PLANT PHYSIOLOGY , Vol 111, Issue 1 259-267, Copyright © 1996 by American Society of Plant Biologists
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GENE REGULATION AND MOLECULAR GENETICS |
Attenuation of the Phenotype Caused by the Root-Inducing, Left-Hand, Transferred DNA and Its rolA Gene (Correlations with Changes in Polyamine Metabolism and DNA Methylation)
J. Martin-Tanguy, L. Y. Sun, D. Burtin, R. Vernoy, N. Rossin and D. Tepfer
Station de Genetique et d'Amelioration des Plantes, Institut National de la Recherche Agronomique, BV 1540, 21034, Dijon Cedex, France (J.M.-T., D.B., R.V., N.R.)
We present four examples of attenuation of the transformed phenotype caused
by the root-inducing, left-hand, transferred DNA from Agrobacterium
rhizogenes in tobacco (Nicotiana tabacum). The first was associated with a
genetic variable (homozygosity for the T-DNA), and the second was induced
at the physiological level by putrescine and tyramine, suggesting that the
transformed phenotype depends on defective polyamine metabolism.
Physiological attenuation is further illustrated in the third example, in
which the inhibition of flowering caused by P35S-rolA, a gene from the
root-inducing, left-hand, transferred DNA driven by a strong viral
promoter, was attenuated by grafting the transformed shoot onto
non-transformed rootstock that had been induced to flower. Infertility in
the resulting flowers was corrected by a mixture of putrescine and
tyramine, indicating that P35S-rolA inhibited flowering through
interference with polyamine conjugation and that tyramine was essential to
fertility. A fourth example of attenuation of the transformed phenotype
occurred in lateral branches of plants expressing rolA under the control of
its native promoter. In these branches, reduction in the accumulation of
rolA transcripts was correlated with the methylation of a site 3[prime] to
the rolA coding sequence; thus, the transformed plant seems capable of
recognizing and repressing a gene that interferes with flowering.
