Dr. Stefan Kepinski

email: s.kepinski@leeds.ac.uk

Auxin-regulated development and plant geometry

The Kepinski lab is focused on understanding the regulation of plant development by the hormone auxin with projects ranging from the earliest events of auxin receptor complex formation to root hair development and the control of growth angle of plant organs. We are always interested to hear from bright and committed researchers who would like to join the lab.

Current research

Auxin perception

The formation of the TIR1/AFB-auxin-Aux/IAA auxin receptor complex is one of the most pivotal protein/ligand interaction events in plant biology. In promoting the association between TIR1/AFB receptor F-box proteins and Aux/IAA co-repressors, endogenous auxins regulate almost every aspect of plant development from the earliest events of embryogenesis to the formation of flowers and fruits. The function of this complex is to control gene expression by regulating levels of Aux/IAA transcriptional co-repressor proteins in response to auxin; the auxin-enhanced interaction between TIR1/AFB proteins and Aux/IAAs promotes the polyubiquitnation of the Aux/IAAs, marking them for destruction in the 26S proteasome. Given the central importance of auxin for plant growth it is no surprise that the TIR1/AFB-auxin-Aux/IAA receptor complex is the target for auxinic agrochemicals, particularly herbicides, which include 2,4-D and picloram. Our current research on this topic revolves around understanding the very earliest events of auxin perception using structural, biophysical, and thermodynamic analysis.

Context-specificity in auxin signalling

A key question in plant biology is how the hormone auxin controls such a diversity of developmental events. Research in the Kepinski lab is focused on understanding how the specificity which can account for this control arises in the auxin signalling system. Although the current qualitative model of this complex system provides a conceptual framework for understanding how auxin can turn genes on and off, it is unclear how and where specific information is carried in the system and thus how auxin pulses of differing length and amplitude can be translated into quantitatively different genomic outputs both within and between various developmental contexts. To address these questions, we are obtaining quantitative and cell-type-specific genomic and biochemical data to parameterize comparative mathematical models of auxin response in juxtaposed developmental contexts to understand how auxin operates throughout development. Our principal model system is the root epidermis which is made up of hair cells that can produce root hairs and non-hair cells that typically do not. This tissue is of particular interest because these adjacent cell types have dramatically different capacities to transport and respond to auxin. Because of the desire to model, as far as possible, at the level of the single cell and with realistic binding preferences among protein components, we are heavily involved in single-cell-type sampling techniques and in vitro and in vivo quantification of protein interactions and abundance. We work closely with modellers at CPIB in Nottingham and to integrate the experimental and theoretical aspects of the work.

Growth angle control in lateral branches and organs

The growth angle of branches and other lateral organs is a fascinating topic in developmental biology and one of tremendous agronomic importance. For the most part root and shoot branches grow at angles that are non-vertical, a crucial adaptation allowing plants to optimise the capture of resources above- and below-ground. Importantly, many lateral branches are maintained at specific angles with respect to gravity rather than to the main or parent axis per se. These growth angles, known as gravitropic setpoint angles or GSAs, are intriguing because their maintenance requires that lateral root and shoot branches are able to effect tropic growth both with and against the gravity vector. We are using using genetics, molecular genetics, cell biology, and computational modelling to understand the mechanisms underlying gravity-dependent and gravity-independent growth angle control.

Current projects
  • Gravitropic setpoint angle control in higher plants (BBSRC, 2016-2019)

  • Next generation auxins and anti-auxins: principles for binding and design (BBSRC, 2014-2017) Collaboration with Prof. Richard Napier, Warwick

  • The molecular basis of antigravitropism (BBSRC DTP, 2015-2019)

  • Computational modelling of growth angle control across the higher plants (BBSRC DTP, 2013-2017) Collaboration with Prof. Netta Cohen, Leeds

  • Characterisation of novel regulators of auxin signalling (INRA, 2015-2017)

  • Protein Interactions in Auxin Signalling (BBSRC/Syngenta CASE, 2012-2016) Collaboration with Prof. Richard Napier, Warwick and Drs John Paul Evans and Tim Hawkes, Syngenta, Jealott’s Hill.

Surface plasmon resonance analysis of TIR1 binding to the Aux/IAAs AXR3/IAA17 and IAA28
Expression of the auxin co-receptor protein AFB3 in the Arabidopsis root
An Arabidopsis shoot system following horizontal clinorotation: Clinostats can be used to subject plants to omnilateral gravitational stimulation, removing their usually stable reference to the gravity and have been useful in probing the mechanisms of growth angle control in lateral branches