Oral Paper

         Comparative Genomics/Transcriptomics

Transcriptomics and metabolomics in the field: analysis of flavonoid biosynthesis across a latitudinal gradient

Presenting Author
Chloe Drummond
Description
Vaccinium membranaceum Douglas ex Torr. (tall bilberry, Ericaceae) grows along a latitudinal gradient in the Pacific Northwest and the Rocky Mountain Region where grizzly bears, American black bears, ungulates and birds rely on its leaves, stems, and berries for food. Flavonoids in the leaves are important nutrients for animal wildlife, they contribute to the value of the leaf as a medicinal herb, and they are important metabolites involved in photoprotective response. Previous research shows that flavonoid content of Vaccinium leaves changes in response to light intensity and along latitudinal gradients. Latitudinal variation in Vaccinium membranaceum flavonoid content has not yet been studied using transcriptomic and metabolomic tools and may reveal latitudinal patterns in light stress response and expand our understanding of the interaction between geography and digestibility of leaves by animals. We hypothesize a greater induced flavonoid photoprotective response at higher latitudes due to longer growing season daylight length and lower temperatures that reduce photosynthetic capacity. We reason that excess light, exceeding photosynthetic capacity, can induce photoprotective responses to avoid cell damage. To test our hypothesis, we analyzed transcriptome and metabolome data from V. membranaceum leaves collected from seven populations along a latitudinal gradient, within a three-week period in August 2021. Environmental data such as soil pH and canopy cover were collected, alongside genotyping-by-sequencing data, to account for covarying effects of environment and genetic background. RNA-Seq transcriptomic data were de novo assembled and analyzed using differential gene expression analysis with gene ontology enrichment to identify flavonoid or defense-related enrichment. To identify gene expression networks correlated with latitude, the eigengene from weighted gene correlation network analysis was used in statistical regression correcting for environmental and genetic co-variables. Gene expression networks correlated with latitude were annotated with GO enrichment analysis to identify flavonoid or defense-related enrichment. LCMS untargeted metabolomic data were processed by alignment, normalization, and peak identification. Metabolites differentiating by latitude were identified using principal component analysis followed by partial least squares discriminant analysis correcting for environmental and genetic co-variables. Functions of these metabolites were annotated using the Kyoto Encyclopedia of Genes and Genomes database to identify metabolites related to flavonoid biosynthesis. Results from transcriptomic and metabolomic analysis were compared. Our study illuminates the challenges and benefits of field-based transcriptomic and metabolomic experiments. In addition, our results help to illuminate geographic patterns of abiotic stress and leaf nutrient quality. Finally, this study may serve as a foundation for understanding how this species may respond to greater UV exposure or movement to higher latitudes in the future due to climate change and inform attempts to commercially grow this species, an effort that may reduce stress of over harvesting on natural populations.