Molecular cloning and characterisation of a venom allergen AG5-like cDNA from Meloidogyne incognita.

RNA fingerprinting was used to identify RNAs that were expressed in parasitic second-stage juveniles of Meloidogyne incognita, but absent from or reduced in preparasitic second-stage juveniles. A cDNA encoding a putative secretory protein was cloned from a M. incognita second-stage juvenile cDNA library by probing with a 0.5kb fragment derived from fingerprinting that was more strongly expressed in parasitic second-stage juveniles. The cDNA, named Mi-msp-1, contained an open reading frame encoding 231 amino acids, with the first 21 amino acids being a putative secretory signal. In Southern blot analysis the Mi-msp-1 hybridised with genomic DNA from M. incognita, Meloidogyne arenaria, Meloidogyne javanica, but not Meloidogyne hapla, Heterodera glycines or Caenorhabditis elegans. In Northern blot analysis a 1kb transcript was detected in both preparasitic and parasitic second-stage juveniles, but not in adult females of M. incognita. Comparing the predicted amino acid sequence with protein databases revealed significant similarity to the venom allergen antigen 5 family of proteins in hymenoptera insects and homologues found in several other nematode species.