A fungal endoglucanase with plant cell wall extension activity

We have identified a wall hydrolytic enzyme from Trichoderma reesei with potent ability to induce extension of heat-inactivated type I cell walls. It is a small (23-kD) endo-1,4-beta -glucanase (CeI12A) belonging to glycoside hydrolase family 12. Extension of heat-inactivated walls from cucumber (Cucumis sativus cv Burpee Pickler) hypocotyls was induced by CeI12A after a distinct lag time and was accompanied by a large increase in wall plasticity and elasticity. CeI12A also increase he rate of stress relaxation of isolated walls at very short times (< 200 ms; equivalent to reducing to, a parameter that estimates the minimum relaxation time). Similar changes in wall plasticity and elasticity were observed in wheat (Triticum aestivum cv Pennmore Winter) coleoptile (type II) walls, which showed only a negligible extension in response to CeI12A treatment. Thus, CeI12A modifies both type I and II walls, but substantial extension is found only in type I walls. CeI12A has strong, endo-glucanase activity against xyloglucan and (1 -->3,1 -->4)-beta -glucan, but did not exhibit endo-xylanase, endo-mannase, or endo-galactanase activities. In terms of kinetics of action and effects on wall rheology, wall loosening by Cel12A differs qualitatively from the action by expansins, which induce wall extension by a non-hydrolytic polymer creep mechanism. The action by CeI12A mimics some of the changes in wall rheology found after auxin-induced growth. The strategy used here to identify CeI12A could be used to identify analogous plant enzymes that cause auxin-induced changes in cell wall rheology.