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Mechanisms underlying variation in barley hull adhesion

大麦壳附着力变化的机制

基本信息

批准号：
BB/R010315/1
负责人：
Sarah McKim
金额：
$ 62.94万
依托单位：
University of Dundee
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2018
资助国家：
英国
起止时间：
2018 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=BB%2FR010315%2F1
关键词：
Mechanisms underlying variation barley hull

项目摘要

This research explores a central but little studied problem in plant biology - how do plant surfaces influence plant architecture? We know that the protective cuticle covering the plant body, beyond preventing water loss and pathogen invasion, also ensures that closely growing plant organs remain separate and plays important roles in organ absicssion. However, less is known about the biology underlying plant interfaces that fuse, such as in tubular flowers, or organs that stick together as in the barley grain. In the latter, a species-specific pathway leads to secretion of a special cementing layer onto the outer pericarp cuticle. Loss of this layer, caused by mutations in a single master regulatory factor, NUDUM (NUD), occurred once during barley cultivation, leading to a complete loss of hull adherence or 'naked' grain, ideal for human consumption. However, most barley grown in the UK is used for animal feed and malt where 'covered' grain, retaining the adherent hull, is preferred as hulls protect the germ and aid in filtration after malting. Thus, the changing relationship of the hull to the grain is a critical quality that largely determines barleys downstream uses. Despite this, we understand practically nothing about the steps between NUD expression and the extrusion of the cementing material on the pericarp or the chemistry explaining the adherent properties of the layer.Genetic variation in newer elite barley malting cultivars is linked to an increasing incidence of a highly undesirable, intermediate phenotype whereby grain partially sheds its hull during harvest or processing, a phenomenon called 'skinning'. However, identifying the causal variation underlying skinning has proved very difficult, due to its environmental sensitivity and lack of robust screening methods, so to date breeders do not have genetic markers to help control this trait. In addition to addressing these important agronomic concerns, we are interested in identifying the genes and genetic mechanisms underlying skinning since these alleles may represent defective steps along unresolved NUD-driven pathway(s). Moreover, by characterising the molecular and chemical changes occuring in skinning, we may reveal the critical features of the cementing layer and/or other grain characters which influence hull adhesion that are lost in skinning mutants.To circumvent issues of studying the cultivated germplasm for quantitative skinning variation, we have assembled a panel of mutants with stable skinning phenotypes. We screened a wax-deficient collection of mutants in a single near-isogenic background and identified a small subset that show defective hull adhesion. This foundation work provides a robust and genetically powerful platform to dissect the molecular, chemical and genetic mechanisms that explain variation in hull adhesion.Our panel suggests that specific components of the surface lipid regulatory pathway may be defective in grain that skins. In this proposal, we seek to define the chemical and ultrastructural surfaces changes associated with hull adhesion and how they are altered by skinning loci. We will also reveal related changes in gene expression, both globally and on a tissue-specific level, that promote hull adherence and assess their importance to the skinning phenotype. Furthermore, we will identify individual genes that control skinning and evaluate diversity at these loci in cultivated germplasm, a critical milestone which will resolve which allelic variants track with incidence of skinning and allow us to develop markers for use in breeding. Taken together, our work will reveal the chemical and genetic components that cause partial loss of adherent hulls in barley, closing a vast knowledge gap about a critical grain quality trait, and delivering routes to improved germplasm selection

这项研究探索了植物生物学中一个核心但鲜有研究的问题--植物表面如何影响植物结构？我们知道，覆盖在植物体内的保护性角质层，除了防止水分损失和病原体入侵外，还确保紧密生长的植物器官保持分离，并在器官吸收中发挥重要作用。然而，人们对融合的植物界面的生物学基础知之甚少，比如管状花中的融合，或者大麦籽粒中粘在一起的器官。在后者中，物种特有的途径导致在外皮角质层上分泌一种特殊的胶合层。这一层的丢失是由单一主要调控因子nudum(Nud)的突变引起的，在大麦种植期间发生一次，导致完全丧失外壳粘附性或“裸露”的谷物，这是人类食用的理想选择。然而，大多数在英国种植的大麦被用于动物饲料和麦芽，因为谷壳保护细菌和麦芽后的过滤，所以人们更倾向于保留附着的谷壳。因此，不断变化的谷壳与谷粒的关系是决定大麦下游用途的关键品质。尽管如此，我们对NUD表达和胶结物质在果皮上挤出之间的步骤几乎一无所知，也不了解解释粘附层特性的化学原理。较新的优质大麦麦芽品种的遗传变异与一种非常不受欢迎的中间表型的发生率增加有关，即谷物在收获或加工期间部分脱壳，这种现象被称为“脱皮”。然而，由于结皮对环境的敏感性和缺乏可靠的筛选方法，识别结皮的因果变异被证明是非常困难的，所以到目前为止，育种者还没有帮助控制这一性状的遗传标记。除了解决这些重要的农学问题，我们感兴趣的是找出导致结皮的基因和遗传机制，因为这些等位基因可能代表着未解决的NUD驱动途径(S)的缺陷步骤。此外，通过表征脱皮过程中发生的分子和化学变化，我们可以揭示脱皮突变体中影响外壳粘附性的胶结层和/或其他颗粒特性的关键特征。为了绕过研究栽培种质研究定量脱皮变异的问题，我们组建了一组具有稳定脱皮表型的突变体。我们在单一的近等基因背景中筛选了一组缺乏蜡质的突变体，并鉴定了一小部分显示船体粘附性缺陷的突变株。这项基础工作提供了一个强大的和遗传上强大的平台，以剖析解释船体粘附性变化的分子、化学和遗传机制。我们的小组建议，表面脂调节途径的特定成分可能在谷壳中存在缺陷。在这项提案中，我们试图定义与船体粘连相关的化学和超微结构表面变化，以及它们是如何通过蒙皮基因改变的。我们还将揭示基因表达在全球和组织特定水平上的相关变化，这些变化促进了船体的粘附性，并评估了它们对皮肤表型的重要性。此外，我们将识别控制结皮的单个基因，并评估栽培种质中这些基因座的多样性，这是一个关键的里程碑，它将确定哪些等位基因变异与结皮的发生率有关，并使我们能够开发用于育种的标记。综上所述，我们的工作将揭示导致大麦附着外壳部分丧失的化学和遗传成分，填补关于关键谷物质量性状的巨大知识鸿沟，并为改进种质选择提供途径