植物生长素受体的身份-Arabidopsis

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Nature 435: 7041
26 May 2005

1880年，Charles 和Frances Darwin出版了The Power of Movement in Plants，
书中描述了一个移动信号是怎样控制植物枝条朝向光线弯曲的。这种移动信号在上
个世纪20年代作为植物生长素被发现，它是植物生长大多数方面的关键调节物质。
植物生长素早就是生物学教科书中的一个固定内容，所以当您知道植物生长素受体
的身份此前一直不为人们所知时也许会感到吃惊。现在，两个独立的研究小组发
现，拟南芥的F-box蛋白TIR1是一个植物生长素受体。F-box蛋白在真核生物中的作
用是，对调节蛋白进行降解，这种作用依靠信号进行。（Articles, pp. 441,
446; News and Views）

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The Arabidopsis F-box protein TIR1 is an
auxin receptor
Stefan Kepinski1,2 & Ottoline Leyser1
Despite 100 years of evidence showing a pivotal role for indole-3-acetic acid (IAA or auxin) in plant development, the
mechanism of auxin perception has remained elusive. Central to auxin response are changes in gene expression, brought
about by auxin-induced interaction between the Aux/IAA transcriptional repressor proteins and the ubiquitin–ligase
complex SCFTIR1, thus targeting for them proteolysis. Regulated SCF-mediated protein degradation is a widely occurring
signal transduction mechanism. Target specificity is conferred by the F-box protein subunit of the SCF (TIR1 in the case
of Aux/IAAs) and there are multiple F-box protein genes in all eukaryotic genomes examined so far. Although
SCF–target interaction is usually regulated by signal-induced modification of the target, we have previously shown that
auxin signalling involves the modification of SCFTIR1. Here we show that this modification involves the direct binding of
auxin to TIR1 and thus that TIR1 is an auxin receptor mediating transcriptional responses to auxin

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The F-box protein TIR1 is an auxin receptor

Nihal Dharmasiri1, Sunethra Dharmasiri1 & Mark Estelle1
The plant hormone auxin regulates diverse aspects of plant growth and development. Recent studies indicate that auxin
acts by promoting the degradation of the Aux/IAA transcriptional repressors through the action of the ubiquitin protein
ligase SCFTIR1. The nature of the signalling cascade that leads to this effect is not known. However, recent studies
indicate that the auxin receptor and other signalling components involved in this response are soluble factors. Using an
in vitro pull-down assay, we demonstrate that the interaction between transport inhibitor response 1 (TIR1) and Aux/IAA
proteins does not require stable modification of either protein. Instead auxin promotes the Aux/IAA–SCFTIR1 interaction
by binding directly to SCFTIR1. We further show that the loss of TIR1 and three related F-box proteins eliminates
saturable auxin binding in plant extracts. Finally, TIR1 synthesized in insect cells binds Aux/IAA proteins in an auxindependent
manner. Together, these results indicate that TIR1 is an auxin receptor that mediates Aux/IAA degradation
and auxin-regulated transcription.