Genetic analysis of the regulation of TCH gene expression, Final Report Page: 2 of 5
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Chehab, E.W., Eich, E., Braam, J. Thigmomorphogenesis: A compex plant response to
mechano-stimulation, Accepted, pending revision.
Summary:
The Arabidopsis TCH genes have complex regulation of expression. The TCH genes are
very rapidly upregulated in expression with an increase in transcript level detectable by
northern blots within five minutes. The expression is strong and transient, with a return
to basal levels within one to two hours. The TCH genes, originally isolated as a
consequence of their upregulation in response to the mechanical stimulus of touch, are
also upregulated by a variety of seemingly disparate environmental and hormonal stimuli.
To gain insight into the complexities of TCH gene regulation, we took a number of
approaches.
We sought to identify whether there was a common cis element that conferred the
diverse aspects of TCH4 regulation of expression or whether distinct elements could be
identified. We found that induction of expression by the diverse stimuli of touch,
darkness, cold, heat and brassinosteroids is conferred to reporter genes by the same 102
bp 5' untranscribed TCH4 region. This result is consistent with the idea that shared
regulatory elements are employed by diverse stimuli. Distal regions influence magnitude
of kinetics of expression and likely harbor regulatory elements that are redundant with
those located more proximal to the transcriptional start site. Substitution of the proximal
regulatory region sequences in the context of distal elements does not disrupt inducible
expression. TCH4 expression induction is transcriptional, at least in part because 5'-
untranscribed sequences are sufficient to confer this regulation. However, 5' untranslated
sequences are necessary and sufficient to confer the marked transience of TCH4
expression, most likely through an effect on mRNA stability. Perception of BR is not
necessary for TCH4 induction by environmental stimuli because regulation is intact in the
BR-insensitive mutant, bril-2. The full response to auxin, however, requires the
functioning of BRI]. Developmental expression of TCH4 is unlikely to mediated by BR
because TCH4:: GUS is expressed in BR perception and biosynthetic mutants bril-2 and
det2-1, respectively.
Because the 102 bp region shown to be sufficient for most aspects of TCH4
regulation is related to sequences identified as responsible for regulation of the cold- and
touch-inducible CBF genes (Iliev et al., 2002; Zarka et al., 2003), we examined whether
TCH gene expression is appropriately regulated in the ice] mutant (supplied in
collaboration with Zhu). ICEl is the putative regulatory factor responsible for cold
induction of CBF expression (Chinnusamy et al., 2003). Results indicated that
inducibility of expression is intact in the ice] mutant although there may be differences in
the transience of the induced TCH expression.
In collaboration with Hirt, we examined the potential role of Map kinases in the
signal transduction pathways that function in TCH expression regulation. MKK2
overexpressor and mkk2 null plants were examined for TCH gene expression in
stimulated and control plants. These lines, described in Teige et al. (2004), were obtained
by driving a constitutively active MKK2-EE with the 35S CaMV promoter or by a T-
DNA insertion generating an mRNA null knock out mutant. Results indicated that MKK2
is not required for inducible TCH2, TCH3 or TCH4 expression.
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Braam, Janet. Genetic analysis of the regulation of TCH gene expression, Final Report, report, October 28, 2008; United States. (https://digital.library.unt.edu/ark:/67531/metadc896555/m1/2/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.