Gene Expression Profiling in Eucalyptus Associates Phenylpropanoid Resistance to Teratosphaeria destructans

Teratosphaeria destructans , the causal agent of Eucalyptus leaf and shoot blight, is a highly destructive pathogen that poses a major threat to Eucalyptus plantations. Molecular mechanisms underlying resistance to T. destructans have not yet been studied. To investigate this, a transcriptome analysis was performed at 3 and 6 days post‐inoculation using leaves of a resistant genotype (GU495) inoculated with T. destructans . RNA‐sequencing and enrichment analysis revealed key metabolic processes such as the phenylpropanoid pathway associated with resistance to T. destructans . Gene expression patterns of this pathway were compared to results from a susceptible genotype, conducted in a previous study. Further analysis of GU495 genes associated with this pathway highlighted an up‐regulation of key genes coding for enzymes such as phenylalanine ammonia‐lyase 2 (PAL2), O‐methyltransferase (OMT) and cinnamate‐4‐hydroxylase (C4H), which are associated with lignin biosynthesis. Ferulic acid and chlorogenic acid are plant compounds produced through the phenylpropanoid pathway. An in vitro bioassay revealed two contrasting effects of these compounds on the germination of T. destructans . Chlorogenic acid (at 200 ppm) inhibited the germination of T. destructans completely, while ferulic acid promoted its germination. The insights provided by this study into Eucalyptus defence responses to Teratosphaeria leaf blight can be applied to structured populations to further dissect the genetic architecture underlying phenylpropanoid‐mediated resistance.