2024-B6 Can a tree remember a drought? Understanding the mechanisms of tree memory

Overview

Trees are long living, sessile organisms that represent a fundamental component of most of earth ecosystems. Being immobile during their life, trees need to efficiently adapt to changes of environment and to stresses, in order to reach maturity and reproduction. However, contrary to animals, trees do not rely on a learning strategy based on a central-nervous apparatus, and the existence of certain form of adaptive memory in these organisms is debated.  

Recent advanced in genomics studies are always more convincingly showing that environmental information can be recorded at molecular level on DNA through epigenetic marks. Epigenetics studies molecular changes of DNA (mostly DNA methylation) in response to developmental or environmental stimuli, which does not involve a change of the DNA sequence itself. These changes can be inherited during cell division and are particular stable in plants, where they represent the base of an epigenetic “memory”, which remains encoded in biological tissues and can be transmitted to progenies.  

In trees, wood is produced by plant cells that lignified and die to provide physical functions such as of mechanical support, storage and water conduction. However, part of their DNA is preserved unaltered, and retains the epigenetic information encoded in the cells in the moment they died. In temperate zones, most trees produce in their wood one growth-ring each year, so that the entire period of a tree’s life remain impressed in its wood material. As wood growth is affected by environmental conditions, trees have marks of past interactions with the environment recorded into their wood as they grow, at both physical and molecular level. However, while physical propriety of tree rings is well investigated, the possible epigenetic changes associated to the residual DNA in different rings re.  

This project aims to understand how trees use environmental information to adapt to a changing condition. This will be done by extracting DNA from different parts of tree rings and compare their epigenetic profiles. The PhD researcher will compare the DNA methylation from different tree rings and associate epigenetic changes to historical and ecological record of drought. This will allow to connect tree molecular and physical responses to the environment in in tree rings, creating for the first time a direct connection among dendrochronology, ecology and epigenetic data in trees. 

Figure 1: graphical representation of the project design. A) DNA is extracted from wood sampled at different part of a trees ring. B) the samples are sequenced and a whole genome DNA methylation profile is generated and compared. C) differences in DNA methylation are associated to historical event of drought stress.