At the Institute for Biotechnology and Active Compound Research, an extensive collection of different fungal strains has been established over the last 40 years. These include species that are involved in the so called Esca syndrome of Grapevine. The wealth of natural compounds (secondary metabolites) that is produced by fungi, depends on so called gene clusters, batteries of genes that can link similar chemical building blocks in a modular and variable manner to give rise to quite different products. Of special interest are the polyketide synthases that are thought to be responsible for fungal compounds that can disrupt or modulate plant immunity and, thus, are relevant for the communication between fungi and plants. Under laboratory conditions, these gene clusters are mostly inactive. We assume, therefore that they are activated specifically in response to signals from the host plant. We are able to manipulate individual genes in these clusters, such that we can infer their function (Jacob et al., 2017). For instance, in order to dissect the effect of such plant or fungal signals, we investigate the „management level“ of certain genes, so called transcription factors (genetic switches) that are able to activate or to repress entire gene clusters.
For this purpose, we will place the regulatory sequence of these gene switches in front of a gene fragment encoding the fluorescent protein. Each time, when the switch becomes active, we will then be able to observe a green fluorescence. This allows to investigate, which signals from plant cells can activate the fungal secondary metabolism and, thus, the synthesis of natural compounds.
During a cooperation between IBWF and KIT-BOT we were already able to identify first molecular candidates for plant-fungal communication: the plant molecule ferulic acid, a precursor of lignin (the molecular base for wood) can induce in the Esca fungus Neofusicoccum parvum the formation of toxins that are possibly responsible for the symptoms of the disease.
Reference
Jacob, S., Grötsch, T., Foster, A. J., Schüffler, A., Rieger, P. H., Sandjo, L. P., ... & Thines, E. (2017). Unravelling the biosynthesis of pyriculol in the rice blast fungus Magnaporthe oryzae. Microbiology, 163(4), 541.
