PLANT PHYSIOLOGY , Vol 113, Issue 4 1427-1435, Copyright © 1997 by American Society of Plant Biologists
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GENE REGULATION AND MOLECULAR GENETICS |
Molecular Cloning of Mannose-6-Phosphate Reductase and Its Developmental Expression in Celery
J. D. Everard, C. Cantini, R. Grumet, J. Plummer and W. H. Loescher
Department of Horticulture, Michigan State University, East Lansing, Michigan 48824-1325 (J.D.E., R.G., W.H.L.)
Compared with other primary photosynthetic products (e.g. sucrose and
starch), little is known about sugar alcohol metabolism, its regulation,
and the manner in which it is integrated with other pathways.
Mannose-6-phosphate reductase (M6PR) is a key enzyme that is involved in
mannitol biosynthesis in celery (Apium graveolens L.). The M6PR gene was
cloned from a leaf cDNA library, and clonal authenticity was established by
assays of M6PR activity, western blots, and comparisons of the deduced
amino acid sequence with a celery M6PR tryptic digestion product.
Recombinant M6PR, purified from Escherichia coli, had specific activity,
molecular mass, and kinetic characteristics indistinguishable from those of
authentic celery M6PR. Sequence analyses showed M6PR to be a member of the
aldo-keto reductase superfamily, which includes both animal and plant
enzymes. The greatest sequence similarity was with aldose-6-phosphate
reductase (EC 1.1.1.200), a key enzyme in sorbitol synthesis in Rosaceae.
Developmental studies showed M6PR to be limited to green tissues and to be
under tight transcriptional regulation during leaf initiation, expansion,
and maturation. These data confirmed a close relationship between the
development of photosynthetic capacity, mannitol synthesis, and M6PR
activity.
