| Summary: | Filter-feeding bivalves can accumulate paralytic shellfish toxins (PST) produced by toxic microalgae, which may induce oxidative stress and lipid peroxidation. Peroxisomal acyl-coenzyme A oxidases (ACOXs) are key enzymes functioning in maintaining redox and lipid homeostasis, but their roles in PST response in bivalves are less understood. Herein, a total of six and six <i>ACOX</i>s were identified in the <i>Chlamys farreri</i> and <i>Patinopecten yessoensis</i> genome, respectively, and the expansion of <i>ACOX1</i>s was observed. Gene expression analysis revealed an organ/tissue-specific expression pattern in both scallops, with all <i>ACOX</i>s being predominantly expressed in the two most toxic organs, digestive glands and kidneys. The regulation patterns of scallop <i>ACOX</i>s after exposure to different PST-producing algaes <i>Alexandrium catenella</i> (ACDH) and <i>A. minutum</i> (AM-1) were revealed. After ACDH exposure, more differentially expressed genes (DEGs) were identified in <i>C</i>. <i>farreri</i> digestive glands (three) and kidneys (five) than that in <i>P</i>. <i>yessoensis</i> (two), but the up-regulated DEGs showed similar expression patterns in both species. In <i>C</i>. <i>farreri</i>, three DEGs were found in both digestive glands and kidneys after AM-1 exposure, with two same <i>CfACOX1</i>s being acutely and chronically induced, respectively. Notably, these two <i>CfACOX1</i>s also showed different expression patterns in kidneys between ACDH (acute response) and AM-1 (chronic response) exposure. Moreover, inductive expression of <i>CfACOX</i>s after AM-1 exposure was observed in gills and mantles, and all DEGs in both tissues were up-regulated and their common DEGs exhibited both acute and chronic induction. These results indicate the involvement of scallop <i>ACOX</i>s in PST response, and their plasticity expression patterns between scallop species, among tissues, and between the exposure of different PST analogs.
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