Development of an attenuated potato virus Y mutant carrying multiple mutations in helper-component protease for cross-protection.

• A non-aphid-transmissible attenuated PVY triple-mutant PVY-HC ELR was developed. • PVY-HC ELR mutant was stable in tobacco plants. • PVY-HC ELR mutant protected tobacco plants from the severe PVY infection. • Provided the material basis for the management of PVY through cross-protection. Tobacco (Nicotiana tabacum) is one of the major cash crops in China. Potato virus Y (PVY), a representative member of the genus Potyvirus , greatly reduces the quality and yield of tobacco leaves by inducing veinal necrosis. Mild strain-mediated cross-protection is an attractive method of controlling diseases caused by PVY. Currently, there is a lack of effective and stable attenuated PVY mutants. Potyviral helper component-protease (HC-Pro) is a likely target for the development of mild strains. Our previous studies showed that the residues lysine at positions 124 and 182 (K124 and K182) in HC-Pro were involved in PVY virulence, and the conserved KITC motif in HC-Pro was involved in aphid transmission. In this study, to improve the stability of PVY mild strains, K at position 50 (K50) in KITC motif, K124, and K182 were separately substituted with glutamic acid (E), leucine (L), and arginine (R), resulting in a triple-mutant PVY-HC ELR. The mutant PVY-HC ELR had attenuated virulence and did not induce leaf veinal necrosis symptoms in tobacco plants and could not be transmitted by Myzus persicae. Furthermore, PVY-HC ELR mutant was genetically stable after six serial passages, and only caused mild mosaic symptoms in tobacco plants even at 90 days post inoculation. The tobacco plants cross-protected by PVY-HC ELR mutant showed high resistance to the wild-type PVY. This study showed that PVY-HC ELR mutant was a promising mild mutant for cross-protection to control PVY. [ABSTRACT FROM AUTHOR]