Pathways to neo-functionalization: the past and future of strigolactone signalling

Hormonal signalling pathways are vitally important in the regulation of plant growth and development. Strigolactones (SLs) and 'KAI2-Ligand' (KL) are closely related hormonal signals that regulate specific aspects of development, including shoot branching and seed germination. In flowering plants, including most crop plants, SL and KL act through very closely related signalling pathways to regulate development. In evolutionary terms, SL signalling appears to have arisen by duplication of the KL signalling pathway. Indeed, in non-flowering plants, there is evidence that the SL and KL signalling pathways overlap at least partially. This raises very intriguing questions as to whether the signalling pathways in flowering plants are truly separate, or whether they partially or even fully overlap.

This project aims to assess to what extent the SL and KL signalling pathways in flowering plants are separated from each other, and to understand at a molecular level how this 'specificity' arises. The main hypothesis we will test is that the perception of SL and KL by receptor proteins is highly specific, but that the mechanisms by which these pathways regulate development are very similar and at least partially overlapping. To address this question, the project will bring together a wealth newly available genomic data, with a powerful experimental system in the model plant Arabidopsis thaliana. By assessing how SL and KL signalling have evolved throughout the 500 million year history of land plants, we can formulate hypotheses regarding the specificity of these pathways, which we can then test in the context of Arabidopsis lateral root development. This project will allow us to understand how plants could be bred to enhance or diminish certain effects of SL or KL in order to improve yields. In summary, by analysing the past and present of SL and KL signalling, we can define possibilities for future crop improvement.

Hormonal signalling pathways are vitally important in the regulation of plant growth and development. In flowering plants, strigolactones (SLs) and 'KAI2-Ligand' (KL) are closely related hormonal signals that regulate specific aspects of development, including shoot branching (by SL) and seed germination (by KL). SL and KL signal through closely related receptor proteins to promote the degradation of closely related target proteins. In evolutionary terms, SL signalling appears to have arisen by neo-functionalization of duplicated KL signalling components. This re-specification may have occurred in at least four different ways, and as such the SL-KL system represents an excellent opportunity to understand how neo-functionalization can result in novel signalling pathways. Inversely, studying the neo-functionalization of SL signalling provides a novel way to understand the mechanistic basis for the upstream specificity and downstream effects of the SL signalling pathway. The overarching hypothesis the project aims to test is that while SL and KL have highly specific upstream signalling pathways, they regulate development through the same downstream effectors. To address this hypothesis, we will use an innovative synthesis of evolutionary-driven hypotheses with powerful molecular genetic and biochemical approaches. We will exploit natural diversity in the SL/KL receptor and target protein families to define how the specificity of their physical interactions is determined, and use the well-characterized system of Arabidopsis lateral root development to identify downstream effectors of SL and KL signalling, and to assess whether these overlap. Our ultimate goal is to assess the future possibility of re-engineering SL/KL signalling pathways in crop plants to maximize yields.

The proposed research program will uncover the mechanisms by which strigolactone signalling specifically regulates architectural traits in both the shoot and root system.

The anticipated beneficiaries, and they ways in which they will benefit from the research are:

Plant science research community:
As this is a fundamental science proposal, in the short-term (lifetime of the grant) the main impact will be advancement of knowledge for the plant science community. The project is aligned with the BBSRC strategic priority of sustainably enhancing agricultural production through more efficient and more sustainable use of resources - nutrients (fertiliser/feed/waste), water, energy - in crop or animal production. The academic community will benefit from the research through the new knowledge gained and through the new research questions generated.

Individuals on grant
This project will provide an excellent opportunity to deliver impact through training the next generation of academic or industrial scientists. The individuals on the project will become highly skilled researchers in an identified skills shortage area. The individuals will develop high level scientific skills alongside a range of transferrable skills, including project management, data analysis and communication/presentation skills. By the end of the grant, the individuals will be in a strong position to further develop their career in academia or industry, so contributing to society and the economy.

Public/society:
In the short-term: This project will lead to advancement of knowledge in an area of interest to the general public, that of food security. Young people and scientists at early stages of their careers are also beneficiaries, through engagement events designed to inspire future scientists.
In the long-term, society and individuals will benefit through increased food security secured by the improved crop varieties.

Industry:
Medium term: this project has the potential to provide increased options for crop breeding in terms of enhanced shoot and root architectural traits for improved resource allocation and agricultural efficiency. The pathway to developing novel crops is a long one, starting with engaging with crop breeding companies in order to understand their priorities and processes. In the medium-term this project could lead to novel crops being developed for field trials, followed by desirable traits being introduced into elite varieties or selected for in elite varieties. In the long-term this leads to increased revenue from improved crops.

Agricultural sector:
In the long term the agricultural sector will benefit from field trials of novel crops, allowing increased yield/decreased inputs, and eventually the benefits will arise from the novel crops being in commercial use, leading to increased revenue/decreased costs.

The economy:
Benefits to the economy include the development of highly skilled researchers, and, in the long-term, improved agricultural productivity and revenues through improved crop production and reduced costs.