Identification of the C1q gene family and characterization of its transcriptional responses to low-temperature stress and Vibrio parahaemolyticus challenge in the noble scallop Chlamys nobilis.

C1q, a pivotal pattern recognition receptor (PRR) in the innate immune system, plays crucial roles in the defense of aquatic invertebrates against environmental stressors and pathogen infections. However, systematic identification and functional characterization of the C1q gene family in bivalves remain largely unexplored. In this study, leveraging thegenomic and transcriptomic analysis of the noble scallop Chlamys nobilis, we identified a total of 22 C1q family genes, comprising 9 classical C1q genes (designated CnC1q) and 13 C1q tumor necrosis factor-related protein genes (designated CnC1qtnf). Comprehensive analyses of physicochemical properties, conserved domains, and phylogenetic relationshipsdemonstrated that C1q genes are evolutionarily conserved across bivalve species. Comparative genomic analysisdemonstrated that C. nobilis harbors an expanded repertoire of C1q genes relative to other scallop species. Tissue-specific transcriptomic profiling demonstrated that CnC1q and CnC1qtnf genes exhibit distinct tissue-specific expression patterns, with the majority displaying significantly elevated expression in immune-related tissues, including gill, hemolymph, and kidney. Time-course expression analysis under low-temperature stress (9 °C) demonstrated that all C1q genes were differentially expressed during the 6-48 h post-stress period, with the majority exhibiting a sustained upregulation pattern. Furthermore, following 48 h of V. parahaemolyticus challenge, CnC1qBb was significantly upregulated. Overall these findings collectively indicate that the C1q gene family plays pleiotropic roles in low-temperature adaptation and antibacterial immunity in C. nobilis. Collectively, this study provides valuable insights into the immune functions of bivalve C1q genes and establishes a theoretical framework for the genetic improvement of stress resistance in C. nobilis aquaculture.