Distribution and Location of BEVs in Different Genotypes of Bananas Reveal the Coevolution of BSVs and Bananas.

Members of the family Caulimoviridae contain abundant endogenous pararetroviral sequences (EPRVs) integrated into the host genome. Banana streak virus (BSV), a member of the genus Badnavirus in this family, has two distinct badnaviral integrated sequences, endogenous BSV (eBSV) and banana endogenous badnavirus sequences (BEVs). BEVs are distributed widely across the genomes of different genotypes of bananas. To clarify the distribution and location of BEVs in different genotypes of bananas and their coevolutionary relationship with bananas and BSVs, BEVs and BSVs were identified in 102 collected banana samples, and a total of 327 BEVs were obtained and categorized into 26 BEVs species with different detection rates. However, the majority of BEVs were found in Clade II, and a few were clustered in Clade I. Additionally, BEVs and BSVs shared five common conserved motifs. However, BEVs had two unique amino acids, methionine and lysine, which differed from BSVs. BEVs were distributed unequally on most of chromosomes and formed hotspots. Interestingly, a colinear relationship of BEVs was found between AA and BB, as well as AA and SS genotypes of bananas. Notably, the chromosome integration time of different BEVs varied. Based on our findings, we propose that the coevolution of bananas and BSVs is driven by BSV Driving Force (BDF), a complex interaction between BSVs, eBSVs, and BEVs. This study provides the first clarification of the relationship between BEVs and the coevolution of BSVs and bananas in China.

Genetic diversity of banana bunchy top virus isolates from China.

Banana bunchy top virus (BBTV) (the genus Babuvirus, the family Nanoviridae) is a single-stranded circular DNA virus with a genome composed of six components designated as DNA-R, -U3, -S, -M, -C, and -N. This study analyzed the nucleotide identities of the DNA-R of 23 isolates from banana-producing provinces of China, including Guangdong, Hainan, Guangxi, and Yunnan. Results showed that the nucleotide identity of DNA-R was 72.3-100%. Phylogenetic analysis indicated that these BBTV isolates were clustered in different subgroups within the Asian group (AG). Sequence analysis of the five other components (DNA -U3, -S, -M, -C, and -N) of the five isolates from China confirmed the results established for DNA-R of these BBTV isolates. This study suggested that the variation of DNA-R from Chinese BBTV isolates was considerably higher than the variation of other AG isolates, but their genetic diversity was low.

Development of SYBR Green I Based Real-Time RT-PCR Assay for Specific Detection of Watermelon silver mottle Virus.

BACKGROUND: Watermelon silver mottle virus (WSMoV), which belongs to the genus Tospovirus, causes significant loss in Cucurbitaceae plants. OBJECTIVES: Development of a highly sensitive and reliable detection method for WSMoV. MATERIALS AND METHODS: Recombinant plasmids for targeting the sequence of nucleocapsid protein gene of WSMoV were constructed. SYBR Green I real-time PCR was established and evaluated with standard recombinant plasmids and 27 watermelon samples showing WSMoV infection symptoms. RESULTS: The recombinant plasmid was used as template for SYBR Green I real-time PCR to generate standard and melting curves. Melting curve analysis indicated no primer-dimers and non-specific products in the assay. No cross-reaction was observed with Capsicum chlorosis virus (genus Tospovirus) and Cucumber mosaic virus (genus Cucumovirus). Repeatability tests indicated that inter-assay variability of the Ct values was 1.6%. CONCLUSIONS: A highly sensitive, reliable and rapid detection method of SYBR Green I real-time PCR for timely detection of WSMoV plants and vector thrips was established, which will facilitate disease forecast and control.

Complete genome sequence of a Watermelon silver mottle virus isolate from China.

The complete genome of a Watermelon silver mottle virus (WSMoV) (genus Tospovirus, family Bunyaviridae) isolate (WSMoV-GZ) from Guangdong province, China was sequenced. The genomes of WSMoV-GZ contained 3,603, 4,909, and 8,914 nt of small (S), medium (M), and large (L) RNA segments, respectively, and had a genomic organization characteristic of members of the genus Tospovirus. The amino acid sequence of the nucleocapsid (N) protein, S RNA-encoded nonstructural (NSs) protein, M RNA-encoded nonstructural (NSm) protein, Gn/Gc glycoprotein precursor, and RNA-dependent RNA polymerase (RdRp) protein showed 94.3-97.5 % identity with those of other WSMoV isolates. Phylogenetic analysis showed that the N protein of WSMoV-GZ was clustered together with those of the WSMoV isolates. The full sequence of WSMoV-GZ provides a reference genome for comparison with other tospoviruses.