Accumulation, biotransformation and time-dependent transcriptomic responses to PSTs in scallop kidneys

As typical filter-feeding organisms, bivalve scallops exhibit strong capabilities in accumulating paralytic shellfish toxins (PSTs) from toxic algae, posing risks to public health. To investigate PST-induced molecular responses in the kidney, the major "center" for toxin transformation, a time-course transcriptome analysis of the Yesso Scallop (Patinopecten yessoensis) over six time points (0, 1, 3, 5, 10, and 15 days) after exposure to the PST-producing algae (Alexandrium catenella) were conducted. During the 15 days exposure, PST accumulation in scallop kidneys showed a continuous increase. However, the dominant toxin shifted from the low-toxicity C2 to high-toxicity neoSTX and STX compared to the algal toxin profiles. Transcriptomic analysis revealed that differentially expressed genes (DEGs) were mainly concentrated on the 3rd (629) and 10th day (745), coinciding with significant changes in toxin accumulation patterns. The SLC family was persist up-regulated throughout the exposure period, while the C-type lectin family exhibited biphasic transcriptional expression. Calmodulin was significantly up-regulated on the 15th day, the time point with the highest toxin content and toxicity. Moreover, we identified SULT4A1 as a potential key gene involved in PST biotransformation from low- to high-toxicity derivatives (neoSTX and STX), with its expression significantly associated with these toxins (Pearson's r = 0.52, 0.68). This study provides insights into the molecular mechanisms of shellfish adapt to defense phycotoxins.