Environmental and hormonal regulation of gene expression of C₄ photosynthetic enzymes in the amphibious sedge Eleocharis vivipara

Eleocharis vivipara, an amphibious leafless sedge, develops C₄ traits with Kranz anatomy under terrestrial conditions and C₃ traits with non-Kranz anatomy under submerged conditions. To determine the molecular basis of these responses, we isolated a full-length cDNA for phosphoenolpyruvate carboxylase (PEPC) from culms, the photosynthetic organs of the terrestrial form, and investigated the expression of this gene and two previously isolated isogenes for pyruvate,Pi dikinase (PPDK). The gene for PEPC, designated pep1, was 3303 bp long with a single open reading frame of 2904 nucleodides. Phylogenetic analysis indicated that the PEP1 protein is located between a cluster of C₄-form PEPCs of C₄ grasses and another large cluster including C₃- and CAM-form PEPCs of dicots and monocots and C₄-form PEPCs of the C₄ Flaveria. The pep1 and the two PPDK isogenes, which encode chloroplastic and cytosolic PPDK, respectively, were expressed more strongly in culms of the terrestrial form than in those of the submerged form. The transcript levels were strictly modulated, even within a single plant growing both underwater and above the water surface. Exogenous application of abscisic acid (ABA) to the submerged form induced the enhanced expression of these genes in mature culms with non-Kranz anatomy, as well as in newly developing culms with Kranz anatomy, indicating the expression of C₄ genes without coordinate tissue differentiation.