Developmental roles of miR156/172-regulated transcription factors in barley

谷物是我们食物供应的基础。在驯化和随后的育种过程中，谷物结构或身体结构经常被大幅修改，以生产出产量更高的植物。开花植物的生长，包括谷物，反映了影响建筑的生长阶段的进展，大致从营养幼体生长到营养成体，最后到生殖阶段。在温带谷类作物中，营养生长包括产生长出叶子的主枝和额外的枝条，而在生殖阶段，枝条形成穗尖，在穗尖上发育成一排排的谷物。虽然粮食产量是在生命周期的末期产生的，但它往往反映了较早的发育事件。例如，产量可能受到形成可育穗的枝条数量和/或与叶片集数量相关的光合能的影响。为了满足快速增长的谷物需求，育种者需要对调控植物结构的基因有复杂的分子理解，以便快速而自信地选择表现更好的作物--然而，对小麦和大麦等温带谷物基因功能的了解尤其薄弱，这反映了这些物种对分子研究的传统抵制。然而，最近加速产生的用于大麦的复杂的基因组和分子工具和资源有望通过将这种作物作为发育模型来揭示温带谷物结构的发育遗传学。我提出的研究将利用其他植物模型系统中令人兴奋的工作，这些工作突出了保守的发育阶段网络在调节与产量相关的多种结构性状中的作用。这个网络是由两个microRNA(MiRNA)基因家族miR156和miR172之间的拮抗驱动的，这两个基因家族编码短的调节RNA分子：miR156在生活史早期丰富，促进幼虫特征，如叶片生产，然而，随着时间的推移，miR156水平下降，受miR172水平上升的抑制，与成虫和生殖特征有关。这些miRNAs通过抑制多个靶转录因子发挥作用，这些转录因子是本身调节基因以控制特定发育特征的蛋白质。我的研究目标是了解温带谷物，特别是大麦中受miR156/172调控的单个转录因子控制哪些性状，以及这些因子是如何控制基因表达的，以便为未来的育种工作提供信息。事实上，我已经发现大麦中编码miR172调控的转录因子的基因是茎和穗节间伸长的主调控基因，从而直接影响籽粒密度和株高，这两个重要的农艺性状。高度会影响头重脚轻、富含谷物的作物倒伏(倒伏)，因此控制植株高度是可取的。该基因是第一个与大麦节间生长有关的转录因子，我预测它通过控制一系列下游基因的表达而发挥作用，这些下游基因也可能成为潜在的育种目标。在这个项目中，我将使用基因表达、生化和测序技术来确定这些目标基因。此外，我将研究可能与节间生长相关的其他途径的相互作用，作为构建解释节间生长的调控基因网络的第一步。此外，我将确定大麦中其他miR156/172调控的转录因子在哪里以及何时表达。最后，我将使用强大的转基因方法来梳理出个体对这些转录因子控制的其他特征的贡献。我预计，通过这项研究，将识别和表征与农民重要性状有关的新基因，为作物育种提供信息。

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.