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Analysis of microbiomes and metatranscriptome of Norway spruce trees naturally infected by the conifer pathogen Heterobasidion sp.

Fred Asiegbu: University of Helsinki

<div>Microbiomes associated to crops and forest trees are critical to forestry, agriculture and global food security. Despite significant progress achieved in our understanding of the composition of microbial communities associated with plants, very little is known about the effect of plant pathogens on their structure particularly the least studied forest trees. We investigated the effect of <em>Heterobasidion </em>root rot disease on microbial communities associated with Norway spruce. The sequenced 16S and ITS2 data were analyzed using the mothur operation pipeline. Canonical analysis of principle coordinate (CAP) and principal coordinates analysis (PCoA) were used to visualize the microbial community structure. To identify <em>in-planta</em> expressed pathogen genes, the processed RNA-seq data were mapped against genome of Spruce and <em>Heterobasidion</em> respectively. Results showed that diseased and asymptomatic trees significantly differed in the structure of the microbiome communities residing in their sapwood. Furthermore, inspite of considerable overlap in shared microbiota, metatranscriptomic analysis revealed pronounced differences in gene expression pattern among the individual symptomatic and asymptomatic trees. The distance-based linear model analysis showed that expression levels of several genes with a role in host defense were significantly correlated with the abundance of <em>in planta</em> expressed pathogen transcripts. Our results further provides a baseline for a functional understanding of the dynamics of the microbiome community of conifer trees.</div>