Poster: Photosynthesis

Abs # 377: Does the CO₂/O₂ Ratio Regulate Low CO₂ Inducible Genes in Chlamydomonas reinhardtii

Presenter:	Vance, Peter , pvance@iastate.edu
Authors	Vance, Peter  (A)   Spalding, Martin H. (A)
Affiliations:	(A): Iowa State University, Botany

Under investigation is the relationship between CO₂/O₂ gas ratios and regulation of low CO₂ inducible genes related to a unique CO₂ concentrating mechanism (CCM) in a soil borne unicellular alga, Chlamydomonas reinhardtii. The CCM is part of an acclimation response to a CO₂ limited environment. Literature has previously suggested the CO₂/O₂ ratio might act as a signal for the up-regulation of low CO₂ inducible polypeptides. CO₂/O₂ ratios were manipulated in bioreactors using O₂ concentrations ranging from 21% (normal atmospheric) to 2% and realistic soil CO₂ concentrations, ranging from 5% to 0.005% (current earth atmosphere ~0.035%). Transcription of the periplasmic carbonic anhydrase gene, CAH1, was used as a reporter for regulation of low CO₂ inducible genes. Results fail to support the hypothesis that the CO₂/O₂ ratio acts as a signal for the up regulation of CAH1. The CO₂ concentration alone appears to regulate expression of CAH1 within the studied range of gas concentrations. The CO₂ concentration region where limiting CO₂ stimulates expression of CAH1 lies between 0.4% and 0.3% CO₂.