Two chorismate mutase genes from the root-knot nematode Meloidogyne incognita

Parasitism genes encoding secretory proteins expressed in the oesophageal glands of phytoparasitic nematodes play critical roles in nematode invasion of host plants, establishment of feeding sites and suppression of host defences. Two chorismate mutase (CM) genes potentially having a role in one or more of these processes were identified from a Meloidogyne incognita oesophageal gland-cell subtractive cDNA library. These M. incognita enzymes (designated as MI-CM-1 and MI-CM-2) with amino-terminal signal peptides, were significantly similar to chorismate mutases in M.javanica and bacteria. The complementation of an Escherichia coli CM-deficient mutant by the expression of Mi-cm-1 or Mi-cm-2 confirmed their CM activity. In-situ mRNA hybridization showed that the transcripts of Mi-cm-1 and Mi-cm-2 accumulated specifically in the two subventral oesophageal gland cells of M. incognita. RT-PCR analysis confirmed that their transcript abundances were high in the early parasitic juvenile stages, and low (Mi-cm-1) or undetectable (Mi-cm-2) in later parasitic stages of the nematode. Southern blot analysis revealed that these CM genes were members of a small multigene family in Meloidogyne species. The widespread presence of CMs in the specialized sedentary endoparasitic nematode species suggests that this multifunctional enzyme may be a key factor in modulating plant parasitism.