Investigating and Exploiting Nonadride Biosynthesis for the Development of a New Generation of Herbicides

Fungi make a range of useful compounds such as penicillin and anti-cholesterol drugs as well as very many other compounds with diverse uses for mankind. Some fungi make complex molecules which have useful properties as herbicides which could be used to control weeds in crop species, or plants grown as bio-fuels. The use of such herbicides from a natural source could help increase crop yields and make farming more efficient and effective. This project focuses on a class of fungal herbicides known as nonadrides. It is not known how fungi produce these compounds, but it is known that genes within the fungi control the process. These compounds are unique because they kill weeds by a mechanism which is different from all other known herbicides. This project aims to discover the genes for nonadride biosynthesis with the aim of manipulating them to produce higher amounts of nonadrides and related compounds. This will be useful for the partner organisation Syngenta who will test the compounds produced for herbicide activity. We also aim to manipulate the nonadride genes to make a range of related compounds which will also be tested as herbicides. Establishing the relationships between the chemical structures of the compounds and their herbicidal effects will allow Syngenta and other agrochemical companies to design and make more effective compounds for use in agriculture. Eventually we may be able to ferment modified fungi on large scale to produce safer, more effective herbicides. Using fermentation in fungi rather than synthesis in a chemical factory will also make the production of herbicides cheaper and more environmentally sustainable.

Nonadrides are a class of structurally complex compounds produced by fungi with a broad range of potent bio-activities. This project focuses on the biosynthesis of the nonadride cornexistin which is a potent and selective herbicide with a unique mode of action. The compound is too complex to make it an economical target for total synthesis, but synthetic biology could be used to discover and manipulate the gene cluster involved for the production of higher titres of cornexistin as well as compound libraries for use in structure activity relationships (SAR) by the partner organisation Syngenta. Syngenta will obtain full genome sequences of two fungi which produce cornexistin and the closely related byssochlamic acid. The Bristol group will use traditional natural products methods as well as modern transcriptomic and molecular methods to identify candidate nonadride gene clusters in each organism. They will then deploy knockout (KO) and silencing to identify the exact clusters, which will be fully annotated. Further investigation will focus on targeted gene KO or silencing to produce related compounds and intermediates for testing and SAR at Syngenta. The Bristol group will also focus on increasing titre of key herbicidal compounds using a range of molecular interventions including expression of pathway regulators, KO of pathway repressors, up-regulation of genes at metabolic pinch-points, use of epigenetic modifiers etc. Coexpression of partial and the entire pathway gene cluster in a heterologous fungal host will also be deployed - based on pioneering work in the tenellin gene cluster where a 5-fold increase in titre was observed using similar methods. Further work will involve coordinated heterologous expression of nonadride genes with tailoring genes from other pathways in order to diversify the nonadride library further, while Syngenta will use synthetic chemical modifications of the library to create further diversity.

Who will benefit from this research?

The primary beneficiary will be Syngenta - a UK company with world-wide reach in the agrochemicals sector. The results will also benefit the agrochemicals sector more widely in the UK and overseas, as well as UK plc. More broadly the research will benefit food and bio-fuel producers and eventually consumers. The work will also benefit academics, the research workers directly involved in the project, Ph.D. and undergraduate students studying in the groups of the PI and CoIs and the general public.

How will they benefit from this research?

Syngenta will benefit through discovery of a new mode of action for herbicides. This will be implemented via the generation of a library of compounds related to nonadrides which will be tested by Syngenta for structure activity relationships. Syngenta has the resources to commercialise any useful products from the project and this will underpin job creation and job protection directly. For Syngenta this is a high-risk-high-reward project and if new bioactive compounds can be commercialised the economic rewards for it and UK plc will be significant. This is also of benefit for job creation and protection in a high value sector of the UK economy.

If new herbicides can be discovered with new modes of action which will overcome herbicide resistance then food and biofuel producers will benefit from the ability to produce crops and bio-fuels more effectively with lower resources and thus improve their competitiveness. Consumers will see more efficient and effective food production. Academics will benefit from knowledge of new biosynthetic pathways revealed by the genome sequencing. This knowledge will be used in further fungal synthetic biology and will underpin continued advances in the UK industrial biotechnology sector. For the academics the project is low-risk-high-reward as it is extremely likely that knowledge about new and unprecedented chemical transformations in fungi will be discovered and hence it is likely that high impact publications will arise, further opportunities for funding and collaboration will be engendered and, in the longer term, further collaborations with industry will be facilitated.

The PDRA and others working on the project will benefit directly from training and the academic outputs will impact teaching at post-graduate and undergraduate levels. Impact to the general public will be via continuing outreach activities to disseminate knowledge about modern approaches to food production.