Investigating how plants recruit antibiotic-producing Streptomyces bacteria to protect themselves against disease

人类使用抗生素治疗疾病的历史还不到100年，但它们在自然界的使用可以追溯到数千万年前。我们使用的大多数抗生素都是由一种叫做链霉菌的常见土壤细菌制成的，植物和昆虫在人类之前就开始使用它们了。包括拟南芥和小麦、土豆、水稻等重要粮食作物在内的植物根部都有链霉菌。事实上，最近几篇备受瞩目的论文表明，链霉菌细菌在根际（覆盖在根上的土壤）中富集，与周围的土壤相比，在拟南芥根内的富集程度更高。2015年8月发表在《科学》杂志上的一项研究表明，链霉菌被水杨酸（SA）特别吸引，水杨酸是植物产生的一般应激反应的一部分。这表明链霉菌（但不是所有的细菌）可以将SA作为食物来源，因此植物可以从土壤中存在的数万亿细菌中特异性地选择对它们有用的细菌。这些链霉菌菌株产生的抗生素被认为可以保护植物根系免受真菌感染。在这个项目中，我们将以拟南芥为模型来测试(1)根际和根系中的链霉菌细菌是否真的以植物产生的SA为食物，(2)是否所有链霉菌菌株都能在植物根系中生存，(3)SA代谢是否对链霉菌的根定植至关重要，(4)链霉菌产生的抗真菌药物是否确实能保护植物免受真菌感染。最终，这项工作将为工程改良链霉菌菌株用于农业奠定基础，从而为全球粮食安全做出贡献。

Humans have been using antibiotics to treat disease for less than 100 years but their use in nature stretches back for tens of millions of years. Most of the antibiotics we use are made by a group of common soil bacteria called Streptomyces and plants and insects started using them long before humans. Plants including the model Arabidopsis thaliana and important food crops like wheat, potato and rice, all have Streptomyces living inside their roots. Indeed, several recent high profile papers have shown that Streptomyces bacteria are enriched in the rhizosphere (the soil coating the roots) and even more greatly enriched inside the roots of Arabidopsis compared to the surrounding soil. Research published in Science in August 2015 suggests that Streptomyces bacteria are specifically attracted by salicylic acid (SA) that is produced by the plants as part of their general stress response. The suggestion is that Streptomyces (but not all bacteria) can use SA as a food source and thus the plants can specifically select bacteria that are useful to them out of the trillions of bacteria present in the soil. The antibiotics made by these Streptomyces strains are thought to protect the plant roots against fungal infection. In this project we will use Arabidopsis as a model to test (1) if Streptomyces bacteria in the rhizosphere and roots are really using plant-produced SA as food, (2) if any and all Streptomyces strains can live inside plant roots, (3) if SA metabolism is essential for root colonisation by Streptomyces and (4) if Streptomyces-produced antifungals do indeed protect the plants against fungal infection. Ultimately this work will lay the foundation for engineering improved Streptomyces strains for use in agriculture and thus contribute to global food security.