Involvement of caspase3 in the acute stress response to high temperature and elevated ammonium in stony coral Pocillopora damicornis

Apoptosis is orchestrated by a family of cysteine proteases known as the caspases, and caspase3 is the primary executioner caspase in the apoptosis. In the present study, the potential role of caspase3 was investigated under the exposure to high temperature and elevated ammonium in stony coral Pocillopora damicornis. The cDNA of a caspase3 (PdCaspase3) was identified to encode a polypeptide of 344 amino acids, and the encoded protein contained one CASc domain (Caspase, interleukin-1 beta converting enzyme homologues, from Val76 to Asn333). The recombinant protein of the mature PdCaspase3 was expressed in Escherichia coli BL21 (DE3)-Transetta, and it displayed caspase3-like activity which catalyzed the reaction of DEVD-p-nitroanilide cleavage. The expression level of PdCaspase3 mRNA increased significantly at 24 h after acute heat stress and 12 h after acute ammonium stress, reached 2.28-fold (P < 0.05) and 1.76-fold (P < 0.05) of that in the blank group, respectively. The activation level of caspase3 began to increase at 12 h (1.41-fold, P < 0.05), and reached the peak at 24 h (1.54-fold, P < 0.05) after acute heat stress. Furthermore, the activation level of caspase3 increased significantly during 6-24 h, with the highest level at 24 h (1.44-fold, P < 0.05) after acute ammonium stress. These results collectively suggested that PdCaspase3, as a homologue of caspase3, was involved in the response to high temperature and elevated ammonium, which might further regulate the symbiosis between the host and zooxanthellae in the stony coral P. damicornis.