Functional characterization of CSAD and its genomic variations modulating taurine synthesis and heat adaptation between two congeneric oyster species

Oysters are characterized by an extremely high taurine content, a feature that constitutes one of the key reasons for the nutritional and commercial value of these shellfish. Nevertheless, within these organisms, the functions of key metabolic genes and their regulatory mechanisms remain poorly understood. In the current study, we confirmed that cysteine sulfinic acid decarboxylase (CSAD) catalyzes taurine synthesis in two congeneric oyster species: the Pacific oyster Crassostrea gigas and the Portuguese oyster Crassostrea angulata. These oysters are notable for their high aquaculture yields and distinct thermal tolerance levels. Csad displayed distinct thermal response patterns in the two oyster species and significantly contributed to the enhancement of thermal tolerance. Three genomic variations in the Csad promoter region were identified. These variations enhanced the transcriptional activity by varying degrees under heat stress conditions, with the activity increasing from 2.52-fold to 3.19-fold, 2.81-fold and 4.30-fold respectively. Our findings establish Poly (ADP-ribose) polymerase 1 (PARP1) as a transcriptional coregulator mediating the species-divergent thermal response of Csad. This research fills a significant void in our understanding of the regulatory mechanisms of taurine metabolism in marine invertebrates and has the potential to lay a theoretical groundwork for the genetic improvement of oysters via molecular-based methodologies.