix 4 and the conserved leucine residue are part of a pRBR-binding interface in begomovirus replication proteins

Diverse circular replication-associated protein encoding viruses circulating in invertebrates within a lake ecosystem

International audienceOver the last five years next-generation sequencing has become a cost effective and efficient method for identifying known and unknown microorganisms. Access to this technique has dramatically changed the field of virology, enabling a wide range of environmental viral metagenome studies to be undertaken of organisms and environmental samples from polar to tropical regions. These studies have led to the discovery of hundreds of highly divergent single stranded DNA (ssDNA) virus-like sequences encoding replication-associated proteins. Yet, few studies have explored how viruses might be shared in an ecosystem through feeding relationships. Here we identify 169 circular molecules (160 CRESS DNA molecules, nine circular molecules) recovered from a New Zealand freshwater lake, that we have tentatively classified into 51 putatively novel species and five previously described species (DflaCV-3, -5, -6, -8, -10). The CRESS DNA viruses identified in this study were recovered from molluscs (Echyridella menzeisii, Musculium novaezelandiae, Potamopyrgus antipodarum and Physella acuta) and insect larvae (Procordulia grayi, Xanthocnemis zealandica, and Chironomus zealandicus) collected from Lake Sarah, as well as from the lake water and benthic sediments. Extensive diversity was observed across most CRESS DNA molecules recovered. The putative capsid protein of one viral species was found to be most similar to those of members of the Tombusviridae family, thus expanding the number of known RNA-DNA hybrid viruses in nature. We noted a strong association between the CRESS DNA viruses and circular molecules identified in the water and browser organisms (C. zealandicus, P. antipodarum and P. acuta), and between water sediments and undefended prey species (C. zealandicus). However, we were unable to find any significant correlation of viral assemblages to the potential feeding relationships of the host aquatic invertebrates. (C) 2016 Elsevier B.V. All rights reserved