Ribulose bisphosphate carboxylase-oxygenase (RuBPCase) is the enzyme responsible for nearly all carbon fixation on this planet and is the major carboxylating enzyme in the phytoplankton of the world's oceans. Additionally, RuBPCase may play a global role in modulating one of the greenhouse gases, CO2. Knowledge of the regulation of this enzyme is important for understanding control of primary production in the oceans and phytoplankton response to environmental perturbations or long term change. Dr. Tabita and his collaborator, Dr. Paul, will focus on the molecular regulation of this enzyme in picoplankton in coastal and oligotrophic oceanic environments. They have recently developed a method for extraction of mRNA from phytoplankton and have detected RuBPCase gene expression in natural populations. These biomolecular techniques will be used to study diel and light-dependent regulation of the RuBPCase gene in cultured Synechococcus spp. and prochlorophytes, and in natural populations. The second objective is to identify and characterize the key primary producers by amplifying RUBPCase mRNA for cloning and sequencing from natural populations. Amplification of mRNA will result in clones that originated from transcriptionally active phototrophs. Sequence data will be compared to RuBPCase data bases to identify the active species. If novel phototrophs are encountered, parsimony analysis will be performed to relate these forms to their evolutionary closest relative. In summary, the project will provide fundamental information on the control of the RuBPCase genes in response to environmental factors and identify key phototrophic organisms in oceanic picoplankton.
