Transcriptional acclimation and spatial differentiation characterize drought response by the ectomycorrhizal fungus Suillus pungens

Changing precipitation regimes are a challenge for forest health under
future climate scenarios. If belowground symbionts can acclimate to
changing moisture regimes it may buffer forest trees from these changes.
In this study we exposed the ectomycorrhizal fungus Suillus
pungens to acute and chronic drought stress and used RNASeq of
both ectomycorrhizal roots and extraradical mycelium to gauge the
magnitude of stress, identify key genes involved in drought response, and
gauge potential ecosystem consequences of drought. We found that there
were major transcriptional differences for S. pungens in
ectomycorrhizal roots (28% of genes) and extraradical mycelium (41% of
genes) under acute drought stress, but only 0.1-2% of genes were
differentially expressed in chronic drought treatments. Up to 56% of
differentially expressed genes under acute drought were unique to either
roots or mycelium. While a number of implicated genes, such as those
encoding for trehalose, have well-known roles in osmotic stress, others,
such as fungal hydrophobins and atromentin, have received less study and
may also impact other ecosystem functions. These results suggest that
functional compartmentalization is key to ectomycorrhizal fungal
adaptation to stressful climatic conditions and there is high potential
for fungal acclimation to ameliorate future climate
stress.