Identification of genes whose transcripts accumulate rapidly in tomato after root-knot nematode infection

Root-knot nematodes (Meloidogyne spp.) penetrate tomato (Lycopersicon esculentum) and other hosts near root tips and migrate intercellularly to the developing vascular tissue where they induce formation of feeding cells or, in the case of resistant tomato, trigger a localized necrosis. To investigate early events in the host response to nematode infection, a seedling inoculation procedure was designed that produced hundreds of root tips synchronously infected with Meloidogyne javanica. RNA extracted from these tips was used to produce a cDNA library. Differential screening of a subset of this cDNA library identified eight cDNA clones representing genes that are reproducibly increased in level after nematode infection. Sequence analysis revealed that two clones correspond to previously isolated genes encoding ascorbate free radical reductase and an extensin. A third appears to encode a peroxidase. A fourth encodes a product similar to a tumor-induced tobacco gene and belongs to the Kunitz trypsin inhibitor family of proteins. Another encodes a protein highly similar to a tobacco LEA5-like protein. Transcripts of all eight genes are present at higher levels after nematode infection in both susceptible and resistant tomato cultivars.