Isolation and characterization of a cDNA encoding a serine proteinase from the root-knot nematode Meloidogyne incognita

This report describes the first serine proteinase gene isolated from the sedentary nematode Meloidogyne incognita. Using degenerate primers, a 1372 bp cDNA encoding a chymotrypsin-like serine proteinase (Mi-ser1) was amplified from total RNA of adult females by RT-PCR and 5′ and 3′ rapid amplification of cDNA ends. The deduced amino acid sequence of Mi-ser1 encoded a putative signal peptide and a prodomain of 22 and 33 amino acids, respectively, and a mature proteinase of 341 amino acids with a predicted molecular mass of 37,680 Da. Sequence identity with the top serine proteinases matches from the databases ranged from 23 to 27%, including sequences from insects, mammals, and other nematodes. Southern blot analysis suggested that Mi-ser1 is encoded by a single or few gene copies. The pattern of developmental expression analyzed by Northern blot and RT-PCR indicated that Mi-ser1 was transcribed mainly in females. The domain architecture composed of a single chymotrypsin-like catalytic domain and the detection of a putative signal peptide suggested a digestive role for Mi-ser1.