Comparative Analysis of Heat Exposure-Induced Molecular Changes in Two Turtle Species with Contrasting Thermal Adaptations.

Global climate change has heightened heat stress, threatening amphibian and reptile survival, including turtles. Although turtle species vary in heat tolerance, the molecular mechanisms behind these differences are not well understood. This study aimed to identify differentially expressed genes (DEGs) in response to heat stress (32°C) versus normal temperature (25°C) in eight tissues (brain, heart, intestine, liver, lung, muscle, spleen, and stomach) of two turtle species: Platysternon megacephalum (low heat tolerance) and Trachemys scripta elegans (high heat tolerance) using RNA-seq. The results revealed significant down-regulation of genes involved in energy and lipid metabolism in P. megacephalum, suggesting metabolic suppression under heat stress. Furthermore, the jumonji and AT-rich interaction domain containing 2 (JARID2) gene, which regulates cell proliferation and differentiation, was up-regulated in all tissues of P. megacephalum but down-regulated in all tissues of T. scripta elegans under heat stress. Pathway analysis revealed that protein processing in the endoplasmic reticulum was significantly enriched in brain, heart, lung, and muscle tissues of P. megacephalum, with BiP, CHOP, NEF, and HSPs significantly up-regulated in brain tissue, highlighting this pathway's impact on heat stress response. Seven hub genes were identified in the protein processing in the endoplasmic reticulum pathway in P. megacephalum. In contrast, T. scripta elegans showed a moderate response, with up-regulation of ribosomal genes in the brain to enhance protein synthesis and folding, while down-regulation of cell cycle genes in the intestine helped conserve energy for cellular repair. No significant pathways were found in other tissues of T. scripta elegans. These molecular responses in T. scripta elegans likely contribute to its better adaptation to heat stress. This study provides new insights into the molecular mechanisms of heat stress adaptation in turtles, offering valuable knowledge for understanding their ability to cope with future climate change.