Arabinogalactan endo-1,4-beta-galactosidase: a putative plant cell wall degrading enzyme of plant-parasitic nematodes

Plant-parasitic nematodes secrete a plethora of enzymes to degrade polysaccharides of the recalcitrant plant cell wall. Here we report on the presence of a putative endo-1,4-beta-galactosidase (EC 3.2.1.89) in cyst nematodes of the genus Heterodera. This enzyme hydrolyses beta-1,4-galactan in the hairy regions of pectin and to our knowledge it is the first report of this class of enzymes in animals. The gene was cloned from H. schachtii and subjected to a detailed molecular characterisation. The deduced protein contains a putative signal peptide for secretion, being in agreement with the presumed extracellular function of the mature protein. It has a molecular mass of 33.78 kDa and folds into an (a/beta)(8) barrel structure typical for glycosyl hydrolases. The two glutamic acids that function as electron donor and acceptor in the active site are conserved. Whole mount in situ hybridisation revealed that the gene is expressed in the subventral pharyngeal glands and the expression was correlated with the onset of parasitism