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Functional Screening Yields a New β-1,4-Endoglucanase Gene from Heterodera glycines that May be the Product of Recent Gene Duplication

January 2001 , Volume 14 , Number  1
Pages  63 - 71

Yitang Yan , 1 Geert Smant , 2 and Eric Davis 1

1Department of Plant Pathology, Box 7616, North Carolina State University, Raleigh 27695, U.S.A.; 2Department of Nematology, Wageningen University and Research Center, Binnenhaven 10, 6709 PD Wageningen, The Netherlands

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Accepted 2 October 2000.

Clones with secreted cellulolytic activity were identified when a cDNA library constructed from poly A(+) RNA of preparasitic second-stage juveniles of Heterodera glycines, the soybean cyst nematode, was expressed in the Escherichia coli SOLR strain and overlaid with a carboxymethylcellulose (CMC) substrate. Twenty CMC-degrading clones were analyzed, and all were either identical or strongly similar to a β-1,4-endoglucanase gene (HG-eng-2), previously isolated from H. glycines. A subgroup of identical “HG-eng-2-like” clones had considerable differences in the 5′ untranslated region compared with HG-eng-2 and were designated HG-eng-3. One H. glycines genomic clone contained HG-eng-2 and HG-eng-3 full-length genes, separated by a distance of approximately 8 kb, and a second genomic clone contained two copies of HG-eng-2, separated by approximately 6.5 kb, suggesting the presence of endoglucanase gene clusters in H. glycines. The HG-eng-2 and HG-eng-3 genes were in opposite transcriptional orientation, with considerable nucleotide differences in their 5′ flanking regions. The highly conserved nucleotide sequence in the introns and exons and their close proximity within the genome suggest that HG-eng-2 and HG-eng-3 are the products of recent gene duplication and inversion.

Additional keywords: cellulase, evolution, parasitism, pathogenesis, plant-parasitic nematode.

© 2001 The American Phytopathological Society