Massive expansion of Hsp70 family genes in the mussel Mytilus coruscus reveals their adaptability to dynamic environments.

Heat shock protein 70 (Hsp70) is a highly conserved molecular chaperone that plays crucial roles in combating both biotic and abiotic stressors. Herein, a total of 97 Hsp70 genes distributed across nine sub-families were identified in Mytilus coruscus. Noticeable gene expansion was detected in three subfamilies, including 77 genes in Hspa12, 4 in Hspa5, and 10 in Hsp70B2. In total, 94 Mco-Hsp70 genes were unequally mapped across 12 chromosomes, with the largest gene number present on chromosome 03 (37 genes, 38.14%). Subcellular localization analysis indicated that 74 (76.3%) Hsp70s were localized in the cytoplasm, with the remaining members distributed across 8 subcellular organelles. Tandem duplication was identified as an essential driver of the expansion of Hspa5, Hsp70B2, and Hspa12 subfamily genes. Transcriptome analysis revealed that Mco-Hsp70 genes exhibited specific expression patterns across different tissues, developmental stages, and stress conditions. Notably, different Mco-Hsp70 subfamilies exhibited divergent responses to identical stimuli, and the expanded paralogs of Mco-Hspa12, Mco-Hsp70B2, and Mco-Hspa5 genes exhibited differential expression under different stress conditions. This study comprehensively explored the Mco-HSP70 gene family and elucidated transcriptional differentiation under diverse stress, enhancing our understanding of adaptation in mussels in dynamic environments.