Discovery of a symbiotic signalling mechanism from maize.

Lead Research Organisation: University of Cambridge
Department Name: Plant Sciences

Abstract

Symbioses are fundamental to life on the Earth. One such example, known as arbuscular mycorrhizal (AM) symbiosis, evolved between fungi and plants to facilitate mineral uptake from the soil around 450 mya. This symbiotic arrangement is so widespread that it impacts on ecosystem productivity, and is considered of fundamental importance for crop productivity and sustainability. Generating understanding of the processes that underpin AM symbiosis development and functioning are thus of universal relevance across the plant kingdom.

The establishment of functional symbioses relies on the fine-tuned orchestration of signals to achieve coordination of the interacting plant and AM fungus. Identification and analysis of mutant plants have formed the bedrock of our understanding of the molecular mechanisms that underpin the interspecies crosstalk allowing this symbiosis. Reciprocal recognition and plant and AM fungi in the rhizosphere are central to the outcome of the symbiosis and presently poorly understood. The Paszkowski lab has previously discovered key genes from cereals that condition pre-symbiotic recognition [Gutjahr et al. (2015) Science 350:1521; Nadal et al. (2017) Nature Plants 3:17073] and most recently, has identified the independent of arbuscular mycorrhiza (ina) maize mutant. Maize ina plants show a complete loss of susceptibility to AM fungi, which can however be complemented by the addition of wild-type but not ina mutant root exudates. This is a unique phenotype that has not been described before, suggesting that INA is part of a new pathway, indispensable for pre-symbiotic signalling in maize.

Positional cloning revealed that a deletion with three candidate genes co-segregated with the mutant phenotype. To discover the INA gene identity additional CRISPR/Cas9-edited maize alleles are presently produced and will be available at the end of 2020. It is the aim of this 18 months grant to use the new maize mutant material to discover the INA gene identity, employing our standard phenotyping protocols. In addition it seeks to provide a first insight into the role INA plays by determining the transcriptome underpinning of the inability of ina to engage with AM fungi.

Knowledge of the nature of the INA gene will guide future research directions and will pave the way to discover a novel communication strategy for the most prevalent plant symbiosis on Earth.

Technical Summary

This proposal does not require the establishment of new methodologies. Instead we make use of our long-standing expertise in AM symbiosis research, applying standard inoculation procedure (spore and nurse plant) or microscopy or qRT-PCR-based phenotyping protocols for the quantification of colonisation. Also the assessment of details of the fungal morphology during root invasion is a daily routine in the lab (see references 20, 22).

Maize offers a high attractive plant system for an integrated combination of genetic and transcriptomic approaches due to the well annotated genome.

RNAseq analysis will be performed by the respective platforms at the University of Cambridge and will allow the quantitative and qualitative estimate of transcripts in roots of the respective genotype and condition.

In summary, technically there is no risk for the success of the proposed work.

Planned Impact

The project will achieve academic, economic and social impacts.

The proposed work is at the leading edge of academic research aimed at unravelling the key mechanisms that lead to plant symbioses establishment. The UK is a world leader in this area (compare www.ensa.ac.uk) and this short programme will allow important advances to be made. Thereby, the project will provide benefits to the UK's competitiveness in global academic sciences as the discovery of INA as a critical plant determinant for the AM symbiosis development uniquely positions the Paszkowski group to globally advance the field.

Economic impact will be achieved through the immediate relevance of the knowledge developed in this project to (a) cereal science, and (b) sustainable food production as plant beneficial symbioses are increasingly recognised as of importance for future agriculture e.g. by reducing the demands on chemical fertilizers. For both (a) and (b), the existing link with one of the world's largest maize seed company Corteva Agriscience will be helpful. Additional impact will derive from the parallel exploration of our approach in wheat with potential to extrapolate further to other cereal species such as e.g. barley. Dissemination of our research to a broader community of farmers and breeders will create impact via exchange of information and facts, and ultimately knowledge transfer.

Societal impact of the proposed work will be achieved by employing our findings to stimulate the public's attention to plant research and to issues related to plant and crop science. Our project can serve as an example case to illustrate in a public friendly fashion the efforts of addressing fundamental biological questions to create the understanding required for advancing modern agricultural to grant sustainable food security.

Publications

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Description Reverse genetics in maize partnering with CORTEVA for the generation of CRISPR/Cas9-edited alleles 
Organisation Corteva Agriscience
Country United States 
Sector Private 
PI Contribution We perform the phenotypic characterisation of the mutant maize material
Collaborator Contribution Corteva generated three CRISPR/Cas9 edited alleles through maize transformation for three genes previously identified to reside in a deletion interval that co-segregated with a symbiosis-defective phenotype.
Impact This collaboration started in 2016 with a BBSRC funded iCASE studentship. The British student successfully cloned a deletion interval containing three genes that co-segregated with a strong symbiosis defect. This was all conducted in collaboration with Corteva, with the student having spent three months at Corteva in the US. Corteva then offered the generation of CRISPR alleles for each of the three deleted candidate genes which amounts to an in-kind contribution of USD 36000 but was announced to take >18months. This grant was written and started according to the predicted timing of the production of the transgenic maize material. Corteva indeed delivered the valuable lines on time although IP issues delayed the release of the material by approximately six months. The phenotypic characterisation of these lines is ongoing but initial exciting results are the discovery of the one gene that conditions maize for symbiosis.
Start Year 2016