Occurrence and Genetic Diversity of Grapevine berry inner necrosis virus from Grapevines in China

Identification of Vitis vinifera MYB transcription factors and their response against grapevine berry inner necrosis virus

BACKGROUND

The myeloblastosis (MYB) superfamily is the largest transcription factor family in plants that play diverse roles during stress responses. However, the biotic stress-responsive MYB transcription factors of the grapevine have not been systematically studied. In China, grapevine berries are often infected with the grapevine berry inner necrosis virus (GINV), which eventually reduces the nutritional quality and commodity value.

RESULTS

The present study identified and characterized 265 VvMYB or VvMYB-related genes of the "Crimson seedless" grapevine. Based on DNA-binding domain analysis, these VvMYB proteins were classified into four subfamilies, including MYB-related, 2R-MYB, 3R-MYB, and 4R-MYB. Phylogenetic analysis divided the MYB transcription factors into 26 subgroups. Overexpression of VvMYB58 suppressed GINV abundance in the grapevine. Further qPCR indicated that among 41 randomly selected VvMYB genes, 12 were induced during GINV infection, while 28 were downregulated. These findings suggest that VvMYB genes actively regulate defense response in the grapevine.

CONCLUSION

A deeper understanding of the MYB TFs engaged in GINV defense response will help devise better management strategies. The present study also provides a foundation for further research on the functions of the MYB transcription factors.

Phylogenetic and Evolutionary Studies of Grapevine Pinot Gris Virus Isolates from Canada

This study investigated the phylogenetic relationship of grapevine Pinot gris virus (GPGV) isolates from Canada with GPGV isolates reported worldwide. Full-length genomes of 25 GPGV isolates representing the main four grape-growing regions in Canada (British Columbia, Ontario, Nova Scotia and Quebec) were sequenced and compared to genomes of 43 GPGV isolates representing eight countries and three continents. Phylogenetic analysis based on full genome sequences revealed an unambiguous separation of North American GPGV isolates with isolates from Europe and Asia. Within the North American clade, GPGV isolates from the USA segregated into a distinct subclade, whereas the relationships amongst GPGV isolates from different regions of Canada were not clearly defined. The phylogenetic analysis of the overlapping regions of MP and CP genes involving 169 isolates from 14 countries resulted in two distinctive clades, which were seemingly independent of their country of origin. Clade 1 included the majority of asymptomatic isolates (81% asymptomatic), whereas clade 2 was predominantly formed of symptomatic isolates (78% symptomatic). This research is the first study focused on the genetic variability and origin of GPGV in Canada.

Emerging and population analysis of Grapevine Pinot gris virus isolates from Iran

Grapevine Pinot gris virus (GPGV) is a novel member of Trichovirus genus in Betaflexiviridae family. During 2018-2019, 114 leaf and green shoot samples were collected from the main vineyards in Iran Zanjan, Hamedan and East Azerbaijan provinces. After total RNA extraction and cDNA synthesis, the samples were tested by PCR assay using two pairs of specific primers corresponding to the coat protein (CP) and movement protein (MP) regions of GPGV, in which 6 out of 114 samples were found to be infected by GPGV. Population genetics analysis and molecular evolution of GPGV were done based on the CP and MP gene sequences of six new Iranian isolates and 53 additional isolates from several different countries in three continents: Asia, Europe, and America. The phylogenetic tree of GPGV isolates was clustered into two independent clades with significant F _ST values (> 0.44). The ω values were calculated < 1 for the GPGV isolates for both genes. These findings demonstrated that the GPGV evolutionary selection pressure is under negative selection. To our knowledge, this is the first detailed study on the molecular characterization, phylogenetic analysis, and provide a better understanding of the population evolution of GPGV isolates from vineyards in Iran. The new Iranian isolates were lied in a new cluster near to European isolates.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02914-5.

Identification and Characterization of a Novel Emaravirus From Grapevine Showing Chlorotic Mottling Symptoms

A novel negative-sense, single-stranded (ss) RNA virus was identified in a “Shennong Jinhuanghou” (SJ) grapevine showing severe chlorotic mottling symptoms by integrating high-throughput sequencing (HTS) and conventional Sanger sequencing of reverse transcription polymerase chain reaction (RT-PCR) products. The virus was provisionally named as “grapevine emaravirus A” (GEVA). GEVA had a genome comprising five genomic RNA segments, each containing a single open reading frame on the viral complementary strand and two untranslated regions with complementary 13- nt stretches at the 5′ and 3′ terminal ends. RNA1 (7,090 nt), RNA2 (2,097 nt), RNA3 (1,615 nt), and RNA4 (1,640 nt) encoded putative proteins P1–P4 that, based on their conserved motifs, were identified as the RNA-dependent RNA polymerase, glycoprotein, nucleocapsid protein, and movement protein, respectively. However, the functional role of protein P5 encoded by RNA5 (1,308 nt) could not be determined. Phylogenetic trees constructed based on amino acids of P1 to P4, allocated GEVA in clade I, together with other species-related emaraviruses. These data support the proposal that GEVA is a representative member of a novel species in the genus Emaravirus of the family Fimoviridae. Moreover, when GEVA was graft-transmitted to SJ and “Beta” grapevines, all grafted plants showed the same symptoms, similar to those observed in the source of the inoculum. This is the first report to our knowledge of an emaravirus infecting grapevine and its possible association with chlorotic mottling symptoms.

Development of a Full-Length Infectious cDNA Clone of the Grapevine Berry Inner Necrosis Virus

Grapevine berry inner necrosis virus (GINV) belongs to the genus Trichovirus in the family Betaflexiviridae. The GINV isolate LN_BETA_RS was obtained from a “Beta” grapevine (Vitis riparia × Vitis labrusca) exhibiting chlorotic mottling and ring spot in Xingcheng, Liaoning Province, China. To verify the correlation between GINV and grapevine chlorotic mottling and ring spot disease, we constructed an infectious cDNA clone of GINV isolate LN_BETA_RS using the seamless assembly approach. Applied treatments of agroinfiltration infectious cDNA confirmed systemic GINV infection of the Nicotianaoccidentalis 37B by reverse transcription polymerase chain reaction (RT-PCR) and transmission electron microscopy, exhibiting chlorotic mottling symptoms on leaves. Infectious cDNA was also transmitted to new healthy N. occidentalis plants through rub-inoculation. Moreover, the cDNA clone was agroinfiltrated into “Beta” and “Thompson Seedless” grapevine plantlets, and the inoculated grapevines exhibited leaf chlorotic mottling and ringspot during the two years of observation. GINV-inoculated “Beta” grapevines had serious leaf chlorotic mottling and ringspot symptoms on the whole plant, while relatively few symptoms were observed on the leaves of agroinoculated “Thompson Seedless” grapevines in early spring and only weak ring spot gradually appeared later in the top young leaves. Our experiments fulfilled Koch’s postulates and revealed the causative role of GINV in grapevine chlorotic mottling and ring spot disease.

Pest categorisation of non-EU viruses and viroids of Vitis L

Following a request from the EU Commission, the Panel on Plant Health addressed the pest categorisation of the viruses and viroids of Vitis L. determined as being either non-EU or of undetermined standing in a previous EFSA opinion. These infectious agents belong to different genera and are heterogeneous in their biology. With the exclusion of grapevine virus 101-14.N.23.9.1/South Africa/2009 for which very limited information exists, the pest categorisation was completed for 30 viruses or viroids having acknowledged identities and available detection methods. All these viruses are efficiently transmitted by vegetative propagation techniques, with plants for planting representing the major pathway for long-distance dispersal and thus considered as the major pathway for potential entry. Depending on the virus, additional pathway(s) can also be seeds, pollen and/or vector(s). Most of the viruses categorised here are known to infect only one or few plant genera, but some of them have a wide host range, thus extending the possible entry pathways. Grapevine yellow speckle viroid 2, blueberry leaf mottle virus, grapevine Ajinashika virus, grapevine Anatolian ringspot virus, grapevine berry inner necrosis virus, grapevine deformation virus, grapevine fabavirus, grapevine red blotch virus, grapevine stunt virus, grapevine Tunisian ringspot virus, grapevine vein-clearing virus, temperate fruit decay-associated virus, peach rosette mosaic virus, tobacco ringspot virus, tomato ringspot virus meet all the criteria evaluated by EFSA to qualify as potential Union quarantine pests (QPs). With the exception of impact for the EU territory, on which the Panel was unable to conclude, blackberry virus S, grapevine geminivirus A, grapevine leafroll-associated virus 7, grapevine leafroll-associated virus 13, grapevine satellite virus, grapevine virus E, grapevine virus I, grapevine virus J, grapevine virus S, summer grape enamovirus, summer grape latent virus satisfy all the other criteria to be considered as potential Union QPs. Australian grapevine viroid, grapevine cryptic virus 1, grapevine endophyte endornavirus and wild vitis virus 1 do not meet all the criteria evaluated by EFSA to be regarded as potential Union QPs because they are not known to cause an impact on Vitis. For several viruses, especially those recently discovered, the categorisation is associated with high uncertainties mainly because of the absence of data on their biology, distribution and impact. Since this opinion addresses specifically non-EU viruses, in general these viruses do not meet the criteria assessed by EFSA to qualify as a potential Union regulated non-quarantine pests.