CELL-WALL SYNTHESIS IS A MAJOR TARGET OF MYCOPARASITIC ANTAGONISM BY TRICHODERMA-HARZIANUM

We have investigated the molecular basis for the reported synergism be tween peptaibols and cell wall hydrolytic enzymes in the antagonism of phytopathogenic fungi by Trichoderma harzianum. beta-Glucan synthase activity on isolated plasma membranes of Botrytis cinerea was inhibite d in vitro by the peptaibols trichorzianin TA and TB, and this inhibit ion was reversed by the addition of phosphatidylcholine. beta-Glucan s ynthesis in vivo, assayed by the incorporation of [2-H-3]glucose into cell wall material, was inhibited by the presence of peptaibols, and t his inhibition was synergistic with exogenously added T. harzianum bet a-1,3-glucanase. This synergism is therefore explained by an inhibitio n of the membrane-bound beta-1,3-glucan synthase of the host by the pe ptaibols, which inhibit the resynthesis of cell wall beta-glucans, sus tain the disruptive action of beta-glucanases, and all together enhanc e the fungicidal activity, Therefore, we have identified cell wall tur nover as a major target of mycoparasitic antagonism.