Overexpression of cytoplasmic C4 Flaveria bidentis carbonic anhydrase in
C3 Arabidopsis thaliana increases photosynthetic potential and biomass
Abstract
One of the important ways to improve photosynthetic capacity in C3
crops, such as rice and wheat, is to transfer efficient C4 characters to
them. Here, cytosolic carbonic anhydrase (βCA3) of the C4 Flaveria
bidentis (Fb), having low Km for CO2, was overexpressed under the
control of 35S promoter in Arabidopsis thaliana, a C3 plant, to enhance
its photosynthetic efficiency. Overexpression of CA resulted in higher
[HCO3-] in the cytosol of the overexpressors, and increased
endogenous phosphoenolpyruvate carboxylase activity generating
oxaloacetate that feeds into the tricarboxylic acid cycle. This provided
more carbon skeleton for increased synthesis of amino acids and
proteins. Further, transgenic expression of FbβCA3 in Arabidopsis led to
pleiotropic expression of several genes/proteins involved in chlorophyll
biosynthesis and photosynthesis leading to higher chlorophyll content
and photosynthetic capacity in the transformants. Due to the presence of
higher CO2 in the chloroplast, pleiotropic effect overexpressors had
enhanced CO2 assimilation, starch content, and plant dry weight. In
addition, transgenic plants had lower stomatal conductance, reduced
transpiration rate and higher water use efficiency. These results, taken
together, show that expression of C4 CA in the cytosol of a C3 plant can
indeed improve its photosynthetic capacity with enhanced water use
efficiency.