Calderon-Villalobos, L. I.; Tan, X.; Zheng, N.; Estelle, M. Auxin Perception—Structural Insights Cold Spring Harb Perspect Biol 2, a005546, (2010) DOI: 10.1101/cshperspect.a005546
The identity of the auxin receptor(s) and the mechanism of auxin perception has been a subject of intense interest since the discovery of auxin almost a century ago. The development of genetic approaches to the study of plant hormone signaling led to the discovery that auxin acts by promoting degradation of transcriptional repressors called Aux/IAA proteins. This process requires a ubiquitin protein ligase (E3) called SCFTIR1 and related SCF complexes. Surprisingly, auxin works by directly binding to TIR1, the F-box protein subunit of this SCF. Structural studies demonstrate that auxin acts like a molecular glue, to stabilize the interaction between TIR1 and the Aux/IAA substrate. These exciting results solve an old problem in plant biology and reveal new mechanisms for E3 regulation and hormone perception.
The history of plant biology is inexorably
intertwined with the conception and discovery of auxin, followed by the
many decades of research to comprehend its action during growth and
development. Growth responses to auxin are complex and require the
coordination of auxin production, transport, and perception. In this
overview of past auxin research, we limit our discourse to the mechanism
of auxin action. We attempt to trace the almost epic voyage from the
birth of the hormonal concept in plants to the recent crystallographic
studies that resolved the TIR1-auxin receptor complex, the first
structural model of a plant hormone receptor. The century-long endeavor
is a beautiful illustration of the power of scientific reasoning and
human intuition, but it also brings to light the fact that decisive
progress is made when new technologies emerge and disciplines unite.