The Mechanism of Glycine Betaine Mediated Cellular Osmoregulation-Revision 2

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Pierce 9604679 This proposal requests funds to continue a study of the mechanisms that regulate the concentration of the intracellular osmolyte, glycine betaine, in response to high salinity stress. Glycine betaine is an extremely common and important osmolyte in a wide variety of species ranging from bacteria to plants and animals. Although a great deal is known about the salinity-induced regulation of glycine betaine in bacteria, far less is known about its regulation in plants, and even less in animals. The PI had found previously that oysters (Crassostrea virginica) from the Atlantic coast utilize substantial amounts of glycine betaine to regulate intracellular osmotic concentrations following high salinity stress. Conspecific oysters from the Chesapeake Bay have much smaller levels of glycine betaine that do not change following salinity stress and the Bay oysters are not as salinity tolerant. In addition, the PI's previous work has indicated that the basis of this difference in glycine betaine accumulation and salinity tolerance lies within synthetic pathways that reside in the mitochondria. Furthermore, in bacteria and plants, salinity-induced glycine betaine accumulation is regulated by a family of genes that is osmotically-activated. Almost nothing is known about osmotically activated genes in animals. The experiments described in this project propose to exploit the differences between Atlantic and Bay oysters in glycine betaine metabolism to begin to understand how this important, but scarcely studied osmolyte is regulated in animals cells. Further, since all of the Bay oysters are parasitized by the haplosporidian parasite, Perkinsus marinas, which has devastated the Bay oyster fishery, the initial experiments will focus on the possibility that the parasite is causing the biochemical differences between the two oyster groups. The results will contribute a great deal to the understanding of glycine betaine regulation, salinity tolerance mechanis ms, cellular osmoregulation and, perhaps, uncover some of the biochemical consequences of that parasite on oyster metabolism.