Active Last updated: 29.04.2019
End: jan 2020
Start: apr 2016

The spruce bark beetle (Ips typographus) has caused great economic and ecological losses in Norwegian spruce forests. Warming temperatures are predicted to cause an increase in the frequency of bark beetle attacks. Recent work has shown that treating spruce trees with a naturally produced tree hormone, methyl jasmonate, helps the trees defend themselves against spruce bark beetle attacks. This treatment is similar to a person getting a vaccination. When painted with methyl jasmonate, a tree builds up defenses which can be rapidly deployed when the tree is under attack. This initial increase in ability to respond to attack can last for weeks or months. In this project, we are seeking to understand the changes that occur at the cellular and molecular level to make possible this rapid response. In addition, methyl jasmonate treatment produces new "memories" for the tree. These "memories" are stored as changes to the tree's DNA and allow the tree to continue to have heightened defense responses for months or even years. This process is called "defense priming". In this project, we will explore how these DNA "memories" are made. We are also interested to see if these "memories" can be passed on to the offspring of treated trees. If so, we may be able to help protect the next generation of forests from increased bark beetle attack by immunizing their parents with methyl jasmonate. So far we have learned that increasing ability to produce enzymes that breakdown fungal cell walls is one of the important memories stored after methyl jasmonate treatment.

Status Active
Start - end date 15.04.2016 - 01.01.2020
Project manager Melissa Magerøy
Division Division of Biotechnology and Plant Health
Department Molecular Plant Biology
Total budget 7947000

Publications in the project

To document

Abstract

Plants are sessile organisms that lack a specialized immune system to cope with biotic and abiotic stress. Instead, plants have complex regulatory networks that determine the appropriate distribution of resources between the developmental and the defense programs. In the last years, epigenetic regulation of repeats and gene expression has evolved as an important player in the transcriptional regulation of stress‐related genes. Here, we review the current knowledge about how different stresses interact with different levels of epigenetic control of the genome. Moreover, we analyze the different examples of transgenerational epigenetic inheritance and connect them with the known features of genome epigenetic regulation. Although yet to be explored, the interplay between epigenetics and stress resistance seems to be a relevant and dynamic player of the interaction of plants with their environments.

Abstract

Bark beetles and their symbiotic bluestain fungi kill more trees than all other natural factors and cause great economic losses in Norway spruce and other conifers. The tree's natural defenses are the most important factor maintaining bark beetle-fungus complexes at low, endemic levels. Spraying Norway spruce trees with the plant hormone methyl jasmonate (MeJA) primes tree defenses without eliciting notable induced defenses, but enables the trees to respond much more quickly and strongly when challenged by bark beetles or fungi several weeks after treatment. This phenomenon, known as defense priming, is a form of acquired resistance that enables cost-effective and vigorous defense responses. In field experiments with 50-year-old clonal spruce trees terpene concentrations in the bark increased 60-fold within 24 h after mechanical wounding of MeJA primed trees, compared with a 13-fold increase in unprimed control trees. We also observed altered transcriptional patterns in primed trees using Illumina deep transcriptome sequencing. When wounded, primed trees launched vigorous induced defenses with significant differential regulation of gene transcripts, such as those involved in phenylpropanoid synthesis leading to lignification. Resistance-like genes, such as the NB-LRR coding genes, are also more rapidly induced in primed than in unprimed trees. Transcriptome results from primed but unwounded trees indicate an alteration in the state of the chromatin, resembling changes associated with the activity of the epigenetic machinery creating long-lasting epigenetic marks. We do not know yet how long the primed state is activated in Norway spruce, but our data so far indicate that it may last for at least 3 years.