The involvement of a novel calmodulin-like protein isoform from oyster Crassostrea gigas in transcription factor regulation provides new insight into acclimation to ocean acidification

•A novel CgCaLP-2 gene was identified in Crassostrea gigas and it underwent alternative splicing.•Two protein isoforms were detected and the 23 kD form mainly responded to long-term CO2 exposure.•CgCaLP-2 redistributed to nuclear membrane after long-term CO2 exposure.•The expression of a transcription factor CgSIX4 was associated with CgCaLP-2 under CO2 exposure and in vivo knock down further verified their relevance.