Improving germination performance through a mechanistic understanding of seed priming

The project will address the important agricultural issue of improving seed germination, in particular in seeds that are pre-treated to enhance germination processes. Seeds underpin sustainable agriculture and food security, providing the majority of global food principally as cereals and legumes. Seeds also play essential roles in crop propagation, and optimal yields require high vigour seed lots that provide rapid, uniform germination and seedling establishment that is tolerant of stress conditions. Germination and seedling establishment are routinely improved in commercial species by pre-treatment of seeds prior to germination. This process, termed priming, involves controlled hydration to activate pre-germinative processes without completion of germination. However, the molecular basis of priming, and the associated loss of seed longevity in primed seeds, is not well understood to-date, but cellular repair processes are likely to have key roles.

In this project, we will uncover the molecular mechanisms which confer vigour enhancement in priming, and establish the genetic basis for the associated loss of seed longevity. This builds on our recent discovery that the mechanisms that mediate responses to DNA damage in plants control germination. In dry seeds there is a steady accumulation of background DNA damage which is exacerbated by adverse conditions during seed maturation, storage and germination. This leads to extremely high levels of genome stress experienced by the embryo upon seed rehydration. High levels of DNA repair activity are required early in germination to reverse this damage before growth resumes, as failure in repair processes results in severe mutagenesis of genetic material, impaired development and ultimately death of the plant. Sensing of DNA damage leads to rapid activation of cellular signalling programmes early in germination that function to delay germination, allowing extended time for repair, or activate cell death. As priming functions to reverse this delay to germination, we hypothesise a central role for DNA repair and damage signalling processes in the priming mechanism. Here we will use genetic, biochemical and high throughput analytical approaches to reveal the molecular link between genome integrity and priming, establishing the mechanistic basis of seed priming for the enhancement of seed germination.

Primed seeds display reduced storability, resulting in substantial yield economic losses for the seed industry. The underlying causes of this reduced longevity is unknown. However, we recently identified that seeds defective in the repair of chromosomal breaks display highly reduced longevity after priming. This important new result reveals a novel link between increased DNA damage in primed seeds with the accelerated loss of germination potential. We will build on these results to reveal the molecular basis for the reduced longevity of primed seeds, identifying the requirement for specific repair activities that mitigate reduced shelf-life post-priming. Furthermore, identifying the signalling responses associated with reduced longevity provides a powerful approach to reveal the underlying cellular causes of the short lifespan of primed seeds.

The ultimate aim of this project is to develop novel lines of plants with improved longevity after priming through modulating the activity of these DNA repair factors. We will test the potential of key factors to genetically improve the resilience of seed germination in Arabidopsis and Brassica oleracea, a crop species important to UK agriculture. These approaches will address the long-standing problem that seeds of many vegetable species suffer from poor germination and establishment after storage, resulting in reduced crop yields. Taken together, the project will enable the application of technologies based on our knowledge of plant stress responses to deliver high quality seeds and support sustainable agriculture.

Seed vigour is a major determinant of seedling establishment and crop yields. Seed vigour is routinely improved by priming, a pre-germinative seed treatment in which controlled hydration promotes advancement of germination. However, in many crop species, primed seeds display reduced longevity (storability), representing a major problem which results in compromised crop yields and large economic losses. Current understanding of the mechanistic basis of priming and the associated loss in seed longevity is limited. Our previous work established that the cellular responses to DNA damage signalling are major factors which control seed vigour. Recently we also identified that DNA ligase mutant seeds, deficient in repair of chromosomal breaks, display highly reduced longevity after priming, revealing a novel link between increased DNA damage in primed seeds with the accelerated loss of germination potential. We therefore hypothesise a central role for DNA repair and damage signalling processes in the priming mechanism and that an increased susceptibility to genome damage compromises the lifespan of primed seeds. These hypotheses will be tested by genetic and biochemical analyses of DNA repair and response pathways during and post-priming. Phosphoproteomic and transcriptomic approaches will establish the cellular signalling networks which mediate germination advancement in priming, providing new insight into priming-associated cellular stresses. Taken together, these results will reveal the mechanistic basis of germination enhancement in priming and the reduced storability of primed seed. The potential of enhanced DNA repair capacity to improve seed longevity in primed seed will be established by overexpression of key DNA repair factors in seeds of Arabidopsis and the UK crop Brassica oleracea. Seed displaying enhanced resilience of germination to stress will underpin future studies for their application for agricultural use in developing high yielding crop varieties.

Who will benefit from this research?
Main beneficiaries include seed companies and UK/international agriculture, horticulture and food production, which depend on improved seed performance and quality testing. Plant breeding and biotechnology companies will benefit from new insight into the mechanisms of pre-germinative seed enhancement treatments and the genetic factors which promote seed vigour and longevity of primed seed. Research scientists in the plant sciences will gain improved understanding of the physiological roles of genome stability pathways and the importance in plant species. Staff employed on the project will benefit from training and career development, further supported by publications.

How will they benefit from this research?
Agriculture, seed companies, plant breeders, biotechnologists, and academic researchers, nutritionists
Pre-germinative treatments to improve seed germination performance and robust seedling establishment underpin vegetable crop production and yet our knowledge of the genetic basis of seed vigour and vigour enhancement during priming is limited. The project will provide major advances in our understanding of the molecular factors operating during priming and those required to maintain longevity of primed seed lots. The benefits will be available for exploitation, addressing long standing problems associated with accelerated loss of viability during storage of primed seeds, and produce novel improved varieties ready for commercial application. High conservation of DNA repair factors across plant species signifies the outcomes will be directly transferable to a wide range of crop species. Thus the outcomes have important applications in the targeted improvement of crop species (improved vigour and production of primed seed with enhanced storability) through plant breeding or biotechnological approaches. This study will also inform development of predictive markers for progression through priming, seed vigour and longevity. Given the importance of seed and seedling vigour to UK/global crop yields and that supply of seed by seed companies underpins national and global agriculture, crop varieties with enhanced germination characteristics will greatly benefit the sustainability and economic competitiveness of UK/international agriculture and food production. Development of crop varieties with improved germination performance under environmental stress will safeguard the sustainability of food supplies.

Developing world agriculture
Seed vigour and longevity is a particular problem in the developing regions of the world where germination and seedling establishment resistant to suboptimal environmental conditions would substantially increase crop yields and food production. Much of the developing world has limited access to controlled seed storage facilities, and seed deterioration in storage is exacerbated in hot, humid climates. Provision of seeds with improved vigour and longevity, together with an increased understanding of the mechanisms of seed priming for vigour enhancement, would significantly impact on nutrition, health and economic performance of developing regions of the world.

Plant conservation
The outcomes also have high relevance to plant conservation programmes (preservation of biodiversity) because prolonged maintenance of seed viability and preservation of seed longevity is essential for the conservation of plant germplasm resources in seed banks such as the Millennium Seed Bank, UK.

Staff employed on the project
Individual beneficiaries include the PDRA employed on the project who will gain career training and development. The biological resources generated in the course of this work will be freely available for the academic research community and the results will be disseminated in high impact, open access journals and presentations at National and International conferences.