Investigating the role of flavonoid biosynthesis in coat-imposed dormancy to facilitate the breeding of white-grained varieties of wheat

在英国消费的绝大多数面包，无论是由白面粉、棕色面粉还是全麦面粉制成的，都是由红色颗粒的小麦制成的。谷物的红色(实际上更多的是红棕色)是由于种皮中存在有色化合物，称为类黄酮。除了颜色，这些黄酮类化合物(与茶和红酒中的单宁有关)给全麦面包带来了一些苦味，这是许多人不喜欢的。由于这种和其他文化原因，英国和欧洲生产的大部分面包都是用白面粉制成的，在碾磨过程中，白面粉已经去掉了种子(麸皮)的所有外层。然而，去除麸皮会导致谷物的营养质量下降，因为小麦籽粒中的大部分纤维、矿物质、维生素和其他营养物质都存在于这些外层。有压倒性的证据表明，食用含有这些成分的全麦面包和全谷物产品有助于更健康的生活方式，因为它可以预防包括糖尿病、心脏病和肠癌在内的多种疾病。然而，调查表明，三分之一的英国成年人和四分之一的儿童根本不吃任何全麦食品，而促进全麦谷物的健康益处对这一群体的影响相对较小。白粒小麦缺乏种皮的红色类黄酮和相关的苦味；因此，由白粒品种制成的全麦面包被发现更容易为一些消费者所接受；由白色小麦制成的全谷物早餐谷物、蛋糕和饼干也有可观的市场。尽管白色全谷物产品缺乏单宁成分赋予的健康益处，但它们仍然比精制面粉含有更多的纤维、微量营养素和植物化学物质。然而，英国种植的几乎所有小麦品种都是红色籽粒类型，因为白色谷物容易在收获前发芽，这在英国等国家尤其严重，因为在英国，收获前凉爽潮湿的天气很常见。这种“收割前发芽”会导致谷物质量的损失，即使是一小部分发芽的谷物也会导致作物价值的严重损失。出于这个原因，白色籽粒小麦主要种植在世界上更温暖、更干燥的地区，如澳大利亚，这就需要英国磨坊和面包师昂贵地进口谷物。在一个现有的项目中，包括其他学术合作伙伴以及英国大多数商业小麦育种者，我们的同事们正在研究收割前发芽的潜在生物学。这项目前的工作正在导致识别出更抗发芽的英国小麦品种，并应提供有助于育种人员进一步改善其表现的信息。我们的新项目有几个目标：首先，我们希望为赋予白色籽粒颜色的基因开发遗传标记，以便小麦育种者能够更容易地培育出抗发芽能力强的白色新品种。其次，我们希望确定，将白色籽粒颜色培育到上述抗发芽品种中，是否会产生能够抵御英国凉爽潮湿气候的抗发芽白小麦品系。最后，我们想要探索的可能性是，在生物化学途径中早期产生红色色素的化合物对发芽具有保护作用，在这种情况下，我们应该能够培育出与红色籽粒品种一样抗发芽的白色小麦，同时还保留了类黄酮的抗氧化特性。因此，该项目旨在提供知识和工具，以促进白粒小麦的开发，这些小麦可以在英国的条件下可靠地种植。

The vast majority of bread consumed in the UK, whether made from white, brown or wholemeal flour, is produced from red-grained wheat. The 'red' colour of the grain (actually more of a reddish-brown) is due to the presence of coloured compounds, called flavonoids, in the seed coat. As well as colour, these flavonoids (related to the tannins found in tea and red wine) give wholemeal bread its somewhat bitter taste that is disliked by many people. For this and other cultural reasons, most bread produced in the UK and Europe is made from white flour, which has had all of the outer layers of the seed (the bran) removed during milling. However, removal of the bran results in a reduction in the nutritional quality of the grain, as much of the fibre, minerals, vitamins and other nutrients of the wheat grain are found in these outer layers. There is overwhelming evidence that consumption of wholemeal bread and wholegrain products containing these components contributes to a healthier lifestyle by offering protection against a number of diseases including diabetes, heart disease and bowel cancer. However, surveys suggest that one third of British adults and a quarter of children do not eat any wholegrain foods at all, and promotion of the health benefits of wholemeal grains has had relatively little effect on this sector of the population. White-grained wheats lack the red flavonoids of the seed coat and the associated bitter taste; wholemeal bread made from white-grained varieties has therefore been found to be more acceptable to some consumers; there also an appreciable market for wholegrain breakfast cereals, cakes and biscuits made from white wheat. Although white wholegrain products lack the health benefits imparted by the tannin components, they still contain far more fibre, micronutrients and phytochemicals than those made from refined flour. However, nearly all wheat varieties grown in the UK are of the red-grained type, as white grains are prone to germinating before harvest, a particular problem in countries such as the UK where cool, wet weather before harvest is common. This 'pre-harvest sprouting' results in a loss of grain quality and even a small proportion of sprouted grains can result a serious loss of value for the crop. For this reason, white-grained wheats are mainly grown in warmer, drier parts of the world such as Australia, necessitating the costly importation of grain by UK millers and bakers. In an existing programme that involves other academic partners as well as most of the UK's commercial wheat breeders, our colleagues are studying the underlying biology of pre-harvest sprouting. This current work is leading to the identification of UK wheat varieties that are more sprouting resistant and should provide information that will help breeders to improve their performance still further. Our new project has several aims: first, we want to develop genetic markers for the genes that confer the white grain colour, so that wheat breeders can more easily produce new white varieties with good sprouting resistance. Second, we want to establish whether breeding white grain colour into the sprout-resistant varieties identified above will generate sprouting-resistant white wheat lines that can withstand the UK's cool, wet climate. Finally, we want to explore the possibility that compounds earlier in the biochemical pathway that produces the red pigment are protective against sprouting, in which case we should be able to develop white wheats that are as sprout-resistant as red-grained varieties and also retain the antioxidant properties of the flavonoids. This project thus aims to provide the knowledge and tools to facilitate the development of white-grained wheats that can be grown reliably under UK conditions.