SUMMARY The soybean
cyst nematode, Heterodera glycines, produces beta-1,4-endoglucanases (
cellulases) that are secreted during
infection of soybean. The gene structures of three, hg-eng-4, hg-eng-5 and hg-eng-6, of the six beta-1,4-endoglucanase genes, all family 5 glycosyl
hydrolases previously identified from H. glycines, are presented here. Furthermore, we present the detailed expression analyses of beta-1,4-endoglucanase genes as well as the biochemical properties of four H. glycines
endoglucanase enzymes. Two of the endoglucanases, HG-ENG-5 and HG-ENG-6, differed significantly in their amino acid sequence of the catalytic domains and their gene structure from that of the other four beta-1,4-endoglucanases. Quantitative real-time RT-PCR revealed distinct developmental expression differences among the hg-eng family members during the early stages of parasitism and relatively low expression levels in late parasitic stages, with the exception of the adult male stage for some eng genes. Recombinant HG-ENGs degraded
carboxymethylcellulose and optimum
enzyme activity ranged from pH 5.5 for HG-ENG-5 to pH 8 for HG-ENG-6.
EDTA, Ca(2+), Co(2+), Mg(2+) and Fe(2+) did not affect
enzyme activity of any ENG
protein, whereas Zn(2+), Cu(2+) and Mn(2+) inhibited
enzyme activity from 23% to 73% in some cases. In tests with 12 different
polysaccharide substrates,
enzyme activity was restricted to beta-1,4 linkages with all ENG
proteins tested. Only HG-ENG-5 and HG-ENG-6 had relatively high activity on
xylan and slightly degraded
microcrystalline cellulose. Together, these data reveal distinct differences in expression and biochemistry of
cyst nematode parasitism genes and
proteins, respectively, and cast light on the intricate interactions between a parasitic animal and its plant host.