Isolation of a cDNA Encoding a β-1,4-endoglucanase in the Root-Knot Nematode Meloidogyne incognita and Expression Analysis During Plant Parasitism

A beta-1,4-endoglucanase encoding cDNA (EGases, E.C. 3.2.1.4), named Mi-eng-1, was cloned from Meloidogyne incognita second-stage juveniles (J2). The deduced amino acid sequence contains a catalytic domain and a cellulose-binding domain separated by a linker. In M. incognita, the gene is transcribed in the migratory J2, in males, and in the sedentary adult females. In pre-parasitic J2, endoglucanase transcripts are located in the cytoplasm of the subventral esophageal glands. The presence of beta-1,4-endoglucanase transcripts in adult females could be related to the expression of the gene in esophageal glands at this stage. However, cellulase activity within the egg matrix of adult females suggests that the endoglucanase may also be synthesized in the rectal glands and involved in the extrusion of the eggs onto the root surface. The maximum identity of the predicted MI-ENG-1 catalytic domain with the recently cloned cyst nematode beta-1,4-endoglucanases is 52.5%. In contrast to cyst nematodes, M. incognita pre-parasitic J2 were not found to express a beta-1,4-endoglucanase devoid of a cellulose-binding domain.