S14 - Session P6 - Fungal ethylene biosynthesis in the Verticillium dahliae-sweet pepper interaction

Authors: Shirley Marcou *, Monica Höfte, Lien Tyvaert, Thomas Depaepe, Dominique Van Der Straeten, Siel Goethals

Vascular pathogens such as Verticillium species are a serious threat worldwide and cause wilting in a broad range of horticultural plants. Verticillium dahliae is, among all Verticillium species, the most notorious species inducing enormous crop losses in many hosts, including Capsicum annuum L. (sweet pepper). Despite the low content of nutrients in the xylem sap, V. dahliae is able to survive and even flourish in such a nutrient-poor environment. We hypothesize that V. dahliae has developed divergent mechanisms to increase the amount of nutrients in the xylem. The V. dahliae /sweet pepper pathosystem was used as a model to investigate a possible link between fungal ethylene production and nutrient content in the xylem. We have studied the different pathways by which V. dahliae can produce ethylene and investigated the influence of nutrient stress on expression of ethylene biosynthesis genes and ethylene production. The in planta expression of fungal ethylene biosynthesis genes and the effect of the pathogen on the plant ACC synthases was also assessed. We discovered that V. dahliae is able to produce ethylene via three different pathways and can use ACC, methionine, and 2-oxoglutarate and arginine as precursors. Our results suggest that pathways involved in ethylene biosynthesis and ACC metabolism are activated in nutrient-limiting conditions to increase nutrient availability for V. dahliae and that ethylene is produced as a byproduct. Both the fungal ACC-dependent pathway and the ethylene pathway (via EFE) -which uses 2-oxoglutarate as precursor- are expressed in planta . The EFE gene was strongly expressed in both roots and shoots. We are currently constructing fungal EFE-mutants to unravel the role of this highly expressed fungal ethylene gene in planta .