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Quint, M., Drost, H-G., Gabel, A., Ullrich, K., Bönner, M. & Grosse, I. A transcriptomic hourglass in plant embryogenesis Nature 490, 98-101, (2012)

Animal and plant development starts with a constituting phase called embryogenesis, which evolved independently in both lineages1. Comparative anatomy of vertebrate developmentbased on the Meckel-Serrès law2 and von Baers laws of embryology3 from the early nineteenth centuryshows that embryos from various taxa appear different in early stages, converge to a similar form during mid-embryogenesis, and again diverge in later stages. This morphogenetic series is known as the embryonic hourglass4, 5, and its bottleneck of high conservation in mid-embryogenesis is referred to as the phylotypic stage6. Recent analyses in zebrafish and Drosophila embryos provided convincing molecular support for the hourglass model, because during the phylotypic stage the transcriptome was dominated by ancient genes7 and global gene expression profiles were reported to be most conserved8. Although extensively explored in animals, an embryonic hourglass has not been reported in plants, which represent the second major kingdom in the tree of life that evolved embryogenesis. Here we provide phylotranscriptomic evidence for a molecular embryonic hourglass in Arabidopsis thaliana, using two complementary approaches. This is particularly significant because the possible absence of an hourglass based on morphological features in plants suggests that morphological and molecular patterns might be uncoupled. Together with the reported developmental hourglass patterns in animals, these findings indicate convergent evolution of the molecular hourglass and a conserved logic of embryogenesis across kingdoms.


Tan, X., Calderón Villalobos, L.I., Sharon, M., Zheng, C., Robinson, C.V., Estelle, M. & Zheng, N. Mechanism of auxin perception by the TIR1 ubiquitin ligase Nature 446(7136), 640-645, (2007)


Auxin is a pivotal plant hormone that controls many aspects of plant growth and development. Perceived by a small family of F-box proteins including transport inhibitor response 1 (TIR1), auxin regulates gene expression by promoting SCF ubiquitin-ligase-catalysed degradation of the Aux/IAA transcription repressors, but how the TIR1 F-box protein senses and becomes activated by auxin remains unclear. Here we present the crystal structures of the

TIR1–ASK1 complex, free and in complexes with three different auxin compounds and an Aux/IAA substrate peptide. These structures show that the leucine-rich repeat domain of TIR1 contains an unexpected inositol hexakisphosphate co-factor and recognizes auxin and the Aux/IAA polypeptide substrate through a single surface pocket. Anchored to the base of the TIR1 pocket, auxin binds to a partially promiscuous site, which can also accommodate various auxin analogues. Docked on top of auxin, the Aux/IAA substrate peptide occupies the rest of the TIR1 pocket and completely encloses the hormone-binding site. By filling in a hydrophobic cavity at the protein interface, auxin enhances the TIR1–substrate interactions by acting as a ‘molecular glue’. Our results establish the first structural model of a plant hormone receptor.

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