Regulation of XXXX formation in coccolithophores.

@entity515 @entity11588 @entity460 @entity16415 @entity505
Coccolithophores impact the ocean @entity505 cycle principally through the generation of @entity515 during @entity16415 production. Coccolithophore biomineralization has been examined most extensively in Pleurochrysis carterae and @entity11588 both of which produce mineralized scales-coccoliths-composed of elaborate calcite crystals attached to an underlying organic base plate. Calcification of preformed base plates is mediated by acidic polysaccharides and occurs in Golgi-derived structures known as mineralizing vesicles. In Pleurochrysis a high capacity @entity460 -binding polysaccharide PS2 is required for efficient nucleation of calcitic protocrystals. A galacturonomannan PS3 is required for the growth and transformation of the protocrystals into a massive double disc of calcite. The genes that regulate expression of the glycans have not yet been identified. In addition to the coccolith-bearing diploid phases, Pleurochrysis and Emiliania possess both haploid and diploid non-calcifying stages, which are self-perpetuating via binary fission. One non-calcifying Pleurochrysis phase fails to synthesis PS2 and spontaneously reverts to the mineralizing morphotype in laboratory cultures. As yet, there is little information on environmental factors that effect the expression or silencing of calcifying genes or favor the growth of calcifying over non-calcifying phases. These issues will need extensive investigation, if we are to appreciate the role of coccolithophores in the regulation of atmospheric @entity515 levels.
