Necrotrophic fungal plant pathogens display different mechanisms to counteract grape chitinase and thaumatin-like protein

To verify a possible absorption of TLP and chitinase by the fungal talli, mycelia were treated with β-1,3-glucanase. TLP and, to a lower extent, chitinase were released from mycelium of the three ascomycetes fungi but not from that of S. rolfsii. The treatment with β-1,3-glucanase of a mixture containing PR proteins and a purified preparation of the S. rolfsii glucan did not release TLP or chitinase. However, the two proteins were observed when the mixture was analyzed on SDS-PAGE. This result indicates a different type of binding of PR proteins with the glucan matrix of S. rolfsii in comparison to that of the three ascomycetes. As determined by RT-qPCR, one of the two examined putative glucan synthase genes of S. rolfsii was up-regulated following the administration of PR proteins, suggesting the formation of new glucan. Overall, in comparison to protease activity, the sequestering capacity of the fungal glucan matrix seems to play a major role in the fungal defense against the plant TLP and chitinase.