De novo transcriptome assembly and discovery of drought-responsive genes in eastern white spruce (Picea glauca)

Forests face an escalating threat from the increasing frequency of extreme
drought events driven by climate change. To address this challenge, it is
crucial to understand how widely distributed species of economic or
ecological importance may respond to drought stress. Here, we used
RNA-sequencing to investigate transcriptome responses at increasing levels
of water stress in white spruce (Picea glauca (Moench) Voss), distributed
across North America. We began by generating an expanded transcriptome
assembly emphasizing short-term drought stress at different developmental
stages. We also analyzed differential gene expression at four time points
over 22 days in a controlled drought stress experiment involving
2-year-old plants and three genetically unrelated clones. De novo
transcriptome assembly and gene expression analysis revealed a total of
33,287 transcripts (18,934 annotated unique genes), with 4,425 unique
drought-responsive genes. Many transcripts that had predicted functions
associated with photosynthesis, cell wall organization, and water
transport were down-regulated under drought conditions, while transcripts
linked to abscisic acid response and defense response were up-regulated.
Our study highlights a previously uncharacterized effect of drought stress
on lipid metabolism genes in conifers and significant changes in the
expression of several transcription factors, suggesting a regulatory
response potentially linked to drought response or acclimation. Our
research represents a fundamental step in unraveling the molecular
mechanisms underlying short-term drought responses in white spruce
seedlings. In addition, it provides a valuable source of new genetic data
that could contribute to genetic selection strategies aimed at enhancing
the drought resistance and resilience of white spruce to changing
climates.