Synergy between an emerging monopartite begomovirus and a DNA-B component

In recent decades, a legion of monopartite begomoviruses transmitted by the whitefly Bemisia tabaci has emerged as serious threats to vegetable crops in Africa. Recent studies in Burkina Faso (West Africa) reported the predominance of pepper yellow vein Mali virus (PepYVMLV) and its frequent association with a previously unknown DNA-B component. To understand the role of this DNA-B component in the emergence of PepYVMLV, we assessed biological traits related to virulence, virus accumulation, location in the tissue and transmission. We demonstrate that the DNA-B component is not required for systemic movement and symptom development of PepYVMLV (non-strict association), but that its association produces more severe symptoms including growth arrest and plant death. The increased virulence is associated with a higher viral DNA accumulation in plant tissues, an increase in the number of contaminated nuclei of the phloem parenchyma and in the transmission rate by B. tabaci. Our results suggest that the association of a DNA-B component with the otherwise monopartite PepYVMLV is a key factor of its emergence.

Identification and Functional Analysis of Four RNA Silencing Suppressors in Begomovirus Croton Yellow Vein Mosaic Virus

Croton yellow vein mosaic virus (CYVMV), a species in the genus Begomovirus, is a prolific monopartite begomovirus in the Indian sub-continent. CYVMV infects multiple crop plants to cause leaf curl disease. Plants have developed host RNA silencing mechanisms to defend the threat of viruses, including CYVMV. We characterized four RNA silencing suppressors, namely, V2, C2, and C4 encoded by CYVMV and betasatellite-encoded C1 protein (βC1) encoded by the cognate betasatellite, croton yellow vein betasatellite (CroYVMB). Their silencing suppressor functions were verified by the ability of restoring the β-glucuronidase (GUS) activity suppressed by RNA silencing. We showed here for the first time that V2 was capable of self-interacting, as well as interacting with the V1 protein, and could be translocalized to the plasmodesmata in the presence of CYVMV. The knockout of either V2 or V1 impaired the intercellular mobility of CYVMV, indicating their novel coordinated roles in the cell-to-cell movement of the virus. As pathogenicity determinants, each of V2, C2, and C4 could induce typical leaf curl symptoms in Nicotiana benthamiana plants even under transient expression. Interestingly, the transcripts and proteins of all four suppressors could be detected in the systemically infected leaves with no correlation to symptom induction. Overall, our work identifies four silencing suppressors encoded by CYVMV and its cognate betasatellite and reveals their subcellular localizations, interaction behavior, and roles in symptom induction and intercellular virus movement.

Tobacco Leaf Curl Puer Virus: a Novel Monopartite Begomovirus Infecting Nicotiana Tabacum in China

Begomoviruses (family Geminiviridae) cause serious diseases in many economic crops and weeds globally. This study characterized a begomovirus isolated from a tobacco plant with leaf curl in Puer, Yunnan Province, China. Analysis of the viral genome obtained from a diseased Nicotiana tabacum plant showed a novel monopartite begomovirus. The DNA-A-like sequence (2741 nt) has the typical Old World monopartite begomovirus genome organization, sharing the highest nucleotide sequence identity (81.2%) with that of Tomato yellow leaf curl Vietnam virus (TYLCVV). According to the current International Committee on Taxonomy of Viruses (ICTV )taxonomic criteria, this is a new species of begomovirus for which the name “Tobacco leaf curl Puer virus” is proposed.

In Planta Interaction and Transreplication of Distinct Begomoviruses and their Associated Components

The studies described here were intended to examine the transreplication and interactions abilities of a widespread ToLCNDV, and an emerging begomovirus PeLCV associated with its cognate betasatellite TbLCuB. PeLCV, a monopartite begomovirus, has been characterized from many important crops, vegetables and weeds along with its associated TbLCuB. The DNA-B of bipartite ToLCNDV genome has been successfully transreplicated by the DNA-A of different bipartite begomoviruses, albeit with low frequency. Whether PeLCV can transreplicate DNA-B of ToLCNDV is unknown. To unravel this notion, both these viruses were inoculated to the model Nicotiana benthamiana plants in all possible combinations and the in planta existence of viral components were verified by PCR and Southern blot hybridization. The results demonstrated that PeLCV transreplicated and maintained ToLCNDV DNA-B. Whereas, ToLCNDV DNA-A could not transreplicate TbLCuB. Analyses of Rep proteins structure of ToLCNDV and PeLCV revealed a structural resemblance, whereas putative iteron-binding sequences of PeLCV were compatible with the Rep-binding iterons of ToLCNDV-B. The results suggested that PeLCV and ToLCNDV DNA-B can interact synergistically and can be disastrous under field conditions. © 2021 Friends Science Publishers