Cold acclimation triggers major transcriptional changes in Drosophila suzukii

Insect life is directly depending on environment temperature. Low temperatures can alter cellular homeostasis resulting in chill damages and in most extreme cases, lethality. To counteract these deleterious effects, insects can use acclimation-related physiological adjustments. The spotted wing drosophila (SWD) Drosophila suzukii is an invasive pest of red berries. SWD is known to be chill susceptible, succumbing to cold exposures way above 0 °C. Yet, it overwinters in harsh European winter conditions, which might be partly due to its highly plastic cold tolerance. However, little is known about underlying mechanisms of cold acclimation in SWD. Here, we promoted SWD cold tolerance through increasing acclimation periods (i.e. from 2 h to 9 days) and selected the most extreme phenotype to characterize transcriptional changes by RNAseq. Significative changes were noticed in SWD cold tolerance after acclimation: the longest the acclimation period, the highest the cold tolerance. Flies acclimated for 9 days were selected for sequencing. RNAseq revealed up to 2200 significantly differentially expressed genes (1200 up- and 1000 down-regulated) compared to non-acclimated flies. Functional annotations on the up-regulated set revealed many enriched GO-terms among which transport of ions across membranes and signaling were highly represented. We also noticed upregulations of several genes involved in thermal stress resistance, like heat shock proteins and Starvin. Involvements of a cluster of genes related to ion transport in cold-hardy flies is sensible, considering that loss of ion homeostasis is the major mechanism responsible for chill-injuries. Functional annotations on the down-regulated set revealed many GO-terms related to oogenesis. This likely reflects reduced reproductive process of acclimated females. Data were validated with rt-qPCR on selected genes. Overall, these results participate to our understanding of SWD low temperature biology, a knowledge of importance for better prediction of SWD population dynamics in temperate areas.