Guanylate cyclase activity of TIR1/AFBs auxin receptors

Plants are the dominant multicellular organisms on Earth, accounting for the majority of its biomass. They are critical for the survival of most other organisms most notably animals, including humans while also having a major positive impact on the global climate. As plants evolved multicellularity independently of animals, they developed unique and fascinating solutions for many problems that complex organisms face - often very different to those evolved in animals. Thus, in many aspects, plants can be considered as extraterrestrials among us, offering biologists a model with which to study alternative mechanisms of how to deal with the challenges of life. This is also largely reflected in the survival strategies of plants: Whereas animals often react to adverse conditions by fighting or running away, plants are rooted, and thus must stay and adapt their physiology and development to survive. Thus, during their evolution, plants perfectly optimized their extraordinary developmental flexibility, which became their trump card in surviving ever-changing and often adverse environments. Such flexible development requires efficient and rapid coordination between different plant parts and in response to signals perceived from the environment. As plants to do not possess a nervous system in the classical sense, this type of signaling relies heavily on chemical signaling substances called plant hormones. Among plant hormones, auxin is the most prominent regulator determining plant shape, as well as many environmental growth responses, such as roots growing downwards (root gravitropism) and shoots upwards and towards light. The auxin cell mechanisms managing all these activities were believed to have been explained in 2005. The main result of this signaling mechanism happens in the nucleus, where hundreds-to-thousands of genes are switched on and produce proteins, which subsequently change the behavior of the cell. This slow mechanism, which typically takes about 10 minutes to have an effect, seems to explain many of auxins activities in regulating plant development. However, some very important auxin cellular effects are extremely fast, occurring within just a few seconds. These effects include alterations in electric charge, as well as calcium and proton transport at the plasma membrane - processes mediating the ability of roots to grow downwards. The mechanism behind these rapid auxin effects has remained a mystery for decades: unravelling this mystery is the primary aim of this project. To achieve this, we will employ a highly interdisciplinary strategy, combining molecular physiology (hormone signalling), developmental biology (gravity-regulated root growth), cell biology (advanced microscopy), biochemistry and molecular genetics methods. The ultimate goal is to understand how hormone signalling in plants can act very swiftly on cell activities and thus rapidly adjust plant growth and development in response to external signals.