Adaptive Gene-Environment Associations in Populus flowering Time Genes: New Insights from the Southern Range Edge of Balsam Poplar

Discovering genomic regions conferring local adaptation is a key priority in forest tree genomics to ensure optimal breeding of adapted germplasm and the conservation of forest genetic resources under climate change. Here, we report on adaptive gene-environment associations among 27 genes in the Populus flowering time gene network, analyzed on a range-wide collection of >1000 balsam poplar clones, including dense sampling of the southern range edge. We employ a series of novel computational techniques (Generalized Dissimilarity Modeling and Gradient Forests) that model multivariate environment associations in Populus flowering time genes and estimate non-linear turnover functions of adaptive SNPs along climate gradients. Flowering time genes in balsam poplar show extensive climate adaptation, the most pronounced of which is a strong threshold responses to summer temperatures. Predicted disruption of the gene-environment relationship under future climate scenarios suggests that range edge populations may harbor unique genomic resources for breeding climate adapted germplasm for the future.