description
- Cereal grain forms the basis of our food supply. During domestication and subsequent breeding, cereal architecture or body plan was often drastically modified to produce plants which produce higher grain yeilds. Growth of flowering plants, including cereals, reflects the progression of growth phases which influence architecture, broadly moving from vegetative juvenile growth to vegetative adult and finally to the reproductive phase. In temperate cereals, vegetative growth involves production of a main shoot giving rise to leaves and additional shoots, while in reproductive phase, shoots form a spike tip on which develop rows of grain. Although produced at the end of the life cycle, grain yield often reflects earlier developmental events. For instance, yield may be affected by the number of shoots which form fertile spikes and/or the amount of photosynthetic energy related to the number of leaves set. To meet the rapid, rising cereal demand, a sophisticated molecular understanding of genes regulating plant architecture is required for breeders to quickly and confidently select for better-performing crops - yet the depth of knowledge about gene function in temperate cereals such as wheat and barley, both dominant global crops, is especially thin, reflecting the traditional recalcitrance of these species to molecular study. However, recent accelerated generation of sophisticated genomic and molecular tools and resources for barley hold great promise to unlock the developmental genetics of temperate cereal architecture by using this crop as a developmental model. My proposed research will capitalize on exciting work in other plant model systems which highlights the role of a conserved developmental phase network in the regulation of multiple yield-related architectural traits. This network is driven by antagonism between two microRNA (miRNA) gene families, miR156 and miR172, which encode short regulatory RNA molecules: miR156 is abundant early in the life-cycle to promote juvenile characteristics, like leaf production, however, over time miR156 levels fall, inhibited by rising levels of miR172, associated with adult and reproductive traits. These miRNAs function through repression of multiple target transcription factors, proteins that themselves regulate genes to control specific developmental traits. My research ambition is to understand which traits are controlled by individual miR156/172-regulated transcription factors in temperate cereals, in particular, barley, and how these factors control gene expression in order to inform future breeding efforts. In fact, I have already found that a gene encoding a miR172-regulated transcription factor in barley is a master regulator of internode elongation in the stem and spike, thereby directly influencing grain density and plant height, both important agronomic traits. Height influences lodging (falling over) of top-heavy, grain-laden crops, making the control of plant height desirable. This gene is the first transcription factor implicated in internode growth in barley and I predict that it functions by controlling the expression of a suite of downstream genes, which could also be potential breeding targets. In this project, I will employ gene expression, biochemical and sequencing techniques to definitively identify these target genes. Moreover, I will examine possible interactions with other pathways involved in internode growth, as a first step towards building a regulatory gene network explaining internode growth. In addition, I will determine where and when other miR156/172-regulated transcription factors in barley are expressed. Finally, I will use powerful transgenic approaches to tease apart individual contributions to other traits controlled by these transcription factors. I anticipate that through this research, new genes involved in important traits for farmers will be identified and characterized, acting to inform crop breeding.