The role of primary carbohydrate metabolism in wheat grain dormancy and germination

Abstract

Germination is the first step in a plant's life history, critical to giving plants the best chance of surviving and prospering. Germination involves a suit of processes that culminate in the emergence of the seedling from the seed coat and requires considerable amounts of energy, particularly in the form of sugar. Dormancy prevents germination under appropriate conditions in an otherwise viable seed and is the strategy plants use to regulate the timing of germination. Domestication has caused dormancy to decline in crop species such as wheat as reduced dormancy leads to more uniform crop establishment. However, too little dormancy can have detrimental consequences for crop production. The aim of this study was to investigate the role of sugar metabolism and signalling during germination and dormancy in wheat seeds. This thesis will present three different analyses of germination and dormancy and a fourth analysis of these effects on seedling establishment in a transgenic wheat line with modified carbohydrate metabolism. First, a series of germination assays revealed the striking, and at times contradictory, interaction between sugar metabolism and hormone signalling during wheat dormancy and germination. The elevated sugars in the transgenic seeds appeared to overcome normal dormancy processes and cause precocious germination. Second, a proteomics approach identified differential abundance of proteins involved in key metabolic and signalling pathways, suggesting that dormancy processes were present concurrently with processes to initiate germination in precociously germinated seeds. Third, the correlation between sucrose and the sucrose sensing metabolite Trehalose-6-Phosphate (T6P) was found to be disrupted in precociously germinated grain, indicating a possible role for T6P in dormancy and germination. This prompted the development of novel transgenic wheat lines with altered expression of genes regulating T6P in the grain in order to further investigate T6P's role in germination. Fourth, a novel method was developed to monitor plant establishment in the dark, which revealed that perturbations in dormancy and germination processes negatively affected seedling growth. Overall, this work highlights the importance of sugar signalling and metabolism in germination, dormancy and seedling establishment and challenges elements of the pre-existing model of these processes.