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Plant Physiol, November 2001, Vol. 127, pp. 937-948
The Arabidopsis Protein SHI Represses Gibberellin Responses in
Arabidopsis and Barley1
Ingela
Fridborg,2
Sandra
Kuusk,
Masumi
Robertson, and
Eva
Sundberg*
Department of Physiological Botany, Evolutionary Biology Centre,
Uppsala University, Villavägen 6, S-752 36 Uppsala, Sweden
(I.F., S.K., E.S.); and Commonwealth Scientific and Industrial Research
Organization Plant Industry, G.P.O. Box 1600, Canberra, Australian
Capital Territory 2601, Australia (M.R.)
The current model of gibberellin (GA) signal transduction is
based on a derepressible system and a number of candidate negative regulators have been identified in Arabidopsis. We previously have
reported the identification of the Arabidopsis gene SHORT INTERNODES (SHI) that causes suppression of GA
responses when constitutively activated. In this paper, we show by
using reporter gene analysis that the SHI gene is
expressed in young organs, e.g. shoot apices and root tips. The model
predicts a suppressor of GA responses to be active in these tissues to
prevent premature growth or development. To study the effect of SHI on
GA signaling, we used a functional assay that measures effects of
signaling components on a well-defined GA response; the up-regulation
of  -amylase in barley (Hordeum vulgare) aleurones in
response to GA treatment. We found that SHI was able to specifically
block the activity of a high-isoelectric point -amylase promoter
following GA3 treatment, which further supports that SHI is
a suppressor of GA responses. We have identified two putative
loss-of-function insertion alleles of SHI and lines
homozygous for either of the new alleles show no phenotypic deviations
from wild type. Because SHI belongs to a gene family
consisting of nine members, we suggest that SHI and the
SHI-related genes are functionally redundant. We also
show that a functional ERECTA allele is able to partly suppress the dwarfing effect of the shi gain-of-function
mutation, suggesting that the erecta mutation harbored
by the Landsberg erecta ecotype is an enhancer of the
shi dwarf phenotype.
1
This work was supported by grants from the
Swedish Council for Forestry and Agricultural Research.
2
Present address: Department of Disease and Stress
Biology, John Innes Centre, Norwich Research Park, Colney, Norwich NR4
7UH, UK.
*
Corresponding author; e-mail Eva.Sundberg{at}ebc.uu.se; fax
46-18-559885.
© 2001 American Society of Plant Physiologists
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