RNA silencing machinery contributes to inability of BSBV to establish infection in Nicotiana benthamiana: evidence from characterization of agroinfectious clones of Beet soil-borne virus

Abstract

Beet soil-borne virus (BSBV) is a sugar beet pomovirus frequently associated with Beet necrotic yellow veins virus, the causal agent of the rhizomania disease. BSBV has been detected in most of the major beet-growing regions worldwide, yet its impact on this crop remains unclear. With the aim to understand the life cycle of this virus and clarify its putative pathogenicity, agroinfectious clones have been engineered for each segment of its tripartite genome. The biological properties of these clones were then studied on different plant species. Local infection was obtained on agroinfiltrated leaves of Beta macrocarpa. On leaves of Nicotiana benthamiana, similar results were obtained, but only when heterologous viral suppressors of RNA silencing were co-expressed or in a transgenic line down regulated for both dicer-like protein 2 and 4. On sugar beet, local infection following agroinoculation was obtained on cotyledons, but not on other tested plant parts. Nevertheless, leaf symptoms were observed on this host via sap inoculation. Likewise, roots were efficiently mechanically infected, highlighting low frequency of root necrosis and constriction, and enabling the demonstration of transmission by the vector Polymyxa betae. Altogether, the entire viral cycle was reproduced, validating the constructed agroclones as efficient inoculation tools, paving the way for further studies on BSBV and its related pathosystem.

The Beta vulgaris‐derived resistance gene Rz2 confers broad‐spectrum resistance against soilborne sugar beet‐infecting viruses from different families by recognizing triple gene block protein 1

“…BSBV is transmitted by the same vector and occurs in mixed infections with BNYVV (Meunier et al, 2003). Foliar symptoms on leaf tissue but no symptom development on root tissue after BSBV infection on sugar beet plants were recently reported by Mahillon et al (2021). Whether BSBV interferes with symptom expression in mixed infection with BNYVV is unknown (Biancardi & Tamada, 2016).…”

First report of Tomato brown rugose fruit virus in tomato in Switzerland

“…Total dsRNA was extracted from infected plant material according to Mahillon et al. (2021) and was subsequently sent for high throughput sequencing on a NovaSeq 6000 platform. A complete ToBRFV genome (6386 nt; OM305070) was assembled from the obtained reads and shared 99.8% nt identity with ToBRFV‐IL (KX619418.1).…”

The sugar beet multi-talented resistance protein Rz2

“…In addition to BNYVV and BSBMV, P. betae also transmits two viruses from the genus Pomovirus, Beet soil-borne virus (BSBV) and Beet virus Q (BVQ). Both viruses are present in mixed infection with BNYVV and at least BSBV is distributed in sugar beet fields throughout the world (Mahillon et al 2021). Members of the genus Pomovirus have a tripartite RNA genome of about 6 kbp, 3-3.5 kbp and 2-2.5 kbp in size and are organized in rod-shaped segments (Barbarossa et al 1992).…”

“…Although BSBV most often occurs in mixed infection with BNYVV, the impact of BSBV infection alone was studied only a few times (McGrann et al 2009). These studies reported about leaf and root symptoms after artificial infection, but the assumption that BSBV is a mild pathogen needs to be further addressed (Kaufmann et al 1993;Mahillon et al 2021;McGrann et al 2009). The second virus belonging to the genus Pomovirus, BVQ, was considered to be a BSBV strain due to a similar host range, transmission and genome organization but was finally assigned as an independent virus species (Koenig et al 1998).…”

“…BSBV is transmitted by the same vector and occurs in mixed infections with BNYVV (Meunier et al, 2003). Foliar symptoms on leaf tissue but no symptom development on root tissue after BSBV infection on sugar beet plants were recently reported by Mahillon et al 2021. Whether BSBV interferes with symptom expression in mixed infection with BNYVV is unknown (Biancardi and Tamada, 2016).…”