Defense priming and epigenetic mechanisms in regulating resistance against Botrytis cinerea in strawberry

Abstract

Botrytis cinerea is a necrotrophic pathogen that is reported to cause disease in more than 1400 plant species. Each year the fungi cause yield losses of great economic importance and is the most important pathogen in Norwegian strawberry production. Priming has been shown to enhance defense in plants, and epigenetic gene regulations are hypothesized to be part of the underlying mechanisms of the priming effect. Epigenetic gene regulation is mediated by specific enzymes that alter DNA or the associated histones without changing the underlying DNA sequence. In the first part of this thesis I have investigated the effect of defense priming. Plants of F. x ananassa were primed for defense by soil drenching with the chemical agent β-aminobutyric acid (BABA) and leaves were detached and drop-infected with B. cinerea. The disease development was scored phenotypically to determine if primed plants were more or less resistant to the pathogen compared to non-primed plants. After phenotypic scoring, candidate defense genes were analyzed by RT-qPCR. An enhanced susceptibility to B. cinerea was observed in the phenotypic scoring of the primed leaves compared to the non-primed leaves, and the increase in gene expression of defense related genes were mainly found to be in response to B. cinerea and not due to the priming effect of BABA. In the second part of the thesis, new constructs for CRISPR/Cas9 gene editing was made to target putative epigenetic modifiers homologous to important epigenetic modifiers in Arabidopsis thaliana to identify their role in defense against B. cinerea in F. vesca. To this end, CRISPR-vectors with different U6-promoters of F. vesca were designed and tested in a transient expression system. The vector with the highest U6-promoter-driven sgRNA-expression was then selected to knock out target genes involved in regulation of defense responses.