Cellular cold-sensing in the goldenrod gall fly, Eurosta solidaginis, involves a calcium/calmodulin signaling axis

The goldenrod gall fly, Eurosta solidaginis, overwinters as third instar larvae in the stems of goldenrod plants and is perhaps the best-studied model of freeze-tolerance among temperate species. While freezing induces a number of rapid physiological changes, the signaling mechanisms that trigger these changes are unknown. Recent studies in other species have shown that insect tissues directly respond to low temperature without nervous or hormonal input, and that calcium signaling may be involved in this process. Thus, in this study our objectives were to 1) determine whether E. solidaginis tissues are capable of cellular cold-sensing ex vivo and 2) explore the role of calcium signaling in mediating this process. Dissected tissues of E. solidaginis are indeed capable of cellular-cold-sensing ex vivo, as a 1 h gradual chilling period significantly increased the freeze-tolerance of both midgut and salivary gland tissue by ~30%. Meanwhile, using a pharmacological approach, we blocked key components of calcium signaling pathways and found that tissues were no longer capable of increasing their freeze tolerance after gradual chilling. Additionally, the activity of calcium/calmodulin dependent protein kinase II (CaMKII) was increased by freezing and during recovery from freezing, further supporting the role of calcium signaling during cold-sensing. Transcripts for both calmodulin and CaMKII were detectable in every tissue tested, suggesting that these signaling molecules can function in a general, systemic response to cold. Finally, we are currently conducting experiments using confocal live cell imaging to quantify the changes in intracellular calcium in response to low temperature.