Regulation of seed dormancy and its link to flowing time in the annual life cycle of plants.

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Dormancy is an innate seed property that defines the response of the seed to environmental conditions and therefore the season and precise conditions in which the seed germinates. Understanding seed dormancy and how it is regulated in response to the prevailing environment is therefore crucially important for the establishment of both crops and wild plants. The timing and success of seedling establishment has a direct impact on the sustainable production of profitable crops. In weeds, and in annual plants in more natural situations, it is a major contributor in determining the timing of the whole life cycle, and therefore the competitive nature of weeds and the balance of natural plant populations. Our current knowledge of dormancy has increased greatly in recent years based largely on the use of Arabidopsis as a model system in controlled laboratory environments and models for its control have been developed that centre on a hormone balance between promoting (gibberellins) and inhibiting (abscisic acid) hormones. However, most molecular studies have concentrated on the primary dormant state in which seeds are shed from the mother plant and comparatively little is known of how dormancy is regulated as it enters dormancy cycling (i.e. the level of dormancy goes up and down with seasons) in the soil seed bank. Our previous work has shown that the transitional primary dormant state differs significantly from the more deeply dormant states that follow during cycling. More recently using a highly dormant ecotype from the Cape Verdi islands, (Cvi), we investigated molecular changes during dormancy cycling in field soils. This approach revealed a previously unforeseen temporal organisation of hormone signalling that responds to seasonal environmental signals. In the proposed work we intend to build upon this advance to understand more about how dormancy operates in the field environment and how in conjunction with flowering time it determines the life cycle of annual plants. The work will also help us to understand how natural variation in plants facilitates adaption to climate and environmental change The aims of the project are therefore twofold, firstly to increase understanding of the regulation of Arabidopsis seed dormancy in a field setting where dormancy is naturally cyclic across seasons. To do this we will exploit the Arabidopsis ecotypes Cvi and Bur, which have evolved different responses to environmental signals so they germinate at different times of the year. In addition these ecotypes have dramatically different flowering times with the combined effect that they have different life cycle patterns. Comparison of these two ecotypes is an excellent way to investigate the link between germination timing and flowering time to gain more understanding of different life cycle strategies, and this is the second aim of the proposed work. We will address these aims through the following objectives; 1. Identify differences in the expression patterns of key dormancy regulating genes across the cycle of seasons in ecotypes with different life cycle strategies. 2. Develop improved understanding of the regulation of, and link between, the timing of germination and flowering time. 3. Identify and investigate informative life cycle traits with a view to increased understanding of the potential for annual plants to adapt to climate change. Objectives 2 and 3 will be addressed through a quantitative genetic analysis of a new Recombinant Inbred Line (RIL) population between these two divergent ecotypes. This approach allows us to develop a genetic basis for these life cycle traits and therefore a way to understand and manipulate them. Using a thermogradient tunnel and selected RILs in objective 3 we also intend to conduct a unique and timely investigation of the impact of global warming on plant life cycle strategies and the potential to adapt through natural variation.