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Research article - Peer-reviewed, 2020

Transcriptional responses in developing lesions of European common ash (Fraxinus excelsior) reveal genes responding to infection by Hymenoscyphus fraxineus

Sahraei, Shadi Eshghi; Cleary, Michelle; Stenlid, Jan; Durling, Mikael Brandstrom; Elfstrand, Malin

Abstract

BackgroundWith the expanding ash dieback epidemic that has spread across the European continent, an improved functional understanding of the disease development in afflicted hosts is needed. The study investigated whether differences in necrosis extension between common ash (Fraxinus excelsior) trees with different levels of susceptibility to the fungus Hymenoscyphus fraxineus are associated with, and can be explained by, the differences in gene expression patterns. We inoculated seemingly healthy branches of each of two resistant and susceptible ash genotypes with H. fraxineus grown in a common garden.ResultsTen months after the inoculation, the length of necrosis on the resistant genotypes were shorter than on the susceptible genotypes. RNA sequencing of bark samples collected at the border of necrotic lesions and from healthy tissues distal to the lesion revealed relatively limited differences in gene expression patterns between susceptible and resistant genotypes. At the necrosis front, only 138 transcripts were differentially expressed between the genotype categories while 1082 were differentially expressed in distal, non-symptomatic tissues. Among these differentially expressed genes, several genes in the mevalonate (MVA) and iridoid pathways were found to be co-regulated, possibly indicating increased fluxes through these pathways in response to H. fraxineus.Comparison of transcriptional responses of symptomatic and non-symptomatic ash in a controlled greenhouse experiment revealed a relatively small set of genes that were differentially and concordantly expressed in both studies. This gene-set included the rate-limiting enzyme in the MVA pathway and a number of transcription factors. Furthermore, several of the concordantly expressed candidate genes show significant similarity to genes encoding players in the abscisic acid- or Jasmonate-signalling pathways.ConclusionsA set of candidate genes, concordantly expressed between field and greenhouse experiments, was identified. The candidates are associated with hormone signalling and specialized metabolite biosynthesis pathways indicating the involvement of these pathways in the response of the host to infection by H. fraxineus.

Keywords

Ash dieback; Fraxinus excelsior; HMGR1 (3-hydroxy-3-methylglutaryl-coenzyme a reductase 1); ATAF1; Resistance; Necrotic lesion

Published in

BMC Plant Biology
2020, volume: 20, number: 1, article number: 455
Publisher: BMC

Authors' information

Sahraei, Shadi Eshghi
Uppsala University
Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre
Swedish University of Agricultural Sciences, Department of Forest Mycology and Plant Pathology
Swedish University of Agricultural Sciences, Department of Forest Mycology and Plant Pathology

Associated SLU-program

SLU Network Plant Protection

UKÄ Subject classification

Botany

Publication Identifiers

DOI: https://doi.org/10.1186/s12870-020-02656-1

URI (permanent link to this page)

https://res.slu.se/id/publ/108418