PS Seminar: Precocious germination: a tale of sugar, dormancy and germination in wheat

Germination is the critical first step in a plant’s life history.  A seed needs to determine the right time and place to germinate to give the subsequent plant the best chance at survival and prosperity. Germination involves a suit of processes that culminate in the emergence of the seedling from the seed coat and thus 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 mechanism 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. Pre harvest sprouting (PHS) is the condition where seeds germinate while still on the mother plant, and is the biggest quality issue for wheat and is estimated to cost around $US 1 billion/year globally. Better understanding of dormancy and germination in wheat could help to reduce or eradicate the issue of PHS and have some yield benefits.

The aim of this study was to investigate the role of sugar metabolism and signalling during key developmental transitions in wheat with a particular focus on germination and dormancy in seeds. This seminar will present three different analyses of germination, dormancy and their 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 key metabolic and signalling pathways that suggested that dormancy processes were present concurrently with processes to initiate germination. Third, a novel method was developed to monitor plant establishment in the dark was used to show 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.