The Systems and Synthetic Biology of Auxin

AuxSynBio: synthetic biology tools to understand and engineer auxin

The plant hormone auxin is a crucial coordinator of nearly all plant growth and development processes. Because of its centrality to plant physiology and the modular nature of the signaling pathway, auxin has played a critical role at the forefront of plant synthetic biology. This review will highlight how auxin is both a subject and an object of synthetic biology. Engineering biology approaches are deepening our understanding of how auxin pathways are wired and tuned, particularly through the creative use of signaling pathway recapitulation in yeast and engineered orthogonal auxin-receptor pairs. Auxin biology has also been mined for parts by synthetic biologists, with components being used for inducible protein degradation systems (auxin-inducible degron), auxin biosensors, synthetic cell-cell communication, and plant engineering.

Fourteen Stations of Auxin

Auxin has always been at the forefront of research in plant physiology and development. Since the earliest contemplations by Julius von Sachs and Charles Darwin, more than a century-long struggle has been waged to understand its function. This largely reflects the failures, successes, and inevitable progress in the entire field of plant signaling and development. Here I present 14 stations on our long and sometimes mystical journey to understand auxin. These highlights were selected to give a flavor of the field and to show the scope and limits of our current knowledge. A special focus is put on features that make auxin unique among phytohormones, such as its dynamic, directional transport network, which integrates external and internal signals, including self-organizing feedback. Accented are persistent mysteries and controversies. The unexpected discoveries related to rapid auxin responses and growth regulation recently disturbed our contentment regarding understanding of the auxin signaling mechanism. These new revelations, along with advances in technology, usher us into a new, exciting era in auxin research.