PLANT PHYSIOLOGY , Vol 113, Issue 3 695-706, Copyright © 1997 by American Society of Plant Biologists
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GENE REGULATION AND MOLECULAR GENETICS |
Expression of an Aspartate Kinase Homoserine Dehydrogenase Gene Is Subject to Specific Spatial and Temporal Regulation in Vegetative Tissues, Flowers, and Developing Seeds
J. X. Zhu-Shimoni, S. Lev-Yadun, B. Matthews and G. Galili
Department of Plant Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel (J.X.Z.-S., S.L.-Y., G.G.)
Although the regulation of amino acid synthesis has been studied
extensively at the biochemical level, it is still not known how genes
encoding amino acid biosynthesis enzymes are regulated during plant
development. In the present report, we have used the [beta]-glucuronidase
(GUS) reporter gene to study the regulation of expression of an Arabidopsis
thaliana aspartate kinase-homoserine dehydrogenase (AK/HSD) gene in
transgenic tobacco plants. The polypeptide encoded by the AK/HSD gene
comprises two linked key enzymes in the biosynthesis of aspartate-family
amino acids. AK/HSD-GUS gene expression was highly stimulated in apical and
lateral meristems, lateral buds, young leaves, trichomes, vascular and
cortical tissues of growing stems, tapetum and other tissues of anthers,
pollen grains, various parts of the developing gynoecium, developing seeds,
and, in some transgenic plants, also in stem and leaf epidermal trichomes.
AK/HSD-GUS gene expression gradually dimished upon maturation of leaves,
stems, floral tissues, and embryos. GUS expression was relatively low in
roots. During seed development, expression of the AK/HSD gene in the embryo
was coordinated with the initiation and onset of storage protein synthesis,
whereas in the endosperm it was coordinated with the onset of seed
desiccation. Upon germination, AK/HSD-GUS gene expression in the hypocotyl
and the cotyledons was significantly affected by light. The expression
pattern of the A. thaliana AK/HSD-GUS reporter gene positively correlated
with the levels of aspartate-family amino acids and was also very similar
to the expression pattern of the endogenous tobacco AK/HSD mRNA as
determined by in situ hybridization.
