Abstract
Tomato brown rugose fruit virus (ToBRFV) overcomes Tm-2(2)-mediated resistance, posing a serious threat to global tomato production. We previously identified that key residues in the movement protein (MP)-H67, N125, K129, A134, I147 and I168 are essential for ToBRFV evasion of Tm-2(2) resistance. However, the underlying mechanisms remain unclear. In Tm-2(2)-transgenic Nicotiana benthamiana plants at later infection stages, MP mutations H67C, N125A, K129Q and A134N abolished ToBRFV-GFP cell-to-cell and systemic movement, whereas I168N abolished ToBRFV-GFP systemic but not cell-to-cell movement, and I147M partially impaired both. Correspondingly, the MP(H67C), MP(N125A), MP(K129Q) and MP(A134N) mutants elicited strong Tm-2(2)-mediated hypersensitive response (HR), MP(I168N) elicited mild HR and MP(I147M) elicited none. Confocal microscopy revealed I147M reduced MP localisation at plasmodesmata in Tm-2(2)-transgenic N. benthamiana leaves. The interaction with Tm-2(2) was weak for wild-type MP and I147M (slightly enhanced), but moderately or strongly enhanced for I168N and the other four mutants. Wild-type MP and MP(I147M) failed to induce Tm-2(2) self-association, MP(I168N) only weakly induced it, whereas the other four markedly induced it. Collectively, these findings demonstrate that ToBRFV evades Tm-2(2)-mediated resistance by attenuating MP-Tm-2(2) interaction strength, thereby avoiding Tm-2(2) self-association and downstream immune activation.