Functional characterization of Mi, a root-knot nematode resistance gene from tomato (Lycopersicon esculentum L.)

Root-knot nematodes (Meloidogyne spp.) cause major economic damage to numerous crop species around the world. Plant resistance is the most important attribute that is able to suppress invasion by the root-knot nematodes. In the present study,, a candidate root-knot nematode resistance gene (M) was isolated from the resistant tomato (Lycopersicon esculentum, L.) line RN-1. Expression profiling analysis revealed that this gene was expressed specifically in the roots, stems, and leaves, but not in the flowers or fruits. To verify the real function of this candidate gene, both sense and inteference RNA (RNAi) vectors were constructed. We obtained 31 transgenic plants with between one and seven copies of T-DNA inserts of sense Mi from two nematode-susceptible tomato cultivars as assayed by polymerase chain reaction (PCR) and Southern blotting analysis. Reverse transcription-PCR analysis revealed that expression levels of the Mi gene varied in different transgenic plants. Nematode assays showed that the resistance to root-knot nematodes was significantly improved in some transgenic lines compared with untransformed susceptible controls and that the resistance was heritable in selfed progeny. Loss of function via RNAi further confirmed the role of the Mi gene and the original resistant lines became susceptible to root-knot nematodes.