Enhanced resistance to potato virus Y (PVY) and resistance-breaking PVY in tobacco eIF4E-S and eIF(iso)4E-T double mutant
Eukaryotic translation-initiation factors in plants, eIF4E and eIF(iso)4E, play key roles in infection by potyviruses and other plant RNA viruses. Mutations in the genes encoding these factors might reduce susceptibility to viruses. They are the basis of several recessive virus-resistance genes that are used widely in plant breeding. In tobacco (Nicotiana tabacum L.), deletion mutants of eIF4E-S have been used as sources of resistance to Potato virus Y (PVY; the type member of the genus Potyvirus). However, emergence of resistance-breaking strains of PVY (RB-PVY) has been reported worldwide. In an earlier study, we demonstrated that loss-of-function of a tobacco eIF(iso)4E-T gene reduces susceptibility to a RB-PVY. Here, we demonstrated that knock out of both eIF4E-S and eIF(iso)4E-T confer enhanced resistance to both PVY and RB-PVY. By crossing an eIF(iso)4E mutant with a variety TN90, which lost eIF4E-S, plants without functional eIF4E-S and eIF(iso)4E-T were obtained. When PVY and RB-PVY were inoculated, TN90 and eIF(iso)4E-T mutant respectively showed resistance to PVY and RB-PVY. They showed no necrotic symptoms seven days after the inoculation (DAI), but showed symptoms 14 DAI. However, the eIF4E-S and eIF(iso)4E-T double mutant showed enhanced resistance to both viruses: necrotic symptoms were not observed, even at 28 DAI. Consequently, the effect of simultaneous lack of functional eIF4E-S and eIF(iso)4E-T genes on virus resistance was synergistic. The eIF4E-S and eIF(iso)4E-T double mutant is expected to be useful for breeding of PVY-resistant and RB-PVY-resistant tobacco.