My lab is focussed on understanding how long distance signalling within the plant body allows their growth and development to be precisely regulated in both space and time. Plant shoot and root systems are shaped in response to range of environmental stimuli, including soil nutrient status and light availability. For instance, the degree of shoot branching in plants is strongly sensitive to both nitrate and phosphate levels in the soil – indicating long distance communication between the root and shoot system. A small number of hormonal signals, including auxin, cytokinin and strigolactone are implicated in the systemic coordination of plant development, both within root and shoot systems, and between them. We use a wide range of approaches, anchored by molecular genetics, to try and dissect these signalling mechanisms, and to understand how such a simple set of signals can allow such precise control of development at a whole plant level.
The hormone strigolactone (SL) coordinates multiple aspects of shoot development by triggering ubiquitin-mediated degradation of a small family of ‘SMAX1-LIKE’ (SMXL) proteins (Soundappan et al, 2015). SL acts through the DWARF14 (D14) receptor protein, and the E3 ubiquitin ligase complex SCFMAX2. Intriguingly, a second pathway also acts via SCFMAX2, and triggers degradation of SMAX1 itself in response to signalling through the KAI2 receptor, which is a close homologue of D14. Loss of MAX2 activity alters root system architecture, including increasing lateral root density, but it is currently unclear whether these effects are related to SL or KAI2 signalling, or to both. We are characterizing the relative contribution of these signalling pathways to root development, and aim to understand how specificity is achieved in downstream signalling events. SLs are secreted into the rhizosphere by many species of plant, and we are also investigating their possible role in plant-plant signalling.
The parallel nature of the SL and KAI2 signalling pathways points to an intriguing evolutionary history. It is currently thought that KAI2 signalling evolved in the algal ancestors of land plants, while D14-mediated SL signalling evolved much later. Paradoxically, SLs are synthesised and regulate development in early-diverging land plants that apparently lack the means for SL perception. We are interested in understanding how SLs are perceived in these early-diverging land plants, and how and when ‘modern’ SL receptors have evolved. Phylogenetic and structural analysis of the D14/KAI2 family suggests that, across land plants, a wide variety of small molecules may be perceived through this receptor family. We are interested in characterizing this diversity of receptors through structural and chemical biological approaches, and in exploring the potential to use these signalling circuits to modulate development in crop plants.
While we know a huge amount regarding how plants initiate flowering, we know almost nothing about the mechanisms that bring about the end of flowering. This project extends our previous work on the hormonal regulation of shoot architecture to look at the events which occur after flowering in both annual and perennial plants. How do plants know when to stop flowering, when to stop producing fruit and when to stop growing? We believe that three interacting 'post-floral processes' regulate the end of flowering, fruiting and growth. These processes -- floral arrest, carpic dominance and interchangeable dominance -- are very poorly characterised, and we aim to define their roles in post-floral development, and the molecular mechanisms by which they act. We hypothesise that differently wired interactions between these processes may result in the varied life-history strategies found between flowering species, and aim to test this idea.
This project builds on our long-standing interest in the regulation of shoot branching. Shoot branching, biomass and flowering are closely interlinked parameters that determine crop productivity and yield. Plants are inherently 'cautious' about resource use, and therefore limit their own growth, even when external factors (light, mineral nutrients, water) are not limiting. We want to identify the mechanisms that plants use to assess available resources, and the processing mechanisms that result in cautious growth. We aim to define the effects this has on plant growth, and particularly to assess whether self-limitation is a relevant factor in limiting crop yields under field conditions.