Phosphoenolpyruvate carboxylase in the stem of the submersed species Egeria densa may be involved in an inducible C4-like mechanism

• Five plant-type PEPC isoforms and one partial bacterial-type PEPC isoform of Egeria densa were identified.
• The activity and amount of PEPC increased significantly in the leaves and stems after the low [CO2] cultivation.
• EdPEPC1 was up-expressed in the stems and leaves after the low [CO2] cultivation, and may be the C4-form.

The submersed species Egeria densa possesses an inducible C4-like photosynthetic system after exposure to low CO2 concentrations. Four full-length and one partial cDNAs encoding plant-type PEPC were identified, named EdPEPC1-5; and one partial cDNA encoding bacterial-type PEPC was identified. None of the C4-signature amino acid substitutions which were found in C4-type PEPC isoforms of terrestrial C4 plants were found in EdPEPCs. Real-time qPCR experiments indicated that in the high CO2 concentration, all these isoforms were expressed at low levels in leaves and stems. However after exposure to low CO2 concentration, EdPEPC1 was significantly up-expressed in the stems and leaves, and may thus correspond to the C4-form. The results of enzyme assays and western blotting showed increases in the activities and amount of PEPC in the leaves and stems after incubation at low [CO2]. EdPEPC1, gene that responds to low [CO2], might be involved in the emergence of the inducible C4-like mechanism in E. densa. For the first time in submersed plants, the results suggested that stems as well as leaves were likely to be involved in the C4-like mechanism.