The carbonic anhydrase isoforms of Chlamydomonas reinhardtii: intracellular location, expression, and physiological roles

Abstract

Aquatic photosynthetic organisms, such as the green alga Chlamydomonas reinhardtii, respond to low CO(2) conditions by inducing a CO(2) concentrating mechanism (CCM). Carbonic anhydrases (CAs) are important components of the CCM. CAs are zinc-containing metalloenzymes that catalyze the reversible interconversion of CO(2) and HCO(3)(-). In C. reinhardtii, there are at least 12 genes that encode CA isoforms, including three alpha, six beta, and three gamma or gamma-like CAs. The expression of the three alpha and six beta genes has been measured from cells grown on elevated CO(2) (having no active CCM) versus cells growing on low levels of CO(2) (with an active CCM) using northern blots, differential hybridization to DNA chips and quantitative RT-PCR. Recent RNA-seq profiles add to our knowledge of the expression of all of the CA genes. In addition, protein content for some of the CA isoforms was estimated using antibodies corresponding to the specific CA isoforms: CAH1/2, CAH3, CAH4/5, CAH6, and CAH7. The intracellular location of each of the CA isoforms was elucidated using immunolocalization and cell fractionation techniques. Combining these results with previous studies using CA mutant strains, we will discuss possible physiological roles of the CA isoforms concentrating on how these CAs might contribute to the acquisition and retention of CO(2) in C. reinhardtii.

Acclimation to Very Low CO2: Contribution of Limiting CO2 Inducible Proteins, LCIB and LCIA, to Inorganic Carbon Uptake in Chlamydomonas reinhardtii

“…LCIB, located around the pyrenoid, traps CO 2 , either escaping from the pyrenoid or entering from outside the cell, into the stromal HCO 3 2 pool. This stromal HCO 3 2 pool then provides substrate to the pyrenoid thylakoid tubules for CAH3-catalyzed dehydration to CO 2 for Rubisco, as described in previous CCM models (Spalding et al, 1983b;Mitra et al, 2005;Spalding, 2008;Moroney et al, 2011).…”

“…Genetic analysis of LCIB/CAH3 double mutants indicated that LCIB functions downstream of CAH3, a thylakoid lumen CA (Duanmu et al, 2009b). Because CAH3 catalyzes dehydration of accumulated HCO 3 2 to provide CO 2 for Rubisco inside the pyrenoid (Spalding et al, 1983b;Moroney et al, 2011), it has been hypothesized that LCIB captures CO 2 leaked from the pyrenoid, possibly by unidirectionally hydrating CO 2 back to HCO 3 2 (Duanmu et al, 2009b). If this hypothesis is correct, it also implies that LCIB may also function in active Ci accumulation by unidirectionally hydrating externally diffused CO 2 into the stromal HCO 3 2 pool (Wang and Spalding, 2014).…”

Transcriptome-Wide Changes in Chlamydomonas reinhardtii Gene Expression Regulated by Carbon Dioxide and the CO2-Concentrating Mechanism Regulator CIA5/CCM1

“…Internal accumulation of C i occurs against a large concentration gradient, so accumulation must occur as HCO 3 2 because its permeability across lipid membranes is 1000-fold lower than that of CO 2 . However, Rubisco uses CO 2 as substrate, so, along with C i transporters, carbonic anhydrases (CAs), which catalyze interconversion of CO 2 and HCO 3 2 , also play important roles in the CCM, (Spalding et al, 1983a;Coleman and Grossman, 1984;Moroney et al, 2011).…”

Cloning of SjCA gene and its expression analysis on upland cottons

“…α-, β-, and γ-CA have been reported to be distributed widely in microalgae and higher plants, are zinc-metalloenzymes that catalyze the reversible interconversion of CO 2 and HCO 3¯ [29] . In higher plants, CAs play a vital role in the process of photosynthesis, respiration, ion absorption [30] .…”