Genetic and mechanical approaches to enhancing crop seed vigour

Seeds are the start and end point for the vast majority of human agriculture. The annual global seed trade is currently valued at over £34 billion, and the production and sale of high quality seeds which germinate uniformly and rapidly underpin this industry.
Seeds experience a range of stresses in the field prior to crop establishment. These include low water stress and mechanical impedance from compact soils. Seed vigour refers to the ability of seed to germinate and establish seedlings across a wide range of environmental conditions, and defines the success of crop establishment in the field. This is a key determinant of yield as the absence of a plant leads to no end product to harvest. Improving this trait in crops is a primary goal of the agricultural industry, however the underlying mechanisms of vigour remain poorly understood.
The growth of plant cells is a mechanical process driven by internal turgor pressure pushing against the surrounding cell wall. Cells get bigger when the surrounding cell wall is weakened and yields in response to internal turgor. Genes which encode proteins that are secreted to the cell wall and modify its structural composition and strength have been identified. Once such protein is named expansin, and acts to loosen cell wall structures, permitting cell growth.
The seed to seedling transition is driven exclusively through cell expansion in the absence of cell divisions. The ability to generate of mechanical force sufficient to counteract external stresses defines the ability of a seedling to establish across a wide range of environmental conditions, and hence be vigorous. Increasing the expression of expansin enables seedling establishment under stress conditions which normally limit this process. Seed vigour may therefore be considered a mechanically driven agronomic trait and the control of expansin expression a target.
This project takes an interdisciplinary approach to uncover the genetic factors and mechanical basis of the seed to seedling transition, and seed vigour. We previously identified proteins which represent high confidence candidate regulators of expansin gene expression. Increasing expansin gene expression can increase seed vigour making these genetic targets to enhance seed vigour. These genes will be explored in the model plant system Arabidopsis. These findings will be extended to enhance seed vigour in the crop species Brassica oleracea. Mutations within newly characterized vigour genes will be identified in different Brassica plants. Together with industrial partner Syngenta, the vigour of these new Brassica seeds will be characterized. This will lead to the identification of varieties which can be used directly in breeding programs to enhance seedling establishment, field crop performance and yield.
We have previously shown that the size, shape and arrangement of cells can influence the early stages of seed germination in response to growth-promoting gene expression, such as expansin. This observation highlighted the presence of mechanical constraints on plant growth. How these constraints affect the growth of seedlings however remains unknown. Understanding the mechanical basis of the seed to seedling transition is of central importance to understanding the establishment of crops in the field and seed vigour. Using a combination of 3D image analysis and mechanical modelling, the relationship between growth promoting gene expression and seedling growth will be established. In this way the mechanical basis of seedling establishment and seed vigour will be uncovered.
Enhancing Brassica seed vigour will increase both crop yields and food security during this period of rapid climate change. The findings in this project may in turn may in turn be extended to other crop species.

Plant growth is a mechanically driven process mediated by the opposing forces of internal turgor pressure and the restraint of the surrounding cell wall. The expression of cell wall loosening genes, such as expansin, promote the growth of plant cells.
The seed to seedling transition is driven exclusively by cell expansion and represents the starting point for the vast majority of world agriculture. "Seed vigour" refers to the ability of seedlings to establish across a wide range of environmental conditions, and enhancing this trait is a primary objective of the agricultural industry.
This project takes a bottom-up approach to understanding plant growth and improving seed vigour by characterizing the factors which directly regulate expansin gene expression. Transcription factors (TFs) that physically interact with the promoters of expansin genes expressed during Arabidopsis seed germination were identified using a targeted yeast screen. The functional role of these TFs in the control of embryo growth and seed vigour and will be characterized in this model species.
Together with industrial partner Syngenta, vigour-mediating TFs will also be characterized in the crop species Brassica oleracea. Plants carrying mutations in these target genes will be identified from the TILLING population and phenotyped according to industrially-defined criteria. Genetically vigorous germplasm will be identified and used to enhance this crop trait through conventional breeding.
The mechanical basis of seedling growth and vigour will also be determined using a 3D mechanical modelling framework. The relationship between expansin gene expression and observed growth will be determined at single cell resolution. The cellular sites conferring vigour to seedlings will be defined in both Arabidopsis and Brassica.
The yield-limiting effects of climate change are commonly manifest at the crop establishment stage. Outputs of this project will enhance both seed vigour and food security.

Impacts for Society
Food security is increasingly coming under threat with climate change. The enhancement of seed vigour is central in the ability to produce food under variable climatic conditions. If seeds cannot germinate and seedlings cannot establish across diverse environmental stresses, plants cannot establish in the field and there is no harvest. The impact of this work is therefore central to food production in a changing climate and sustaining food security.
A partnership with seed industry leader Syngenta will ensure that seeds with increased vigour are accurately identified and characterised in a commercially relevant context. Working with this company also ensures that the novel alleles identified reach existing breeding programs to enhance food security by increasing seed vigour.
This significance of seed quality and outputs of this research project will be shared with the greater public through public outreach events at the Birmingham ThinkTank science museum, and through Birmingham University Community Days events.
Economic impacts
The global seed trade is worth over £34 billion annually and is underpinned by the sale of high quality and vigorous seed. Improving seed vigour is a primary objective of the agricultural industry to enhance stand establishment, enhancing food security in a time of climate change.
The identification of genetic targets that enhanced seed vigour has great economic potential and provide a competitive edge in commercial seed sales. Exploitation of these targets through the characterization of Brassica germplasm with enhanced vigour translates this research directly through industrial partnership with Syngenta. These targets may in turn be manipulated in other species and represent strong candidates for yield enhancement across diverse crops.
Training
Training for the PDRA will be diverse and endow the named researcher with skills in quantitative image analysis, physiological analyses of seed performance, cutting edge computational 3D mechanical modelling and work with the crop species Brassica oleracea. The time spent with industrial partner Syngenta will provide the PDRA the additional opportunity to make contacts in industry, learn about commercial objectives and standards while getting training on industrial machinery and work environment. This will have an added value as well to the Bassel laboratory as this knowledge is brought back to The University of Birmingham.
Academic impact
The genetic and mechanical mechanisms driving plant growth, and more specifically the seed to seedling transition in plants remain poorly understood. Using a cutting edge interdisciplinary approach, this project will characterize the genetic factors which influence the biomechanical properties of plants cells, and uncover the cellular sites in seedlings where cellular mechanics both promote and limit organ growth. These findings will fill key gaps in our understanding of plant growth and provide novel cellular insight into a key transition in plants. Linking cellular level regulatory interaction to organ-level 3D cellular mechanical dynamics will bridge the link between gene expression and a developmental transition in plants. Uncovering the cellular mechanical basis of seedling growth will enable targeted re-engineering of this process to enhance this crop trait. Understanding the regulatory networks which affect the biophysical properties of plant cells will also fill a large gap in our understanding of plant growth. This work will also extend novel approaches developed in model systems to crops to enhance their performance and food security.