Expression Profiling-Based Identification of CO2-Responsive Genes Regulated by CCM1 Controlling a Carbon-Concentrating Mechanism in Chlamydomonas reinhardtii

Photosynthetic acclimation to CO 2 -limiting stress is associated with control of genetic and physiological responses through a signal transduction pathway, followed by integrated monitoring of the environmental changes. Although several CO 2 -responsive genes have been previously isolated, genome-wide analysis has not been applied to the isolation of CO 2 -responsive genes that may function as part of a carbon-concentrating mechanism (CCM) in photosynthetic eukaryotes. By comparing expression profiles of cells grown under CO 2 -rich conditions with those of cells grown under CO 2 -limiting conditions using a cDNA membrane array containing 10,368 expressed sequence tags, 51 low-CO 2 inducible genes and 32 genes repressed by low CO 2 whose mRNA levels were changed more than 2.5-fold in Chlamydomonas reinhardtii Dangeard were detected. The fact that the induction of almost all low-CO 2 inducible genes was impaired in the ccm1 mutant suggests that CCM1 is a master regulator of CCM through putative low-CO 2 signal transduction pathways. Among low-CO 2 inducible genes, two novel genes, LciA and LciB, were identified, which may be involved in inorganic carbon transport. Possible functions of low-CO 2 inducible and/or CCM1-regulated genes are discussed in relation to the CCM.