Epigenetic contribution to phenotypic plasticity and biotic stress-induced memory in Populus nigra

In long-lived sessile organisms such as trees, phenotypic plasticity is an important requirement for successful persistence in changing or variable environments. In this sense, epigenetic mechanisms have the potential to mediate long-term plastic responses to environmental change. Part of this adaptive plasticity occurs almost immediately after new stress exposure, through coordinated modulation of gene expression associated with the epigenetic machinery (DNA methylation, histone modifications and/or small RNA interference). More important, these epigenetic marks can be long-lasting and sometimes heritable without a change in the DNA sequence. Long-lasting mechanisms for environmental responses may be of particular relevance to long-lived species such as trees, however the specific epigenetic mechanisms of phenotypic plasticity are still far from completely understood. In this project, we will focus on a clonal tree species, Populus nigra Italica, which has been distributed via planted cuttings across Europe since the 18th century. The low genetic variation in a single and geographically widespread clonal lineage gives way to studying phenotypic plasticity being explained mostly by epigenetic related mechanisms. Moreover, many poplar plantations regularly suffer from severe infections by biotrophic rust fungi Melampsora larici-populina. However, until now, studies have focused only on the first infection cycle and posterior responses/interactions are still unknown. The main aims of the present research project are to (1) identify genomic regions
associated with stress-induced epigenetic modifications and their functional consequences, (2) evaluate the temporal methylation stability of such loci, and (3) explore the interplay of epigenetic mechanisms involved in plant-pathogen interaction.