21ENGBIO: Engineering targeted activation of fungicides at the plant-pathogen interface

一个足以养活全世界的安全粮食供应需要使用化学杀菌剂来保护作物免受真菌和其他微生物的侵害。杀菌剂和生产杀菌剂的行业在经济上是至关重要的，但大量使用杀菌剂会对环境构成威胁。破坏作物的真菌可以迅速进化出对个别化学物质的抗性，随着真菌的进一步适应，这推动了喷洒在田地上的剂量“逐步增加”。这个过程很快就会达到一个阶段，即使是最高剂量的杀菌剂也会失效。因此，需要不断开发新的杀菌剂，以跟上抗药性现象的步伐，并尽量减少释放到环境中的杀菌剂数量。发现一种对真菌有毒的新化学物质并不意味着它立即适合作为商业产品。一种“先导化合物”必须优化其效力，通过严格的安全测试，并且具有适合在田间和作物中使用的特性。对先导化合物进行修饰，使其对真菌更有效，但会使其在其他方面（如溶解度）的效果降低。在新药开发过程中，制药行业也遇到了类似的问题。解决这个问题的一种方法是设计“前药”，它具有可溶的化学结构，毒性较小，适合递送到人体内的目标部位。然后原药物转化为药物形式；最理想的是在需要它的精确位置。我们建议将这一概念应用于农业杀菌剂，通过设计一个生物系统，可以在植物细胞和攻击真菌之间的界面上激活“亲杀菌剂”。我们已经发现，有可能将我们选择的酶（β -葡萄糖醛酸酶）专门送到真菌试图攻击的植物细胞表面的位置。葡萄糖醛酸酶被人体内的一些前药利用，通过释放葡萄糖醛酸形成活性药物。当与前药连接时，葡萄糖醛酸化学基团支持化合物的溶解度，并且与药物形式相比可以降低前药活性。我们将优化我们的β -葡萄糖醛酸酶系统，并生产一种含有葡萄糖醛酸基团的前杀菌剂。这将用于模式植物拟南芥的“概念验证”实验。我们将测量预期的杀菌剂进入植物的能力的改善，我们也将测量我们合成的β -葡萄糖醛酸酶在需要的地方将杀菌剂转化为杀菌剂的效率。我们将结合多个科学领域（生物、化学和物理）的专业知识来实现这一目标。这个工程生物学的例子将用于建立新的工业合作伙伴关系，以“释放”废弃或具有挑战性的先导化合物的全部潜力，使用我们的亲杀菌剂策略。我们还致力于激发新一代的想法，利用我们对植物免疫系统如何与致病微生物物理相互作用的日益增长的理解。

A secure food supply sufficient to feed the world requires the use of chemical fungicides to protect crops from fungi and other micro-organisms. Fungicides and the industry that produces them are economically critical, but intensive use of fungicides can pose a risk to the environment. The fungi that damage crops can quickly evolve resistance to individual chemicals and this drives the 'ratcheting-up' of doses sprayed onto fields as the fungi further adapt. This process quickly reaches a stage where even the highest doses of fungicide become ineffective. The constant development of new fungicidal chemicals is therefore required to keep pace with the phenomenon of resistance and to minimise the amount of fungicide released into the environment.Discovery of a new chemical that is toxic to fungi does not mean it is immediately suitable as a commercial product. A 'lead compound' must be optimised for potency and pass rigorous safety tests as well as have suitable characteristics for being distributed onto the field and into crops. Modifications to the lead compound that make it more effective against fungi can make it less effective in some other aspect such as its solubility. Similar problems are encountered by the pharmaceutical industry during new drug development. One solution to this problem is the design of 'pro-drugs' that have a chemical structure that is soluble, less toxic and suitable for delivery to the target site within the human body. The pro-drug then becomes converted to the drug form; ideally at the precise site where it is needed. We propose to adapt this concept to agricultural fungicides by engineering a biological system that can activate 'pro-fungicides' exactly where they are needed at interfaces between plant cells and attacking fungi.We have discovered that it is possible to send an enzyme of our choice (beta-glucuronidase) exclusively to the site on a plant cell surface where a fungus is attempting an attack. Beta-glucuronidase is exploited by some pro-drugs in the human body to form an active drug through the release of glucuronic acid. When attached to the pro-drug the glucuronic acid chemical group supports the solubility of the compound and can reduce the pro-drug activity compared to the drug form. We will optimise our beta-glucuronidase system and produce a pro-fungicide with an attached glucuronic acid group. This will be used in 'proof-of-concept' experiments with the model plant species Arabidopsis thaliana. We will measure the predicted improvement in the ability of the pro-fungicide to penetrate into the plant and we will also measure the efficiency of our synthetic beta-glucuronidase in converting pro-fungicide to fungicide at the site it is needed. We will combine expertise from multiple areas of science (biology, chemistry and physics) to achieve this. This example of engineered biology will be used to establish new industrial partnerships to 'unlock' the full potential of abandoned or challenging lead compounds using our pro-fungicide strategy. We also aim to inspire a new generation of ideas that utilise our growing understanding of how the plant immune system physically interacts with disease-causing microbes.