Desmodium mottle virus, the first legumovirus (genus Begomovirus) from East Africa

Exploring distribution and genomic diversity of begomoviruses associated with yellow mosaic disease of legume crops from India, highlighting the dominance of mungbean yellow mosaic India virus

Yellow mosaic disease (YMD) caused by several begomoviruses is one of the major constraints of over a dozen leguminous crops worldwide, particularly in Asian and Southeast Asian countries. The present study aimed to investigate the distribution, diversity and prevalence of begomoviruses associated with YMD in leguminous hosts in five agro-climatic zones of India, to assess the extent of their geographical presence and develop location and crop-specific distribution maps. One hundred and seventy-four leguminous plant samples were tested from 32 locations in India to detect YMD-causing viruses. Additionally, publicly available data were incorporated into this study to provide a comprehensive overview of their distribution in India. This resulted in 581 reports on the DNA-A component representing 119 locations, which were also utilized to depict the distribution of YMD-causing viruses on a map of India. In this study, 117 full-length DNA-A and 103 DNA-B components were successfully characterized, representing the detected mungbean yellow mosaic India virus (MYMIV), mungbean yellow mosaic virus (MYMV), and horsegram yellow mosaic virus in the collected samples. Phylogenetic analysis of isolates of these species showed no differentiation based on location in India. Diversity indices revealed the abundance (55.9%) and dominance (0.56) of MYMIV across 119 locations. These findings hold significant implications for legume researchers, offering insights into disease prevalence and geographic distribution. Furthermore, the distribution of YMD-causing viruses in different agro-climatic zones will help researchers in developing zone-specific YMD-resistant cultivars of the legume crops and would facilitate effective disease management options.

The Role of Extensive Recombination in the Evolution of Geminiviruses

Mutation, recombination and pseudo-recombination are the major forces driving the evolution of viruses by the generation of variants upon which natural selection, genetic drift and gene flow can act to shape the genetic structure of viral populations. Recombination between related virus genomes co-infecting the same cell usually occurs via template swapping during the replication process and produces a chimeric genome. The family Geminiviridae shows the highest evolutionary success among plant virus families, and the common presence of recombination signatures in their genomes reveals a key role in their evolution. This review describes the general characteristics of members of the family Geminiviridae and associated DNA satellites, as well as the extensive occurrence of recombination at all taxonomic levels, from strain to family. The review also presents an overview of the recombination patterns observed in nature that provide some clues regarding the mechanisms involved in the generation and emergence of recombinant genomes. Moreover, the results of experimental evolution studies that support some of the conclusions obtained in descriptive or in silico works are summarized. Finally, the review uses a number of case studies to illustrate those recombination events with evolutionary and pathological implications as well as recombination events in which DNA satellites are involved.

Identification and characterization of a new geminivirus from soybean plants and determination of V2 as a pathogenicity factor and silencing suppressor

BACKGROUND

Soybean is one of the four major crops in China. The occurrence of viruses in soybean causes significant economic losses.

RESULTS

In this study, the soybean leaves from stay-green plants showing crinkle were collected for metatranscriptomic sequencing. A novel geminivirus, tentatively named soybean geminivirus A (SGVA), was identified in soybean stay-green plants. Sequence analysis of the full-length SGVA genome revealed a genome of 2762 nucleotides that contain six open reading frames. Phylogenetic analyses revealed that SGVA was located adjacent to the clade of begomoviruses in both the full genome-based and C1-based phylogenetic tree, while in the CP-based phylogenetic tree, SGVA was located adjacent to the clade of becurtoviruses. SGVA was proposed as a new recombinant geminivirus. Agroinfectious clone of SGVA was constructed. Typical systemic symptoms of curly leaves were observed at 11 dpi in Nicotiana benthamiana plants and severe dwarfism was observed after 3 weeks post inoculation. Expression of the SGVA encoded V2 and C1 proteins through a potato virus X (PVX) vector caused severe symptoms in N. benthamiana. The V2 protein inhibited local RNA silencing in co-infiltration assays in GFP transgenic 16C N. benthamiana plants. Further study revealed mild symptoms in N. benthamiana plants inoculated with SGVA-ZZ _V2-STOP and SGVA-ZZ _V2-3738AA mutants. Both the relative viral DNA and CP protein accumulation levels significantly decreased when compared with SGVA-inoculated plants.

CONCLUSIONS

This work identified a new geminivirus in soybean stay-green plants and determined V2 as a pathogenicity factor and silencing suppressor.

African Basil (Ocimum gratissimum) Is a Reservoir of Divergent Begomoviruses in Uganda

Begomoviruses are plant viruses that cause major losses to many economically important crops. Although they are poorly understood, begomoviruses infecting wild plants may have an important role as reservoirs in the epidemiology of viral diseases. This study reports the discovery and genomic characterization of three novel bipartite begomoviruses from wild and cultivated African basil (Ocimum gratissimum) plants collected in Uganda, East Africa. Based on the symptoms shown by the infected plants, the names proposed for these viruses are Ocimum yellow vein virus (OcYVV), Ocimum mosaic virus (OcMV), and Ocimum golden mosaic virus (OcGMV). Genome and phylogenetic analyses suggest that DNA-A of OcGMV is mostly related to begomoviruses infecting tomato in Africa, whereas those of OcYVV and OcMV are closely related to one another and highly divergent within the Old World begomoviruses. The DNA-A of all characterized begomovirus isolates are of a recombinant nature, revealing the role of recombination in the evolution of these begomoviruses. The viruses characterized here are the first identified in O. gratissimum and the first in Ocimum spp. in the African continent and could have important epidemiological consequences for cultivated basils and other important crops.[Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Analysis of DNAs associated with coconut foliar decay disease implicates a unique single-stranded DNA virus representing a new taxon

The unique ecology, pathology and undefined taxonomy of coconut foliar decay virus (CFDV), found associated with coconut foliar decay disease (CFD) in 1986, prompted analyses of old virus samples by modern methods. Rolling circle amplification and deep sequencing applied to nucleic acid extracts from virion preparations and CFD-affected palms identified twelve distinct circular DNAs, eleven of which had a size of about 1.3 kb and one of 641 nt. Mass spectrometry-based protein identification proved that a 24 kDa protein encoded by two 1.3 kb DNAs is the virus capsid protein with highest sequence similarity to that of grabloviruses (family Geminiviridae), even though CFDV particles are not geminate. The nine other 1.3 kb DNAs represent alphasatellites coding for replication initiator proteins that differ clearly from those encoded by nanovirid DNA-R. The 641 nt DNA-gamma is unique and may encode a movement protein. Three DNAs, alphasatellite CFDAR, capsid protein encoding CFDV DNA-S.1 and DNA-gamma share sequence motifs near their replication origins and were consistently present in all samples analysed. These DNAs appear to be integral components of a possibly tripartite CFDV genome, different from those of any Geminiviridae or Nanoviridae family member, implicating CFDV as representative of a new genus and family.