Isolation of a novel SUMO protein from tomato that suppresses EIX-induced cell death

Challenging tomato or tobacco varieties with ethylene-inducing xylanase (EI X) from the fungus Trichoderma viride causes rapid induction of plant defen ce responses leading to programmed cell death. Using the yeast two-hybrid s ystem, we isolated a novel protein, tomato small ubiquitin-related modifier protein (T-SUMO), which specifically interacts with EIX. T-SUMO, a cytopla smic protein, is a member of the ubiquitin-like protein family. It shows ho mology to human protein sentrin/SUMO1, which suppresses tumour necrosis fac tor-induced cell death. Transgenic plants that express T-SUMO in the sense orientation suppress EIX induction of ethylene biosynthesis and cell death, while in the antisense orientation they enhance EIX-induced ethylene biosy nthesis. These results indicate that T-SUMO is involved in mediating the si gnal generated by EIX that leads to induction of plant defence responses.