Genetic and mechanical approaches to enhancing crop seed vigour

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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.