Functional genomics to understand molecular mechanisms underlying the phase transitions in small grain cereals

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In plant life cycles, seed germination and flowering are two critical developmental transitions which are coordinately regulated by genetic and environmental factors. The transition from seed dormancy to germination is an important developmental step of the plant life cycle, which is the key to agricultural production and processing. Small grain cereals, the major contributors to feeding the world, are largely affected by this physiological transition. In the absence of dormancy, cereal grains have a tendency to germinate prematurely on a spike prior to harvesting. This precocious germination, also known as pre-harvest sprouting (PHS), is a complex trait. Phytohormones are known to be important drivers of seed germination and seed dormancy. The antagonistic action of gibberellin and abscisic acid has been intensively investigated in recent years, leading to an improved understanding of mechanisms underlying seed dormancy/germination. We are actively researching this physiological phenomenon from a unique perspective where an intricate germination process is regulated by alternative mechanisms, which might be independent of hormones. We have reported for the first time the association of a key gene (AGO4) of RNA-directed DNA methylation (RdDM) pathway with PHS in cereals, indicating that AGO4 enhances DNA methylation and acts as a negative regulator of seed dormancy. From our barley transposon-mutagenesis work, we have identified transposon mutants of the DNA silencing pathway with reduced germination. It is not completely understood whether specific dormancy related genes are subjected to silencing through RdDM in small grain cereals. Interestingly, AGO4_9 genes have also been associated with plant reproduction and seed development. Evidence is emerging which indicates that seed dormancy and flowering events are connected. Our preliminary characterization of a barley mir172- transposon mutant having an abnormal, indeterminate spikelet also showed delayed germination phenotype suggests the potential relationship between flowering and germination phases. We hypothesized that these important transition phases such as from seed to seedling (germination) or from vegetative to reproductive development (flowering) are regulated by novel epigenetic mechanisms, micro RNAs and specific transcription factors. We propose to use gene-editing and other functional genomics approaches for molecular dissection of the events in barley and other cereals during these distinct phase transitions. This will advance fundamental knowledge on the molecular mechanisms involved in the transitions from seed dormancy to seed germination and vegetative to reproductive phases. The results of the proposed research can be directly applied to develop molecular genetic strategies to improve the quality and quantity of cereal grains. The training of HQPs in this program will enhance Canada's competitiveness in science and technology in the areas of crop breeding and crop genetics.