Proline metabolism and its osmotic regulatory role in enhancing hypersalinity tolerance of the razor clam (Sinonovacula constricta)

Abstract

Proline serves as an important osmolyte in maintaining osmotic pressure and stabilizing cellular structure in aquatic organisms, and is essential for adaptation to salinity stress. This study focuses on the razor clam (Sinonovacula constricta), and investigated the metabolism and synthesis of proline in response to changing salinity. The proline content in gill tissues of razor clams significantly increased over time and with different levels of salinity exposure. The key genes involved in proline metabolism, including (Aminotransferase (ScOAT), Δ1-pyrroline-5-carboxylic acid synthase (ScP5CS), and proline dehydrogenase (ScProDH) were investigated, as well as enzyme activities associated with these genes in razor clams. The expression and activity of P5CS increased significantly under hypersalinity conditions, whereas that of OAT enzyme activity decreased. This suggested that the glutamate pathway had an important role in the proline synthesis during hypersalinity. ProDH activity was negatively correlated with salinity and regulated by the proline content, indicating a significant role of ProDH in proline accumulation under hypersalinity conditions. ScP5CS was heterologously expressed in yeast Saccharomyces cerevisiae, followed by exogenous proline supplementation studies. Recombinant S. cerevisiae incubated with ScP5CS exhibited elevated levels of proline, with the growth performance of recombinant strain surpassing that of the control group after salinity stress. In addition, razor clams exposed to exogenous proline under high salinity conditions showed expedite osmotic regulation, whereby the hemolymph pressure reached equilibrium more quickly. Together, these results indicated that the proline content increased under high salinity, which could improve the tolerance of razor clams to hypersalinity, offering novel perspectives into molecular mechanism of salinity adaptation in shellfish.