Understanding tobamovirus-plant interactions: implications for breeding resistance to tomato brown rugose fruit virus

Abstract

The genus Tobamovirus comprises a group of single-stranded RNA viruses that affect a wide variety of vegetables of economic importance. Tobamoviruses express a series of proteins that interact with the plant’s cellular machinery, allowing viral infection; during incompatible interactions, active defense is mediated by host proteins encoded by resistance genes. The genes conferring viral resistance and tolerance in non-susceptible hosts have been studied for their ability to transfer desired resistance traits to different crops. The N gene from Nicotiana spp., the repertoire of Tm genes in Solanum spp., the L locus from Capsicum spp., and TOM genes are the most studied genetic sequences for understanding resistance to tobamoviruses. Through classical plant breeding and genetic engineering techniques, it has been possible to introgress these resistance genes (R) into new species. However, new reports highlight the ability of tobamoviruses to overcome R-mediated defense. One of the most notorious recent cases is the tomato brown rugose fruit virus (ToBRFV). The main characteristic of ToBRFV is its capacity to overcome the resistance mediated by the Tm-22 gene, resulting in a limited repertoire of options to combat the virus. To defeat emerging viruses, it is necessary to apply the knowledge from other tobamoviruses-host relationships and use new technologies such as genome-wide association studies (GWAS) to understand and associate the architecture of resistance genes present in the Solanaceae family for the benefit of plant breeding. Although new genomic tools such as CRISPR systems open the possibility of coping with viral diseases, there are no commercial ToBRFV-resistant tomato varieties. Hence, the world’s leading seed suppliers compete to develop and bring these varieties to market.