LAUSR

The CO 2 concentrating mechanism (CCM) is a key feature of green algal cells, induced in response to limiting CO 2 conditions. Calcium-dependent signaling has been shown to play a role in this acclimation process to low inorganic carbon in Chlamydomonas reinhardtii , but the molecular players have not been characterized. One type of Ca 2+ channel, the transient receptor potential (TRP) family of ion channels is specific to the algal members of the green lineage and not found in land plants. TRP channels generally mediate the flux of Ca 2+ ions in response to environmental perturbations, and one recent study has revealed the role of Ca 2+ signaling in acclimation to limiting CO 2 in the green alga, C. reinhardtii . In this study, the gene Trp2 , encoding a Ca 2+ ion channel was identified through bioinformatics analyses as having a role in acclimation of algal cells to limiting CO 2 . Transcript abundance levels for this gene are significantly upregulated when cells are cultured in limiting CO 2 and mutant cells missing the TRP2 protein show an impaired growth phenotype. We show that a calcium binding protein CAS, is downregulated in the trp2 mutant along with other CCM genes under the control of CAS. The results suggest that the TRP2 ion channel is involved in the acclimation of C. reinhardtii cells to limiting CO 2 .