Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Identification of an expansin from infective juveniles of the potato cyst nematode - the first expansin outside the plant kingdom

The á- and â-expansins represent a class of plant proteins with characteristic pH-dependent in vitro cell wall-loosening and stress relaxation activity on cell walls of higher plants. Expansins, which have, until now, only been identified in land plants, induce cell wall extension within seconds and are thought to promote polymer slippage by weakening non-covalent interactions. Sequences with some degree of similarity to expansins have been found in a variety of taxa outside the plant kingdom.

However, the corresponding proteins have not yet been tested for expansin activity and therefore cannot be considered as representing functional expansins. Here we report the characterisation of a secretory protein (Gr exp-1) expressed in the esophageal glands of the plant parasitic nematode Globodera rostochiensis with both the structural and functional characteristics of a â-expansin. The structure of the Gr-exp-1 protein resembles that of plant expansins with a bacterial type cellulose-binding domain linked to a catalytic expansin domain.

The latter shows an overall sequence identity of 38% with a pistil-specific â-expansin from tobacco. Recombinant expression of Gr-exp-1 in tobacco allowed demonstration of a typical and rapid pH dependent cell wall loosening activity on heat inactivated wheat coleoptiles (a type II cell wall). The presence of â-expansin in their stylet secretions shows that these obligate plant parasites combine symbiont-independent enzymatic and non-enzymatic cell wall modifying activities to facilitate intracellular migration through plant roots.

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