Effect of temperature on pearl deposition rate and matrix protein gene expressions in Hyriopsis cumingii

Abstract

In this study, we investigated the impact of water temperature on pearl formation and the molecular mechanisms underlying this biomineralization process in the mussel Hyriopsis cumingii. In the laboratory experiment, recipient mussels received saibo grafts from donor mussels and then were cultivated at five temperatures (16, 20, 24, 28, and 32 °C) for 1 month. We found that speed of pearl formation varied with water temperature: there was no visible pearl granules at 16 and 20 °C, tawny pearl granules were collected at 24 °C and lustrous pearl granules were collected at 28 and 32 °C. The expressions of several nacreous layer matrix protein genes (hic22, hic24, HcTyr Hc-upsalin and Hcperlucin) at 28 °C and 32 °C were peaked on day 28, and the expressions of other nacreous layer matrix protein genes (hic52 and hic74) on day 28 were significant higher than day 14. In the natural environment, pearl deposition rate also increased as water temperature rose, and the optimum range for pearl growth in H. cumingii was between 28.3 and 30.3 °C. Expression of the prismatic layer-related matrix protein genes hic31 and both prismatic and nacreous layer-related matrix protein gene silkmapin was significantly high in winter, and expressions of the nacreous layer-related matrix protein genes (hic24, hic74, HcTyr, Hc-upsalin and Hcperlucin) were always higher during higher temperature seasons compared with winter. These results indicate that high water temperature can speed up pearl formation and further regulate matrix protein secretion to accelerate pearl nacre deposition.