Structure and expression of a sugarcane gene encoding a housekeeping phosphoenolpyruvate carboxylase

Abstract

Two genes encoding phosphoenolpyruvate carboxylase (PEPC) have been isolated from the C-4 plant, sugarcane (Saccharum hybrid var. H328560), SCPEPCDI and SCPEPCD2. SCPEPCDI is ca. 6800bp long, with 10 exons. Positions of the 9 introns are identical to those in a maize C-4 PEPC gene (Hudspeth & Grula 1989) and M.crystallinum CAM and housekeeping PEPC genes (Cushman et al 1989). The entire gene sequence from -1561 to ca. 300bp downstream of the putative poly-A addition signal is reported. DNA binding sites conserved in the upstream region of maize and sorghum C-4 specific PEPC genes could not be recognized in this gene. Deduced amino acid sequence of this gene is more similar to plant housekeeping PEPCs than to C-4 specific forms. A motif proposed to act as a substrate site in light mediated activation of photosynthetic PEPC enzymes is present in the SCPEPCD1 protein; evidence is presented for the presence of this site in other housekeeping PEPC proteins. SCPEPCDI is expressed at low levels in all tissues, but is diminished in leaves during light induced greening. SCPEPCD2 is expressed relatively abundantly in greening leaves but at much lower levels in stems, a pattern consistent with C-4 specific PEPC genes.