Under siege: virus control in plant meristems and progeny

Abstract

In the arms race between plants and viruses, two frontiers have been utilized for decades to combat viral infections in agriculture. First, many pathogenic viruses are excluded from plant meristems, which allows the regeneration of virus-free plant material by tissue culture. Second, vertical transmission of viruses to the host progeny is often inefficient, thereby reducing the danger of viral transmission through seeds. Numerous reports point to the existence of tightly linked meristematic and transgenerational antiviral barriers that remain poorly understood. In this review, we summarize the current understanding of the molecular mechanisms that exclude viruses from plant stem cells and progeny. We also discuss the evidence connecting viral invasion of meristematic cells and the ability of plants to recover from acute infections. Research spanning decades and performed on a variety of virus/host combinations has made clear that, beside morphological barriers, RNA interference (RNAi) plays a crucial role in preventing – or allowing – meristem invasion and vertical transmission. How a virus interacts with plant RNAi pathways in the meristem has profound effects on its symptomatology, persistence, replication rates, and, ultimately, entry into the host progeny.

Impacts of RNA Mobility Signals on Virus Induced Somatic and Germline Gene Editing

“…In addition to plant factors, viral factors can also have a role in allowing a virus to access the meristem. For example, viral suppressors of RNA silencing (VSR) are capable of overcoming antiviral barriers in the SAM ( Bradamante et al, 2021 ), and could be adopted from known seed transmissible viruses to existing systems to facilitate germline mutations. In BSMV and TRV, VSRs have been identified.…”

“…In BSMV and TRV, VSRs have been identified. The BSMV γb protein mediates vertical transmission, and the 16K protein from TRV is involved in meristem invasion, ultimately resulting in seed transmissibility ( Bradamante et al, 2021 ). The SAM utilizes several defense mechanisms to preclude viral invasion including the expression of resistance genes, autophagy, and RNA interference ( Bradamante et al, 2021 ).…”

“…The BSMV γb protein mediates vertical transmission, and the 16K protein from TRV is involved in meristem invasion, ultimately resulting in seed transmissibility ( Bradamante et al, 2021 ). The SAM utilizes several defense mechanisms to preclude viral invasion including the expression of resistance genes, autophagy, and RNA interference ( Bradamante et al, 2021 ). Another mechanism that was recently found to permit SAM entry, involved silencing of the WUSCHEL (WUS) transcription factor, which normally protects the SAM from virus infection by inhibiting viral protein synthesis, which results in broad-spectrum protection against viral infection ( Wu et al, 2020 ).…”

Detection and elimination of viruses infecting sweet potatoes in Hungary

“…The symptomless infection, low titre, and tenacity in the cytoplasm of meristematic cells after heat treatment suggest that SPPV is a persistent virus causing latent infection in sweet potato (Bradamante et al, 2021;Kreuze et al, 2020;Roossinck, 2012;Takahashi et al, 2019). The SPPV-sweet potato relationship is possibly symbiotic because the virus is "allowed" to invade seeds and meristematic cells of sweet potato (Kreuze et al, 2020;Roossinck, 2008Roossinck, , 2012Takahashi et al, 2019).…”

Challenges Facing CRISPR/Cas9-Based Genome Editing in Plants

“…TRV is a member of the Tobravirus genus, whose genomes consist of bipartite positive-strand RNAs and can infect over 400 plant species. Its wide range of hosts, together with systemic virus movement to all plant tissues including the germline and meristematic tissue, suggested that TRV might be a useful viral vector for genome engineering ( Bradamante et al, 2021 ). Indeed, the transient expression of the TRV-based vector in jasmine tobacco ( N. alata ) delivered meganuclease to the dihydroflavonol 4-reductase ( DFR ) gene and introduced mutations at the desired target site in reproductive organs such as pollen grains with low frequency ( Honig et al, 2015 ).…”