The Cytoplasmic Carbonic Anhydrases ßCA2 and ßCA4 Are Required for Optimal Plant Growth at Low CO2.

Plant physiology

PubMedID: 26993617

DiMario RJ, Quebedeaux JC, Longstreth D, Dassanayake M, Hartman MM, Moroney JV. The Cytoplasmic Carbonic Anhydrases ßCA2 and ßCA4 Are Required for Optimal Plant Growth at Low CO2. Plant Physiol. 2016;.
Carbonic anhydrases (CAs) are zinc metalloenzymes that interconvert CO2 and HCO3 (-) In plants, both a- and ß-type CAs are present. We hypothesize that cytoplasmic ßCAs are required to modulate inorganic carbon forms needed in leaf cells for carbon-requiring reactions such as photosynthesis and amino acid biosynthesis. In this report, we present evidence that ßCA2 and ßCA4 are the two most abundant cytoplasmic CAs in Arabidopsis (Arabidopsis thaliana) leaves. Previously, ßCA4 was reported to be localized to the plasma membrane, but here, we show that two forms of ßCA4 are expressed in a tissue-specific manner and that the two proteins encoded by ßCA4 localize to two different regions of the cell. Comparing transfer DNA knockout lines with wild-type plants, there was no reduction in the growth rates of the single mutants, ßca2 and ßca4 However, the growth rate of the double mutant, ßca2ßca4, was reduced significantly when grown at 200 µL L(-1) CO2 The reduction in growth of the double mutant was not linked to a reduction in photosynthetic rate. The amino acid content of leaves from the double mutant showed marked reduction in aspartate when compared with the wild type and the single mutants. This suggests the cytoplasmic CAs play an important but not previously appreciated role in amino acid biosynthesis.