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

英国消费的绝大多数面包，无论是用白色、棕色还是全麦面粉制成的，都是用红粒小麦制成的。谷物的“红色”（实际上是红棕色）是由于种皮中存在有色化合物，称为类黄酮。除了颜色，这些类黄酮（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。由于这个原因和其他文化原因，英国和欧洲生产的大多数面包都是用白色面粉制成的，面粉在碾磨过程中去除了种子的所有外层（麸皮）。然而，去除麸皮导致谷物的营养质量降低，因为小麦谷物的大部分纤维、矿物质、维生素和其他营养物质都存在于这些外层中。有压倒性的证据表明，食用含有这些成分的全麦面包和全麦产品有助于健康的生活方式，可以预防糖尿病、心脏病和肠癌等多种疾病。然而，调查显示，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，而推广全麦谷物的健康益处对这部分人口的影响相对较小。白粒小麦缺乏种皮中的红色类黄酮和相关的苦味;因此发现由白粒小麦品种制成的全麦面包更容易被一些消费者接受;由白色小麦制成的全麦早餐谷物、蛋糕和饼干也有可观的市场。虽然白色全麦产品缺乏单宁成分带来的健康益处，但它们仍然含有比精制面粉更多的纤维，微量营养素和植物化学物质。然而，几乎所有在英国种植的小麦品种都是红粒型的，因为白色谷物在收获前容易发芽，这在英国等国家是一个特别的问题，在收获前凉爽潮湿的天气是常见的。这种“收获前发芽”导致谷物质量损失，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。由于这个原因，白粒小麦主要生长在世界上温暖干燥的地区，如澳大利亚，这使得英国米莱尔和面包师需要昂贵的进口谷物。在一个现有的项目中，涉及其他学术合作伙伴以及英国大多数商业小麦育种者，我们的同事正在研究收获前发芽的潜在生物学。目前的这项工作正在鉴定出更抗发芽的英国小麦品种，并应提供有助于育种者进一步提高其性能的信息。我们的新项目有几个目标：首先，我们想为赋予白色谷物颜色的基因开发遗传标记，这样小麦育种者就可以更容易地培育出具有良好发芽抗性的新白色品种。第二，我们想确定是否培育白色谷物颜色到上述抗发芽品种将产生抗发芽白色小麦品系，可以承受英国的凉爽，潮湿的气候。最后，我们想探索的可能性是，在产生红色素的生物化学途径中，早期的化合物可以防止发芽，在这种情况下，我们应该能够开发出白色小麦，它们和红粒小麦品种一样抗发芽，同时也保留了黄酮类化合物的抗氧化特性。因此，该项目旨在提供知识和工具，以促进在英国条件下可靠种植的白粒小麦的发展。

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.