Abstract
Carbonic anhydrases (CAs) are zinc metalloenzymes that catalyze the interconversion of CO2 and HCO3− and are ubiquitous in nature. Higher plants contain three evolutionarily distinct CA families, αCAs, βCAs, and γCAs, where each family is represented by multiple isoforms in all species. Alternative splicing of CA transcripts appears common; consequently, the number of functional CA isoforms in a species may exceed the number of genes. CAs are expressed in numerous plant tissues and in different cellular locations. The most prevalent CAs are those in the chloroplast, cytosol, and mitochondria. This diversity in location is paralleled in the many physiological and biochemical roles that CAs play in plants. In this review, the number and types of CAs in C3, C4, and crassulacean acid metabolism (CAM) plants are considered, and the roles of the α and γCAs are briefly discussed. The remainder of the review focuses on plant βCAs and includes the identification of homologs between species using phylogenetic approaches, a consideration of the inter- and intracellular localization of the proteins, along with the evidence for alternative splice forms. Current understanding of βCA tissue-specific expression patterns and what controls them are reviewed, and the physiological roles for which βCAs have been implicated are presented.
Highlights
Carbonic Anhydrases Are Essential for Photosynthetic Organisms and Their Intracellular Location Is CriticalCarbonic anhydrases (CAs) play essential roles in all photosynthetic organisms
This study showed that the hydration rate of CO2 was about 58 times the photosynthetic rate. These results indicate that CA is not limiting photosynthesis in F. bidentis; the CO2 response curves of the transformants indicated that a cytosolic CA is essential for an efficient C4 concentrating mechanism (CCM) in this dicot species
Plants have many genes encoding a, b- and g-type CAs, which are found in most tissues and many intracellular compartments
Summary
Carbonic anhydrases (CAs) play essential roles in all photosynthetic organisms. In cyanobacteria, CAs located in the carboxysome are required for the conversion of accumulated HCO3À to CO2 for fixation by ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) (Espie and Kimber, 2011). The specific expression patterns of all identified bCA isoforms have been reported in the scientific literature for only three species: Arabidopsis thaliana (Schmid et al, 2005; Fabre et al, 2007; Winter et al, 2007; Ferreira et al, 2008; Wang et al, 2014; DiMario et al, 2016), F. bidentis (Tetu et al, 2007), and F. pringlei (Tanz et al, 2009). When the transformants did survive, the mature plants showed no phenotypic differences from WT plants, strongly suggesting that AtbCA1 plays no direct role in photosynthesis of mature Arabidopsis plants (Ferreira et al, 2008)
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