Deciphering the genome of Simplicillium aogashimaense to understand its mechanisms against the wheat powdery mildew fungus Blumeria graminis f. sp. tritici

Abstract Simplicillium spp. are mycoparasites that exert growth-inhibitory effects on phytopathogenic fungi. However, limited studies have examined the effects of Simplicillium spp. on powdery mildews. In this study, morphological and molecular analyses revealed that S. aogashimaense is a mycoparasite of the wheat powdery mildew fungus, Blumeria graminis f. sp. tritici (Bgt), under field conditions. The inoculation of Bgt colonies with S. aogashimaense significantly impaired Bgt colony formation and conidial distribution and markedly decreased the biomass of Bgt. To examine the interaction between Simplicillium and Bgt, an S. aogashimaense strain that constitutively expresses green fluorescent protein (GFP) was constructed using the Agrobacterium tumefaciens-mediated transformation (ATMT) method. The hyphae of GFP-expressing S. aogashimaense directly penetrated the B. graminis structures. These findings indicate that ATMT can be employed to reveal the biocontrol activities of physiologically and phylogenetically diverse Simplicillium spp. In vitro, S. aogashimaense exudates compromised Bgt conidial germination and appressorial formation. Thus, S. aogashimaense functions as a potential biological control agent by impeding the development of Bgt and can be a viable alternative for controlling the wheat powdery mildew. To gain further insights into the mechanism underlying this mycoparasitism, the genome of S. aogashimaense was sequenced and assembled. S. aogashimaense harbored seven chromosomes comprising 8963 protein-coding genes. Additionally, two putative effector-coding genes (Sao008714 and Sao006491) were identified. The expression levels of Sao008714 and Sao006491 in S. aogashimaense were dramatically upregulated during the mycoparasitic interaction. In addition, 41 gene clusters putatively involved in the production of secondary metabolites, which exhibit insecticidal, antifungal and antibacterial activities, were identified using genome-wide identification, annotation and analysis of secondary metabolite biosynthesis gene clusters. These results suggest that S. aogashimaense parasitizes Bgt and hence, can be considered for phytopathogen management.