Hormone archaeology: Evolutionary biochemistry of the auxin signaling pathway


Signaling molecules, often referred to as hormones, are critical to coordinate growth and development in multicellular organisms. Often, the same hormone triggers different responses in different cells. This context-dependent output is mediated by functionally different copies of receptors and intracellular response proteins – such as transcription factors – that have arisen through gene duplications during evolution. While the complex hormone response pathways in “higher” organisms, involving many interdependent and interacting proteins are subject of intensive research efforts, a largely unexplored question is how such pathways emerged during evolution. We will here use the response to the plant hormone auxin to address this question. Auxin triggers numerous developmental and growth responses by regulating gene activity through a short pathway with three dedicated proteins, each represented by large families in “higher” flowering plants. These response proteins are a ubiquitin ligase receptor, a transcriptional inhibitor and a DNA-binding (ARF) transcription factor. Biochemical differences among these proteins, notably the ARF factors, determine locally different auxin response outputs. We have recently reconstructed the evolutionary history of the auxin response pathway and found that the system likely emerged by changes in the ubiquitin ligase/receptor and transcriptional inhibitor that allowed auxin-regulation of a pre-existing (proto-ARF) transcription factor. These proto-ARFs likely represent the ancestral function of the auxin pathway, are still present in freshwater green algae (Charophytes) and, based on sequence conservation, share many properties with land plant ARFs. In this project, we will use a combined protein biochemical and genetic approach to characterize the structure, regulation, target genes, mechanisms and biological function of the proto-ARFs in several Charophyte algal species, as well as in an early land plant – the liverwort Marchantia polymorpha. This evolutionary biochemical approach will allow to test the hypothesis that auxin subverted a pre-existing transcription factor. In addition, we will reveal the birth of the response system for this multifunctional hormone and help define its ancestral function prior to the evolution of complexity.





Prof. dr. D. Weijers

Verbonden aan

Wageningen University & Research, Agrotechnologie & Voedingswetenschappen, Biochemie (BIC)


01/07/2019 tot 30/06/2023