The phosphoenolpyruvate carboxylase (ppc) gene family of Flaveria trinervia (C4) and F. pringlei (C3): molecular characterization and expression analysis of the ppcB and ppcC genes.

Phosphoenolpyruvate carboxylase (PEPC) is a central enzyme of C4 and CAM photosynthesis but plants, in addition, contain various non-photosynthetic isoforms with characteristic and variable functions. The partial sequence and a detailed expression analysis of the PpcB and PpcC genes which encode non-photosynthetic PEPC isoforms in the C4 plant Flaveria trinervia and the C3 species F. pringlei is presented. Southern analyses showed that PpcB and PpcC sequences are most probably of single-copy in the genomes of F. trinervia and F. pringlei. With gene-specific probes the various ppc transcripts could be distinguished unequivocally from one another and the expression patterns of all ppc genes were compared. PpcB and PpcC transcripts of both F. trinervia and F. pringlei were detected preferentially in roots and stems and at low levels in leaves. Their accumulation patterns are thus similar to each other, but different from that of the PpcA genes which in F. trinervia encode the C4 isoform of PEPC. Transgenic analysis of the 5'-flanking regions of the PpcB genes of both F. trinervia and F. pringlei in tobacco revealed that the PpcB promoter/beta-glucuronidase reporter genes were preferentially expressed in the phloem and the roots. Comparison of the PpcB promoter/reporter gene with the accumulation pattern of the PpcB transcripts in F. trinervia and F. pringlei suggests that the expression of the PpcB genes is predominantly controlled by transcription.