PLANT PHYSIOLOGY , Vol 109, Issue 1 293-297, Copyright © 1995 by American Society of Plant Biologists
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GENE REGULATION AND MOLECULAR GENETICS |
The diageotropica Mutation and Synthetic Auxins Differentially Affect the Expression of Auxin-Regulated Genes in Tomato
N. Mito and A. B. Bennett
Mann Laboratory, Department of Vegetable Crops, University of California, Davis, California 95616
The effect of a tomato (Lycopersicon esculentum) mutation, diageotropica
(dgt), on the accumulation of mRNA corresponding to tomato homologs of
three auxin-regulated genes, LeAux, LeSAUR, and Lepar, was examined. The
dgt mutation inhibited the induction of LeAux and LeSAUR mRNA accumulation
by naphthalene acetic acid (NAA) but had no effect on NAA-induced Lepar
mRNA accumulation. The effect of two synthetic auxins, NAA and
3,7-dichloro-8-quinoline caboxylic acid (quinclorac), on the accumulation
of LeAux, LeSAUR, and Lepar mRNA was also examined. Quinclorac induced the
expression of each of the auxin-regulated genes, confirming its proposed
mode of herbicidal action as an auxin-type herbicide. Concentrations of
quinclorac at least 100-fold higher than NAA were required to induce LeAux
and LeSAUR mRNA accumulation to similar levels, whereas Lepar mRNA
accumulation was induced by similar concentrations of NAA and quinclorac.
Collectively, these data suggest the presence of two auxin-dependent signal
transduction pathways: one that regulates LeSAUR and LeAux mRNA
accumulation and is interrupted by the dgt mutation and a second that
regulates Lepar mRNA accumulation and is not defective in dgt tomato
hypocotyls. These two auxin-regulated signal transduction pathways can be
further discriminated by the action of two synthetic auxins, NAA and
quinclorac.
