The genomic sequence and biological properties of Pennisetum mosaic virus, a novel monocot-infecting potyvirus

Complete Genome Characterization and Coat Protein Genealogy of Isolates of Maize dwarf mosaic virus from Johnsongrass and Maize in Oklahoma and Missouri

Maize dwarf mosaic virus (MDMV) significantly affects maize production worldwide, including the United States. This study describes the distribution and biological and molecular characterization of MDMV isolates from Johnsongrass and maize. A total of 262 samples (symptomatic = 214, asymptomatic = 48) were collected in Oklahoma and Missouri during 2016, 2017, and 2019 growing seasons. Based on a dot-immunobinding assay (DIBA), the average incidence of maize dwarf mosaic disease varied from ∼71% (79/111) in 2016, ∼76% (81/106) in 2017, and 62% (28/45) in 2019. Sixty-five DIBA-positive samples for MDMV were further confirmed by RT-PCR, and the complete coat protein (CP) gene was cloned and sequenced. Phylogenetic analysis of 132 isolates (This study = 65; GenBank = 67) revealed two main groups (G1 and G2) of MDMV isolates. All 65 MDMV isolates contained a 39-nucleotide insertion in the N-terminal region of CP genes and clustered in G1 which were different from the isolates in G2, without 39-nucleotide insertion. The first complete genome (9,563 nucleotides) of a MDMV isolate (Bixby1) from Johnsongrass was sequenced, which was distantly related to eight previously reported MDMV isolates from maize. The dN/dS ratio showed mostly purifying selection on each of cistrons except 6K1 being subjected to the diversifying selection. Further analyses revealed three putative recombination events between MDMV-Bixby1 and MDMV isolates from other countries. The successful mechanical and aphid transmission of MDMV-Bixby1 onto maize cultivars was achieved. Altogether, this information showed that Johnsongrass harbors genetically diverse MDMV isolates, which could pose a threat to cultivated crops such as maize and sorghum.

Molecular characterization reveals that squash chlorosis mottling virus and zucchini tigré mosaic virus are the same newly emerging potyvirus

In 2013, we published the first report of a novel potyvirus isolate, which was tentatively named squash chlorosis mottling virus (SqCMV), from an infected squash plant (Cucurbita pepo) collected in the Homestead area of Florida. The purpose of the current work was to further characterize the virus isolate based on molecular properties, and to determine its relationship to other potyviruses. The complete genome sequence of the virus was 10,292 nucleotides (nt), consisting of a 5'-UTR (182 nt), a complete ORF (10,098 nt) encoding a polyprotein of 3,365 amino acids, a motif for the PIPO protein and a 3'-UTR (112 nt), but excluding the poly-(A) tail. Phylogenetic analysis based on the complete genome and amino acid sequences revealed that the virus from Florida clustered with the type isolate of the newly described potyvirus zucchini tigré mosaic virus (ZTMV) sharing 82-90% nucleotide and 83-86% amino acid identities, respectively. Recombination analysis confirmed one major recombination event in the putative P1 coding region of the virus with the putative parental sequences predicted to resemble to ZTMV-Venezuela and France isolates. In addition, genetic diversity analysis indicated that the CP gene was under the highest selection pressure compared to other genes. Together, these results suggest that SqCMV and ZTMV are both representative isolates of the same species, Zucchini tiger mosaic virus. We present the first complete genome sequence of the ZTMV-HFL isolate from the USA.

Complete genomic sequence of common reed chlorotic stripe virus, a novel member of the family Potyviridae

Common reed (Phragmites australis) plants showing chlorotic stripe symptoms on leaves were found in Gansu Province, China. Deep sequencing of small RNAs from symptomatic leaves identified a putative potyvirus, which was named common reed chlorotic stripe virus (CRCSV). The full genome sequence was determined by reverse transcription PCR, rapid amplification of cDNA ends (RACE) PCR, and sequencing. It consists of 9,426 nucleotides, excluding the poly(A) tail, and contains a large open reading frame encoding a polyprotein of 3,014 amino acids. Putative proteolytic cleavage sites were identified. Since CRCSV shared low sequence similarity (35%-37% identity) to any known members of the family Potyviridae and it clustered uniquely in phylogenetic analysis of either the polyprotein or the coat protein, CRCSV is a distinct, previously undescribed member of the family Potyviridae.

Possible involvement of maize Rop1 in the defence responses of plants to viral infection

The expression of host genes can be altered during the process of viral infection. To investigate the viral infection-induced up-regulated gene expression changes of maize at different time intervals post-inoculation with Sugarcane mosaic virus (SCMV), a suppression subtractive hybridization cDNA library was constructed. A total of 454 cDNA clones were identified to be viral infection-induced up-regulated genes. The influence of Rop1 on the infection of maize by SCMV was investigated. The results showed that transient silencing of the ZmRop1 gene through virus-induced gene silencing enhanced the accumulation and systemic infection of SCMV and another potyvirus (Pennisetum mosaic virus) in maize plants, whereas transient over-expression of ZmRop1 in maize protoplasts reduced SCMV accumulation. Furthermore, it was demonstrated that the heterologous expression of ZmRop1 impaired Potato virus X infection in Nicotiana benthamiana plants. These data suggest that ZmRop1 may play a role in plant defence responses to viral infection.