PLANT PHYSIOLOGY , Vol 109, Issue 4 1327-1335, Copyright © 1995 by American Society of Plant Biologists
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GENE REGULATION AND MOLECULAR GENETICS |
Molecular Characterization of the Plastidic Glucose-6-Phosphate Dehydrogenase from Potato in Comparison to its Cytosolic Counterpart
A. von Schaewen, G. Langenkamper, K. Graeve, I. Wenderoth and R. Scheibe
Pflanzenphysiologie, FB 5 Biologie/Chemie, Universitat Osnabruck, D-49069 Osnabruck, Germany
We report on the cloning of a plastidic glucose-6-phosphate dehydrogenase
(EC 1.1.1.49) from higher plants. The complete sequence of the plastidic
enzyme was obtained after rapid amplification of cDNA ends and comprises a
putative plastidic transit peptide. Sequences amplified from leaf or root
poly(A+) RNA are identical. In contrast to the cytosolic enzyme, the
plastidic isoform is subject to redox modulation, i.e. thioredoxin-mediated
inactivation by light. But when the plastidic enzyme is compared to a
cyanobacterial homolog, none of the cysteine residues is conserved. The
recombinant enzyme was used to raise antibodies in rabbits. Gene expression
was studied in potato (Solanum tuberosum L.), at both the RNA and protein
levels, revealing different patterns for the isoforms. The gene encoding
the cytosolic enzyme was transcribed in all tissues tested, and the highest
transcription was detected in tubers. In contrast, expression of the gene
encoding the plastidic enzyme was confined to green tissues. Wounding of
leaves resulted in a slight increase in the expression of the gene encoding
the cytosolic isoform and a shutdown of the plastidic counterpart. Compared
to the situation in soil, elevated transcription of the gene encoding the
plastidic enzyme is found in roots of hydroponically grown potato plants,
which is in agreement with the postulated role for this isoform in nitrite
reduction.
