Poster: Late and Moved Abstracts

Abs # 1440: Regulation of Chloroplast Ribosomal Proteins During Limiting CO2 Acclimation in Chlamydomonas reinhardtii

Presenter:	Wang, Yingjun , wangyj@iastate.edu
Authors	Wang, Yingjun  (A)   Spalding, Martin H (A)
Affiliations:	(A): Iowa State University

The inducible CO2 concentrating mechanism (CCM) of microalgae represents an adaptation whereby a microalga can acclimate its metabolism to changes in its external environment. During limiting CO2 acclimation in Chlamydomonas, several genes have been demonstrated to be under either up- or down-regulation at the level of transcript abundance. Here, we report down-regulation of genes encoding chloroplast ribosomal proteins upon exposure of cells to limiting CO2 concentrations. The transcript of a gene encoding a homologue of E. coli ribosomal protein L7/L12 decreased in abundance when cells were transferred from high CO2 (5%) to low CO2 (350ppm) or very low CO2 (100ppm and 50ppm) in wild-type Chlamydomonas but not in cia5, a mutant with a defect in an element regulating CO2 responses. The extent of the decrease in message abundance was inversely correlated with the CO2 concentration. In 350ppm or 100ppm CO2, the decrease in transcript abundance was transient, showing either a full (350 ppm CO2) or a partial (100 ppm CO2) recovery after 12 hours. However, in a mutant, pmp1, with a deficiency in accumulation of internal Ci, the decrease in transcript abundance did not recover significantly. The regulation by CO2 concentration of genes encoding chloroplast ribosomal protein subunits will be discussed with regard to potential signals and potential roles in the acclimation process.