PLANT PHYSIOLOGY , Vol 110, Issue 1 43-49, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Molecular Analysis of a New Member of the Opium Poppy Tyrosine/3,4-Dihydroxyphenylalanine Decarboxylase Gene Family
I. E. Maldonado-Mendoza, M. Lopez-Meyer, J. R. Galef, R. J. Burnett and C. L. Nessler
Department of Biology, Texas A&M University, College Station, Texas 77843-3258
An aromatic amino acid decarboxylase DNA fragment was generated from opium
poppy (Papaver somniferum L.) genomic DNA by the PCR using primers designed
from conserved amino acid sequences of other aromatic amino acid
decarboxylase genes. Using this fragment as a probe, a genomic clone was
isolated that encodes a new member of the opium poppy
tyrosine/3,4-dihydroxyphenylalanine decarboxylase gene family (TyDC5). The
predicted TyDC5 amino acid sequence shares extensive identity with other
opium poppy tyrosine/3,4-dihydroxyphenylalanine decarboxylases (84%), and
when expressed in Escherichia coli, it is active against tyrosine and to a
lesser extent against 3,4-dihydroxyphenylalanine. Ribonuclease protection
assays indicate that TyDC5 is expressed primarily in the roots of mature
poppy plants. A peak of TyDC5 expression was also observed during
germination, coincident with the emergence of the radicle from the seed
coat. Parallel results were obtained in transgenic tobacco using a TyDC5
promoter fragment (-2060) translationally fused to the [beta]-glucuronidase
reporter gene (GUS). In TyDC5::GUS tobacco, GUS activity transiently
appeared in all parts of the seedling during germination, but was limited
to the roots in older plants. These results indicate that TyDC5 expression
is transcriptionally regulated and suggest that the TyDC5 enzyme may play
an important role in providing precursors for alkaloid synthesis in the
roots and germinating seedlings of opium poppy.
