First published online September 6, 2002; 10.1104/pp.008045
Plant Physiol, October 2002, Vol. 130, pp. 876-886
Photosynthetic and Other Phosphoenolpyruvate
Carboxylase Isoforms in the Single-Cell, Facultative C4
System of Hydrilla verticillata1
Srinath K.
Rao,
Noël C.
Magnin,2
Julia B.
Reiskind, and
George
Bowes*
Department of Botany, 220 Bartram Hall, P.O. Box 118526, University
of Florida, Gainesville, Florida 32611-8526
The submersed monocot Hydrilla verticillata (L.f.)
Royle is a facultative C4 plant. It typically exhibits
C3 photosynthetic characteristics, but exposure to low
[CO2] induces a C4 system in which the
C4 and Calvin cycles co-exist in the same cell and the
initial fixation in the light is catalyzed by
phosphoenolpyruvate carboxylase (PEPC). Three
full-length cDNAs encoding PEPC were isolated from H.
verticillata, two from leaves and one from root. The sequences
were 95% to 99% identical and shared a 75% to 85% similarity with
other plant PEPCs. Transcript studies revealed that one isoform,
Hvpepc4, was exclusively expressed in leaves during
C4 induction. This and enzyme kinetic data were consistent with it being the C4 photosynthesis isoform. However, the
C4 signature serine of terrestrial plant C4
isoforms was absent in this and the other H.
verticillata sequences. Instead, alanine, typical of
C3 sequences, was present. Western analyses of
C3 and C4 leaf extracts after anion-exchange
chromatography showed similar dominant PEPC-specific bands at 110 kD.
In phylogenetic analyses, the sequences grouped with C3,
non-graminaceous C4, and Crassulacean acid metabolism PEPCs
but not with the graminaceous C4, and formed a clade with a
gymnosperm, which is consistent with H. verticillata
PEPC predating that of other C4 angiosperms.
1
This work was supported by the National Science
Foundation (grant no. IBN-9604518) and by the U.S. Department of
Agriculture National Research Initiatives Competitive Grants
Photosynthesis and Respiration Program (grant no.
93-37306-9386).
2
Present address: Université Victor Segalen
Bordeaux 2, Centre de Bio-Informatique, 146 Rue Léo Saignat,
33076, Bordeaux, France.
*
Corresponding author; e-mail gbowes{at}botany.ufl.edu; fax
352-392-3993.
© 2002 American Society of Plant Physiologists
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