Molecular and genetic determinants of plant tolerance to viruses

Viral diseases cause severe damage to cultivated plants, resulting in global crop losses. In the wild, however, plants are typically free of viral disease symptoms despite recurrent infection.

Naturally tolerant plants have a significant viral load, but their growth, development and reproduction are only minimally affected.

The aim of the TolGreen project is to identify viral and host determinants of tolerance by using Arabidopsis-infecting RNA viruses such as Tobacco mosaic virus (TMV) and the related Oilseed rape mosaic virus (ORMV) as models. Certain natural accessions of A. thaliana (Col-0) are tolerant to TMV whereas other ecotypes (Sha) show disease.

By contrast, Col-0 plants infected with ORMV are initially symptomatic but develop tolerance in the new leaves.

The host laboratory demonstrated that this latter tolerance phenotype depends on genes required for the production of primary and secondary siRNAs and also correlates with the loss of the activity of the viral RNA silencing suppressor (VSR).

The tobamoviral VSR proteins inhibit antiviral RNA silencing by sequestration of small interfering RNAs (siRNAs), which inhibits the assembly of the antiviral RNA-induced silencing complex (RISC). Therefore, tolerance may occur when the VSR siRNA binding activity is saturated by host- or virus-derived siRNAs.

Using the latest tools of molecular genetics and proteomics, TolGreen will determine Arabidopsis genes, viral and host-derived siRNAs as well as VSR-interacting proteins that control VSR activity and are involved in tolerance.

Understanding the molecular mechanism of tolerance will provide important tools for the breeding of resilient, virus-tolerant crops for a more sustainable agriculture.