PLANT PHYSIOLOGY , Vol 104, Issue 4 1411-1417, Copyright © 1994 by American Society of Plant Biologists
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MOLECULAR BIOLOGY AND GENE REGULATION |
Plant [delta]-Aminolevulinic Acid Dehydratase (Expression in Soybean Root Nodules and Evidence for a Bacterial Lineage of the Alad Gene)
C. M. Kaczor, M. W. Smith, I. Sangwan and M. R. O'Brian
Department of Biochemistry, State University of New York at Buffalo, Buffalo, New York 14214 (C.M.K., I.S., M.R.O'B.)
We isolated a soybean (Glycine max) cDNA encoding the heme and chlorophyll
synthesis enzyme [delta]-aminolevulinic acid (ALA) dehydratase by
functional complementation of an Escherichia coli hemB mutant, and we
designated the gene Alad. ALA dehydratase was strongly expressed in nodules
but not in uninfected roots, although Alad mRNA was only 2- to 3-fold
greater in the symbiotic tissue. Light was not essential for expression of
Alad in leaves of dark-grown etiolated plantlets as discerned by mRNA,
protein, and enzyme activity levels; hence, its expression in subterranean
nodules was not unique in that regard. The data show that soybean can
metabolize the ALA it synthesizes in nodules, which argues in favor of
tetrapyrrole formation by the plant host in that organ. Molecular
phylogenetic analysis of ALA dehydratases from 11 organisms indicated that
plant and bacterial enzymes have a common lineage not shared by animals and
yeast. We suggest that plant ALA dehydratase is descended from the
bacterial endosymbiont ancestor of chloroplasts and that the Alad gene was
transferred to the nucleus during plant evolution.
