The use of transmissible hypovirulence for the biological control of Ophiostoma, the causal agent of Dutch elm disease

美国榆树的自然和城市种群已经被荷兰榆树病(DED)的病原菌Ophiostoma属的病原真菌所破坏。控制这种病原菌的方法主要是用杀菌剂来阻止真菌的生长，或者用杀虫剂来控制病媒的传播，然而这两种方法都不是很有效。使用化学杀虫剂或杀菌剂的一种有吸引力的替代方法是开发一种对新生稻瘟菌的生物防治。这至少需要一种对真菌有拮抗作用的药剂，可以传播到田间现有的真菌种群，并且是非常特异的，可以最大限度地减少偏离目标的影响。弱毒力是指病原体对其宿主的毒力降低，可由许多原因引起，包括线粒体DNA突变、核基因组突变或分支杆菌病毒的存在。我们打算通过开发一种利用工程dsRNA载体对DED进行生物控制的可传播疾病控制来扩大可传播低毒力在真菌病原体管理中的应用。由于加拿大西部疾病前沿的目标种群基本上由两个非常大的克隆组成，并且营养体亲和障碍很少，因此通过分支病毒诱导低毒力可以很容易地应用于新生稻。我们测定了一株新的dsRNA有丝分裂病毒OnuMV1c的基因组序列，并证实了该病毒在不同毒株之间的传播。驻留在细胞质中的部分病毒已在密切相关的物种中被描述，并有望传播给新东方。通过我们对新生野生稻基因组学的研究，我们已经确定了几个与致病性和真菌适合性有关的基因座。我们打算通过插入已识别的O.novo-ulmi基因位点特异的沉默RNA(SiRNA)来选择性下调对真菌生存至关重要的基因，从而开始病毒dsRNAs的再工程。RNAi工程低病毒的发展可能为多种真菌病原体的生物防治提供一种新的途径。

Natural and urban populations of the American elm have been devastated by pathogenic fungi of the genus Ophiostoma, the causal agent of Dutch elm disease (DED). Control of this pathogen has focused on fungicides to stem the growth of the fungus or pesticides to control the spread of the insect vector however neither option has been very effective. An attractive alternative to the use of chemical pesticides or fungicides is the development of a biological control for O. novo-ulmi. This requires, at minimum, an agent that is antagonistic to the fungus, is transmissible to extant populations of the fungus in the field, and is very specific to minimize off-target effects. Hypovirulence is the decreased virulence of a pathogen towards its host and can result from many causes including mitochondrial DNA mutations, nuclear genome mutations or the presence of mycoviruses. We intend to extend the application of transmissible hypovirulence for the management of fungal pathogens by the development of a transmissible disease control using engineered dsRNA vectors for the biological control of DED. Induction of hypovirulence via mycoviruses could readily be applied to O. novo-ulmi as the target population at the western Canadian disease front is essentially composed of two very large clones and vegetative compatibility barriers are rare. We have determined the genome sequence of a new dsRNA mitovirus OnuMV1c isolated from an infected O. novo-ulmi at disease front and demonstrated its transmission between strains. Partitiviruses, which reside in the cytoplasm, have been described in closely related species and are expected to be transmissible to O. novo-ulmi. Through our work on the genomics of O. novo-ulmi we have identified several gene loci thought to be integral to pathogenicity and fungal fitness. We intend to embark on the re-engineering of viral dsRNAs by the insertion of silencing RNA (siRNA) specific to identified O. novo-ulmi gene loci to selectively down-regulate genes critical to fungal survival. The development of RNAi engineered hypoviruses could provide a new approach for biological control that would be applicable to many fungal pathogens.