Impact of sucrose transporters on fungal carbon nutrition in ectomycorrhiza

The ectomycorrhizal symbiosis enables forest ecosystems to cover about 30 % of the Earth s terrestrial surface. In this symbiosis the fungus gets easily degradable plant derived carbohydrates in exchange for nutrients. Sucrose transporters (SUTs) were long time favored to mediate sucrose efflux at the functional interface. In this work selected SUTs of Populus trichocarpa à P. deltoides were analyzed using gene expression analyses and heterologous expression in Saccharomyces cerevisiae. Manipulation of root-specific processes requires promoters causing only root-specific gene expression. The promoter of a previously identified root-specifically expressed Populus trichocarpa peroxidase gene (Potri.003G214500) was used for determination of regulatory regions responsible for the root-specific expression pattern. An in silico analysis indicated eight putative regulatory elements within a region of 1622 bp. Additionally, six truncated peroxidase promoter fragments driving GUS gene expression were examined. Two regulatory regions, one responsible for induction and one for repression of gene expression, were identified. Furthermore, a putative Alfin1 BS2 regulatory element turned out to be essential for peroxidase gene expression.