SPECIES-DEPENDENT VARIATION IN THE INTERACTION OF SUBSTRATE-BOUND RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE OXYGENASE (RUBISCO) AND RUBISCO ACTIVASE

Purified spinach (Spinacea oleracea L.) and barley (Hordeum vulgare L.) ribulose-1,5-bisphosphatecarboxylase/oxygenase(Rubisco) activase supported 50 to 100% activation of substrate-bound Rubisco from spinach, barley, wheat (Triticum aestivum L.), soybean (Glycine max L.), pea (Pisum sativum L.), Arabidopsis thaliana, maize (Zea mays L.), and Chlamydomonas reinhardtii but supported only 10 to 35% activation of Rubisco from three Solanaceae species, tobacco (Nicotiana tabacum L.), petunia (Petunia hybrida L.), and tomato (Lycopersicon esculentum L.). Conversely, purified tobacco and petunia Rubisco activase catalyzed 75 to 100% activation of substrate-bound Rubisco from the three Solanaceae species but only 10 to 25% activation of substrate-bound Rubisco from the other species. Thus, the interaction between substrate-bound Rubisco and Rubisco activase is species dependent. The species dependence observed is consistent with phylogenetic relationships previously derived from plant morphological characteristics and from nucleotide and amino acid sequence comparisons of the two Rubisco subunits. Species dependence in the Rubisco-Rubisco activase interaction and the absence of major anomalies in the deduced amino acid sequence of tobacco Rubisco activase compared to sequences in non-Solanaceae species suggest that Rubisco and Rubisco activase may have coevolved such that amino acid changes that have arisen by evolutionary divergence in one of these enzymes through spontaneous mutation or selection pressure have led to compensatory changes in the other enzyme.