The C4 specific properties of Flaveria trinervia phosphoenolpyruvate carboxylase is divided in two regions that synergetically interact

Abstract

The evolution of the C4 photosynthetic pathway was facilitated by the reqruitment of genes already present in ancestral C3 plants. In order to function in the C4 cycle not only the level and pattern of expression of these genes had to be changed, but also the enzymatic properties had to be optimised. The C4 phosphoenolpyruvate carboxylase gene (ppcA) of the C4 species F. trinervia and its orthologous counterpart of the C3 plant F. pringlei were chosen to identify the C4-specific property determinants in the enzyme sequence. By constructing a series of C3/C4 chimerical enzymes it was shown that the serine residue at position 774 is crucial for the C4 enzyme. The results also suggested that region 2 (amino acids 296 to 437) contains additional determinant(s) for C4 properties in Flaveria phosphoenolpyruvate carboxylases. In the present work we investigated the influence of region 2 alone and in combination with site-directed C3/C4 mutagenesis of position 774. The results show that region 2 contains determinants for C4 properties. However, in order to transform a C3 enzyme into C4 type both region 2 and position 774 must be of C4 sequences. In addition, we will present results that show that a synergistic interaction exists between the two C4 specific determinants.