Arabidopsis plastid carbonic anhydrase βCA5 is important for normal plant growth

Abstract

Carbonic anhydrases (CAs) are zinc-metalloenzymes that catalyze the interconversion of CO2 and HCO3-. In heterotrophic organisms, CAs provide HCO3- for metabolic pathways requiring a carboxylation step. Arabidopsis (Arabidopsis thaliana) has 14 α- and β-type CAs, two of which are plastid CAs designated as βCA1 and βCA5. To study their physiological properties, we obtained knock-out (KO) lines for βCA1 (SALK_106570) and βCA5 (SALK_121932). These mutant lines were confirmed by genomic PCR, RT-PCR, and immunoblotting. While βca1 KO plants grew normally, growth of βca5 KO plants was stunted under ambient CO2 conditions of 400 µL L−1; high CO2 conditions (30,000 µL L−1) partially rescued their growth. These results were surprising, as βCA1 is more abundant than βCA5 in leaves. However, tissue expression patterns of these genes indicated that βCA1 is expressed only in shoot tissue, while βCA5 is expressed throughout the plant. We hypothesize that βCA5 compensates for loss of βCA1 but, owing to its expression being limited to leaves, βCA1 cannot compensate for loss of βCA5. We also demonstrate that βCA5 supplies HCO3- required for anaplerotic pathways that take place in plastids, such as fatty acid biosynthesis.

Arabidopsis stromal carbonic anhydrases exhibit non‐overlapping roles in photosynthetic efficiency and development

“…Both MGDGs and DGDGs are involved in many aspects of photosynthesis and chloroplast integrity [(for review, see Li and Yu, 2018)]. Like βCA1, βCA5 supplies HCO 3 − , which is required for anaplerotic pathways in plastids, such as fatty acid biosynthesis (Weerasooriya et al., 2022). Moreover, similar to βca5 , an MGDG‐deficient mgd1 mutant displays reduced chlorophyll content and qN (NPQ), and no change in maximal PSII efficiency (Fv/Fm) compared with WT.…”

“…An earlier study on the tissue expression of βCAs showed that βCA 1, βCA 2 and βCA 4 are mainly expressed in the aboveground tissues with almost no expression in roots, whereas βCA3 , βCA5 and βCA6 are expressed in all parts of the plant but at a lower level in roots (Fabre et al., 2007; Weerasooriya et al., 2022). Furthermore, it was found that βCA5 is expressed at much lower levels than βCA1 , and that the expression of βCA5 and βCA1 is sensitive to CO 2 concentrations (Wang et al., 2014).…”

A carboxysome‐based CO2 concentrating mechanism for C3 crop chloroplasts: advances and the road ahead

“…To date, two separate plant lines have been generated wherein native CAs have been eliminated. Hines et al (2021) utilised CRISPR-Cas9 to knock out two tobacco stromal CAs (β-CA1 and β-CA5), while Weerasooriya et al (2022) used T-DNA insertion lines with inactivated plastid β-CA1 and β-CA5 in Arabidopsis thaliana. The stunted growth and reduced pollen fertility phenotypes of these plants, in particular of β-ca1/β-ca5, demonstrated that plastid CAs play an essential metabolic role in supplying bicarbonate for anaplerotic reactions (Hines et al, 2021;Weerasooriya et al, 2022).…”

OsαCA1 Affects Photosynthesis, Yield Potential, and Water Use Efficiency in Rice

“…In Arabidopsis, γ-type CAs are usually located in mitochondria as important subunits of mitochondrial complex I and are required for normal embryogenesis and photomorphogenesis [ 31 , 32 , 33 ]. β-type CAs have been demonstrated to be important to maintaining stomatal development and function as well as plant growth and responses to various stresses [ 34 , 35 , 36 , 37 , 38 ]. Although it has been suggested that AtαCA2, AtαCA4, and AtαCA5 are involved in photosynthetic light reactions, their corresponding functions and underlying mechanisms remain to be deciphered [ 39 , 40 , 41 ].…”