Genes involved in the constitutive production of phenolic compounds in white spruce

Conifer forests worldwide are becoming increasingly vulnerable to the
effects of climate change. Although the production of phenolic compounds
(PCs) has been shown to be modulated by biotic and abiotic stresses, the
genetic basis underlying the variation in their constitutive production
level remains poorly documented in conifers. We used QTL mapping and
RNA-Seq to explore the complex polygenic network underlying the
constitutive production of PCs in a white spruce (Picea glauca) full-sib
family for 2 years. QTL detection was performed for nine PCs and
differentially expressed genes (DEGs) were identified between individuals
with high and low PC contents for five PCs exhibiting stable QTLs across
time. A total of 17 QTLs were detected for eight metabolites, including
one major QTL explaining up to 91.3% of the neolignan-2 variance. The
RNA-Seq analysis highlighted 50 DEGs associated with phenylpropanoid
biosynthesis, several key transcription factors, and a subset of 137 genes
showing opposite expression patterns in individuals with high levels of
the flavonoids gallocatechin and taxifolin glucoside. A total of 19 DEGs
co-localized with QTLs. Our findings represent a significant step toward
resolving the genomic architecture of PC production in spruce and
facilitate the functional characterization of genes and transcriptional
networks responsible for differences in constitutive production of PCs in
conifers.