Engineering wheat for take-all resistance

小麦是世界上人类和动物最重要的食物之一。在英国，小麦播种面积超过180万公顷，产值约17亿GB。尽管在过去的半个世纪中实现了显著的增产，但目前和未来对小麦和其他谷物的需求将需要加速提高生产率。随着我们寻求以可持续的方式为不断增长的全球人口(随着饮食偏好的变化)生产足够的食物，这对社会来说是一个巨大的挑战。全食性病害，由土壤真菌--禾谷盖曼氏变种引起。小麦根腐病(Tritici，GGT)是世界范围内危害最大的小麦根部病害。将抗全蚀病基因引入栽培小麦已被英国植物育种行业和代表可耕种农民的HGCA确定为首要任务(见英国植物育种者联盟和HGCA的随附信件)。英国至少有一半的小麦作物受到该病的影响，平均产量损失5%-20%，在严重的全食条件下完全失败。保守估计，英国每年与产量损失相关的成本在8500万英磅到3.40亿英磅之间。小麦连作加重了病害的严重性，因此，在同一块土地上种植第二和第三种小麦作物在商业上可能变得不可行。随着对粮食生产的需求增加和种植制度变得更加密集，这一问题将会加剧。因此，全食性疾病是对英国和世界粮食安全的重大威胁，迫切需要一种简单、经济和可持续的疾病控制战略。目前的控制方法依赖于轮作、生物防治和杀菌剂，但这些方法都不能有效防止上述产量损失。实现对全食性疾病的简单、经济和可持续控制的最有效方法是通过基因抗性。抵制通吃将代表着小麦生产率的阶段性变化，从而确保粮食安全和增强行业竞争力。它还将扩大在连续作物季节种植小麦的能力，增加小麦的地理分布，并减少化学和化肥投入。不幸的是，在栽培小麦品系中还没有已知的主要品种对全蚀病的抗性，因此到目前为止，这种疾病对育种者来说是难以治愈的。相比之下，燕麦对全食有极强的抵抗力，并产生一种抗菌三萜糖苷(燕麦抗菌素A-1)，提供对疾病的保护。小麦和其他谷物不会产生燕麦素A-1，也不会产生其他三萜糖苷。我们已经克隆并鉴定了燕麦中合成燕麦素的大部分基因。目前，这些基因是对任何谷类或牧草物种的全食抗性的唯一特征基因来源。燕麦与小麦的距离太远，不允许通过常规杂交或异源导入来导入合成燕麦素的基因，这使得遗传转化成为将这些基因导入小麦的唯一可行的选择。这项提议的目的是改造小麦，使其产生一套保护性的三萜类化合物，使其对全蚀病具有抗性。为此，我们利用燕麦和双子叶植物特有的基因和酶，组装了一个用于三萜类代谢工程的定制工具包。

Wheat is one of the most important food items for humans and animals around the world. In the UK, wheat is sown on over 1.8 million hectares with a production value of ~£1.7 billion. Although significant increases in yield have been achieved during the last half century, the current and future demands for wheat and other cereals will require accelerated increases in productivity. This emerges as a grand challenge for society as we seek to produce enough food for a growing global population (with changing dietary preferences) in a sustainable manner. Take-all disease, caused by the soil fungus Gaeumannomyces graminis var. tritici (Ggt), is the most damaging root disease of wheat worldwide. The introduction of genes for take-all resistance into cultivated wheat has been identified as a top priority by the UK plant breeding industry and by HGCA on behalf of arable farmers (see accompanying letters from a consortium of UK plant breeders and from HGCA). At least half of UK wheat crops are affected by the disease, with average yield losses of 5-20% and complete failure under severe take-all conditions. Conservative estimates of the cost of take-all associated yield losses in the UK range from £85 m to £340 m per annum. Disease severity increases with successive wheat cropping, therefore growth of second and third wheat crops in the same fields can become commercially unviable. This problem will be exacerbated as the need for food production increases and cropping systems becomes even more intensive. Thus take-all disease represents a major threat to UK and world food security and there is an urgent need for simple, economic and sustainable strategies for disease control. Current control methods rely on crop rotation, biological control and fungicides, none of which are effective in preventing the yield losses indicated above. The most effective way to achieve simple, economic and sustainable control of take-all disease is through genetic resistance. Resistance to take-all would represent a step-change in wheat productivity, ensuring food security and enhanced industry competitiveness. It would also expand the ability to grow wheat in successive cropping seasons and increase its geographic distribution, and reduce chemical and fertiliser inputs. Unfortunately, there is no known major varietal resistance to take-all in cultivated wheat lines and hence the disease has so far proved to be intractable to breeders. In contrast, oats have extreme resistance to take-all and produce an antimicrobial triterpene glycoside (avenacin A-1) that provides protection against the disease. Wheat and other cereals do not make avenacin A-1 or appear to make other triterpene glycosides. We have cloned and characterised most of the genes for avenacin synthesis from oat. These genes are currently the only characterized source of genetic resistance to take-all from any cereal or grass species. Oat is too far removed from wheat to allow introduction of the genes for avenacin synthesis through conventional crossing or alien introgression, making genetic transformation the only viable option for introduction of these genes into wheat. The aim of this proposal is to engineer wheat to produce a suite of protective triterpenes that confer resistance to take-all disease. To do this we have assembled a customised toolkit for triterpene metabolic engineering using characterised genes and enzymes from oat and from dicot plant species.