First published online January 21, 2005; 10.1104/pp.104.056077
Plant Physiology 137:747-755 (2005)
© 2005 American Society of Plant Biologists
BIOENERGETICS AND PHOTOSYNTHESIS
Reductions of Rubisco Activase by Antisense RNA in the C4 Plant Flaveria bidentis Reduces Rubisco Carbamylation and Leaf Photosynthesis
Susanne von Caemmerer*,
L. Hendrickson,
V. Quinn,
N. Vella,
A.G. Millgate and
R.T. Furbank
Molecular Plant Physiology Group, Research School of Biological Sciences, Australian National University, Canberra, Australian Capital Territory 2601, Australia (S.v.C., L.H., V.Q.); Department of Biological Sciences, Macquarie University, Sydney, New South Wales 2109, Australia (N.V.); and Commonwealth Scientific and Industrial Research Organisation, Division of Plant Industry, Canberra, Australian Capital Territory 2601, Australia (A.G.M., R.T.F.)
To function, the catalytic sites of Rubisco (EC 4.1.1.39) need to be activated by the reversible carbamylation of a lysine residue within the sites followed by rapid binding of magnesium. The activation of Rubisco in vivo requires the presence of the regulatory protein Rubisco activase. This enzyme is thought to aid the release of sugar phosphate inhibitors from Rubisco's catalytic sites, thereby influencing carbamylation. In C3 species, Rubisco operates in a low CO2 environment, which is suboptimal for both catalysis and carbamylation. In C4 plants, Rubisco is located in the bundle sheath cells and operates in a high CO2 atmosphere close to saturation. To explore the role of Rubisco activase in C4 photosynthesis, activase levels were reduced in Flaveria bidentis, a C4 dicot, by transformation with an antisense gene directed against the mRNA for Rubisco activase. Four primary transformants with very low activase levels were recovered. These plants and several of their segregating T1 progeny required high CO2 (>1 kPa) for growth. They had very low CO2 assimilation rates at high light and ambient CO2, and only 10% to 15% of Rubisco sites were carbamylated at both ambient and very high CO2. The amount of Rubisco was similar to that of wild-type plants. Experiments with the T1 progeny of these four primary transformants showed that CO2 assimilation rate and Rubisco carbamylation were severely reduced in plants with less than 30% of wild-type levels of activase. We conclude that activase activity is essential for the operation of the C4 photosynthetic pathway.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.056077.
* Corresponding author; e-mail susanne.caemmerer{at}anu.edu.au; fax 61–2–61255075.
Received November 4, 2004;
returned for revision December 12, 2004;
accepted December 13, 2004.
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