Plant Carbonic Anhydrases: Structures, Locations, Evolution, and Physiological Roles

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.

An effective antioxidant defense provides protection against zinc deficiency‐induced oxidative stress in Zn‐efficient maize plants

“…Zn deficiency has also been shown to decrease CO 2 concentration that results from the decreased activity of a Zn-dependent enzyme, carbonic anhydrase (Sharma et al, 1995;Li et al, 2013;Sharma et al, 1994). Studies revealed that carbonic anhydrase is involved in a CO 2 -sensing pathway in guard cells (DiMario et al, 2017) and adaptation to drought stress (Wang et al, 2016).…”

What is the fate of xylem‐transported CO2 in Kranz‐type C4 plants?

“…If apoplastic CA are discovered in the future, it would suggest that significant apoplastic transport of CO 2 * is possible, otherwise, it is likely that most transport is via symplastic routes. In C 4 plants CA activities are more than four times higher in mesophyll cells than in bundle sheath cells (DiMario et al ., ). The 13 CO 2 * that diffuses past the bundle sheath cells to the mesophyll cells may be kept at equilibrium by CA, maintaining the supply of CO 2 for Rubisco.…”

SpHMA1 is a chloroplast cadmium exporter protecting photochemical reactions in the Cd hyperaccumulator Sedum plumbizincicola

“…However, the Zn concentration in the chloroplasts of SpHMA1 RNAi transgenic plants was not significantly different from those in wild‐type plants (Figure S8), suggesting that SpHMA1 is specific for Cd export in planta. Zn is an essential micronutrient that plays an important role as a catalytic and structural element in some chloroplast enzymes such as the Cu/Zn superoxide dismutase and carbonic anhydrase (DiMario, Clayton, Mukherjee, Ludwig, & Moroney, ; Gupta, Heinen, Holaday, Burke, & Allen, ). By contrast, Cd is non‐essential and highly toxic to plants at low concentrations.…”