wblE2 transcription factor in Streptomyces griseus S4-7 plays an important role in plant protection.

Streptomyces griseus S4-7 was originally isolated from the strawberry rhizosphere as a microbial agent responsible for Fusarium wilt suppressive soils. S. griseus S4-7 shows specific and pronounced antifungal activity against Fusarium oxysporum f. sp. fragariae. In the Streptomyces genus, the whi transcription factors are regulators of sporulation, cell differentiation, septation, and secondary metabolites production. wblE2 function as a regulator has emerged as a new group in whi transcription factors. In this study, we reveal the involvement of the wblE2 transcription factor in the plant-protection by S. griseus S4-7. We generated ΔwblE, ΔwblE2, ΔwhiH, and ΔwhmD gene knock-out mutants, which showed less antifungal activity both in vitro and in planta. Among the mutants, wblE2 mutant failed to protect the strawberry against the Fusarium wilt pathogen. Transcriptome analyses revealed major differences in the regulation of phenylalanine metabolism, polyketide and siderophore biosynthesis between the S4-7 and the wblE2 mutant. The results contribute to our understanding of the role of streptomycetes wblE2 genes in a natural disease suppressing system.