|Van De Loo, Frank|
Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2002
Publication Date: 10/22/2002
Citation: SALVUCCI, M.E., VAN DE LOO, F.J., STECHER, D. TWO ISOFORMS OF RUBISCO ACTIVASE IN COTTON, THE PRODUCTS OF SEPARATE GENES NOT ALTERNATIVE SPLICING.. PLANTA. 2003. v 216: 736-744. Interpretive Summary: In the process of photosynthesis, plants convert light into chemical energy. The energy produced by photosynthesis is then used to power the conversion of carbon dioxide to sugars and other foodstuffs. The enzyme, Rubisco, is responsible for the first step in the conversion of carbon dioxide to sugar, and this enzyme is controlled by another enzyme called Rubisco activase. Since Rubisco activity limits photosynthesis, the regulation of Rubisco is a major factor controlling photosynthesis and plant productivity. In this study, we found that activase in cotton is composed of two forms. Two forms of activase have also been detected in other plant species, originating from a single activase gene. In contrast, our results show that activase in cotton is produced by two separate genes. These findings provide useful information about the possible functional roles of the two forms of activase in plants. This information might eventually be used to make changes in cotton activase that could enhance photosynthetic activity under some conditions. Improvements in activase would be especially useful for improving the efficiency of photosynthesis under heat stress.
Technical Abstract: In several plants, Rubisco activase consists of two isoforms that are produced by alternative splicing of a pre-mRNA. Two forms of activase corresponding to the longer, alpha and the shorter, beta forms were detected in cotton (Gossypium hirsutum L.) leaves, but their N-termini differed. The cDNAs for the forms of cotton activase diverged throughout the translated and 3'-untranslated regions, including variations that accounted for the differences in amino acid sequence. Analysis of genomic DNA confirmed that separate genes encoded the two forms of cotton activase. Separate activase genes were also detected in diploid species of cotton, indicating that the occurrence of separate activase genes predates merger of the diploid genomes. The deduced amino acid sequences of the two forms of cotton activase exhibited 84% identity and both were active after expression in Escherichia coli. The forms of activase exhibited similar affinities for ATP and only minor differences in thermotolerance, but their ATPase specific activities differed. The results show for the first time a plant species with two forms of activase that are equivalent to the alternatively spliced alpha and beta forms in other plants, but that are encoded by separate genes. That cotton still expresses both forms of activase, even without alternative splicing, suggests that each form has a required function in photosynthesis.