PLANT PHYSIOLOGY , Vol 113, Issue 1 45-57, Copyright © 1997 by American Society of Plant Biologists
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GENE REGULATION AND MOLECULAR GENETICS |
Cell-Specific Expression of the Promoters of Two Nonlegume Hemoglobin Genes in a Transgenic Legume, Lotus corniculatus
C. R. Andersson, D. J. Llewellyn, W. J. Peacock and E. S. Dennis
Division of Plant Industry, Commonwealth Scientific and Industrial Research Organization, G.P.O. Box 1600, Canberra, ACT 2601, Australia (C.R.A., D.J.L., W.J.P., E.S.D.)
The promoters of the hemoglobin genes from the nitrogen-fixing tree
Parasponia andersonii and the related nonnitrogen-fixing Trema tomentosa
both confer [beta]-glucuronidase reporter gene expression to the central
zone of the nodules of a transgenic legume, Lotus corniculatus.
[beta]-Glucuronidase expression was high in the uninfected interstitial
cells and parenchyma of the surrounding boundary layer and was low in the
Rhizobium-infected cells. This contrasts with the expression of both the P.
andersonii hemoglobin protein in P. andersonii nodules and the endogenous
Lotus leghemoglobins that are expressed in the infected cells at very high
levels. The expression pattern of the P. andersonii and T. tomentosa
hemoglobin promoters in L. corniculatus resembles that of a nonsymbiotic
hemoglobin gene from Casuarina glauca, which was introduced into this
legume, and suggests that only the nonsymbiotic functions of the P.
andersonii promoter are being recognized. Deletion of the distal segments
of both the P. andersonii and T. tomentosa promoters identified regions
important for the control of their tissue-specific and temporal activity in
Lotus. Potential regulatory elements, which enhance nodule expression and
suppress nonnodule expression, were also identified and localized to a
distal promoter segment. A proximal AAGAG motif is present in the P.
andersonii, T. tomentosa, and nonsymbiotic Casuarina hemoglobin genes.
Mutation of this motif in the P. andersonii promoter resulted in a
significant reduction in both the nodule and root expression levels in L.
corniculatus. Some of the regulatory motifs characterized are similar to,
but different from, the nodulin motifs of the leghemoglobins.
