A naturally synonymous mutation modulates an ERK-centered regulatory network to mediate thermotolerance divergence in Crassostrea oysters.

Kinase-mediated phosphorylation is crucial for thermal adaptation. While extracellular signal-regulated kinase 1/2 (ERK1/2) signaling is well characterized in model organisms, its functional divergence and genetic regulation in marine species with distinct thermal adaptations remain poorly understood. In this study, we investigated the genetic basis of differential ERK activation under heat stress using two oyster subspecies from distinct thermal niches: Crassostrea gigas and Crassostrea angulata. Combining ERK inhibition assays with heat stress treatments, followed by proteomic and phosphoproteomic profiling, we constructed a heat-responsive ERK network and identified that ERK phosphorylates ATP-dependent 6-phosphofructokinase (PFK) at Thr775, enhancing its enzymatic activity and glycolytic capacity. Genome-wide association analysis further revealed that a synonymous mutation in the leucine-rich repeat protein SHOC2 drives divergent ERK phosphorylation patterns between the two subspecies by altering RNA structure and expression. Our findings demonstrated that the heat-responsive SHOC2-BRAF-ERK-PFK cascade exhibits stronger activation in thermotolerant species, enabling marine ectotherms to fine-tune metabolic responses to temperature variation. This study serves as an experimental case elucidating how genetic variations shape thermal adaptation divergence through phosphorylation-mediated regulation, thereby providing a molecular framework for adaptive mechanisms of climate variability.