Developmental expression of secretory B-1,4-endoglucanases in the subventral esophageal glands of Heterodera glycines

Jan M. de Boer(1), Yitang Yan(2), Xiaohong Wang(2), Geert Smant(3), Richard S. Hussey(4), Eric L. Davis(2), and Thomas J. Baum(1).

1 Department of Plant Pathology, Iowa State University, 351 Bessey Hall, Ames, IA 50011.

2 Department of Plant Pathology, North Carolina State University, 1515 Gardner Hall, Raleigh, NC 27695.

3 Laboratory for Nematology, Wageningen Agricultural University, Binnenhaven 10, 6709 PD Wageningen, The Netherlands.

4 Department of Plant Pathology, University of Georgia, Athens, GA 30602-7274.

Corresponding author: J.M. de Boer

E-mail: jmdeboer@iastate.edu

Abstract

Two B-1,4-endoglucanases (EGases), Hg-eng-1 and Hg-eng-2, were recently cloned from the soybean cyst nematode, Heterodera glycines, and their expression was shown in the subventral esophageal glands of hatched second-stage juveniles (J2). We examined the expression of these EGases in the subventral glands of all post-embryonic life stages of H. glycines using in situ hybridization and immunolocalization. The first detectable accumulation of EGase mRNAs occured in the subventral glands of unhatched J2. EGase transcripts remained detectable in J2 after hatching and during subsequent root invasion. However, in late parasitic J2 and third-stage juveniles (J3), the percentage of individuals that showed EGase transcripts decreased. In female fourth-stage juveniles and adult females, EGase transcripts were no longer detected in the subventral glands. EGase hybridization signal reappeared in unhatched males coiled within the J3 cuticle, and transcripts were also present in the subventral glands of migratory adult males. Immunofluorescence labeling showed that EGase translation products are most abundantly present in the subventral glands of preparasitic J2, migratory parasitic J2, and adult males. The presence of EGases predominantly in the migratory stages suggests that the enzymes are used by the nematodes to soften the walls of root cells during penetration and intracellular migration.