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 C4Flaveria 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 C3plant can indeed improve its photosynthetic capacity with enhanced water
use efficiency.