The plant hormone auxin regulates many aspects of plant growth and
development. At the cellular level, auxin can stimulate cell division, cell elongation, and
cell differentiation. Little is known about the molecular mechanisms that mediate auxin
action at this level, although changes in gene expression have been implicated in each of
them. An important step in elucidating the signal transduction steps involved in these
responses is the identification of intermediates that respond to auxin treatment within a
physiologically relevant range, and can be functionally linked to specific response(s).
The Aux/IAA family of auxin-regulated genes, which has been identified in several
species, may constitute such a group of signalling intermediates.
This dissertation reports on the isolation and characterization of eleven tomato
genes, LeIAA1 - 11, which are homologous to these Aux/IAA genes. Expression
characteristics in response to exogenously-applied auxin were determined in segments of
etiolated hypocotyls. The LeIAA genes fell into three kinetic classes and displayed
differential responsiveness to the treatment. Comparison of auxin-induced expression in
wild-type and the auxin-insensitive diageotropica (dgt) mutant revealed that induction of
only a subset of genes was affected by the mutation while the other genes retained wild-type response levels in the mutant. This finding indicates that at least two signal
transduction chains lead to auxin-induced gene expression, and the dgt gene product acts
on only one of them.
The expression pattern of nine LeIAA genes was determined in a wide variety of
tissue samples in order to link individual LeIAA genes with specific physiological
responses. To that end, a qualitative multiplex RT-PCR method was developed that
allowed quick assessment of relative expression levels in a large number of small RNA
samples. It was found that LeIAA10 expression was highest in tissues undergoing rapid
growth, suggesting a role for this gene in the process of cell expansion. The expression
of LeIAA1 1 was also variable during development, while LeIAA2 was strongly down-regulated
after light treatment. These experiments demonstrated organ-preferential
expression of LeIAA genes under the control of environmental factors and depending on
developmental stages. The LeIAA genes may thus act as integrators of several other
signals with the auxin stimulus. / Graduation date: 1998
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33722 |
| Date | 05 September 1997 |
| Creators | Nebenfuhr, Andreas |
| Contributors | Lomax, Terri L. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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