Glucanase-Induced Stipe Wall Extension Shows Distinct Differences from Chitinase-Induced Stipe Wall Extension of Coprinopsis cinerea

Abstract

This study reports that a high concentration of the endo-β-1,3-glucanase ENG (200 μg ml^-1) induced heat-inactivated stipe wall extension of <i>Coprinopsis cinerea</i>, whereas a high concentration of the extracellular β-glucosidase BGL2 (1,000 μg ml^-1) did not; however, in combination, low concentrations of ENG (25 μg ml^-1) and BGL2 (260 μg ml^-1) induced heat-inactivated stipe cell wall extension. In contrast to the previously reported chitinase-reconstituted stipe wall extension, β-1,3-glucanase-reconstituted heat-inactivated stipe cell wall extension initially exhibited a fast extension rate that quickly decreased to zero after approximately 60 min; the stipe cell wall extension induced by a high concentration of β-1,3-glucanase did not result in stipe breakage during measurement, and the inner surfaces of glucanase-reconstituted extended cell walls still remained as amorphous matrices that did not appear to have been damaged. These distinctive features of the β-1,3-glucanase-reconstituted wall extension may be because chitin chains are cross-linked not only to the nonreducing termini of the side chains and the backbones of β-1,6 branched β-1,3-glucans but also to other polysaccharides. Remarkably, a low concentration of either the β-1,3-glucanase ENG or of chitinase ChiE1 did not induce heat-inactivated stipe wall extension, but a combination of these two enzymes, each at a low concentration, showed stipe cell wall extension activity that exhibited a steady and continuous wall extension profile. Therefore, we concluded that the stipe cell wall extension is the result of the synergistic actions of glucanases and chitinases.<b>IMPORTANCE</b> We previously reported that the chitinase could induce stipe wall extension and was involved in stipe elongation growth of the mushroom <i>Coprinopsis cinerea</i> In this study, we explored that β-1,3-glucanase also induced stipe cell wall extension. Interestingly, the extension profile and extended ultra-architecture of β-1,3-glucanase-reconstituted stipe wall were different from those of chitinase-reconstituted stipe wall. However, β-1,3-glucanase cooperated with chitinase to induce stipe cell wall extension. The significance of this synergy between glucanases and chitinases is that it enables a low concentration of active enzymes to induce wall extension, and the involvement of β-1,3-glucanases is necessary for the cell wall remodeling and the addition of new β-glucans during stipe elongation growth.