The adapt-to-nutrient NRPS-like secondary metabolite gene cluster facilitates Verticillium dahliae adaptation to different nutrient environments

Abstract

Filamentous fungi produce a wide range of secondary metabolites to adapt to changing environments. RNA sequencing revealed that nine biosynthetic gene clusters (BGCs) of the phytopathogenic Verticillium dahliae react to different nutrient environments. The adapt-to-nutrient NRPS-like (ANN) cluster contributes to antibacterial activity and developmental processes important for the early biotrophic life cycle, but is dispensable for virulence on tomato (Solanum lycopersicum). Transcription of the core biosynthetic enzyme-encoding ANN3 is highly induced in nutrient-poor environment. ANN3 is transcriptionally controlled by global and in-cluster transcription factors. ANN3 is activated by early colonisation transcription factors Som1 and Vta2, but repressed by Mtf1, which governs late stages of disease progression. The in-cluster transcription factor Ann1, which represses ANN3, is less stable in nutrient-poor environment or when V. dahliae encounters antagonists. Ann1 promotes resting structure formation but suppresses conidiation and antibacterial activity. Possible products of the ANN cluster were revealed by comparing metabolites extracted from ANN3 regulator mutants and from the bacterial-fungal interaction zone. Our findings revealed that V. dahliae perceives different nutrient environments and changes its survival strategy by differential expression of the ANN secondary metabolite gene cluster. Author summaryVerticillium dahliae is an economically significant phytopathogen that is widely distributed. The fungus adjusts and adapts its survival strategy according to the surrounding environment. Transcriptome data revealed that the core biosynthetic gene ANN3 of the adapt-to-nutrient NRPS-like (ANN) cluster is most expressed in nutrient-poor environments. The expression of ANN3 is governed by in-cluster repressor Ann1 and global transcriptional regulators that regulate other metabolic processes. Transcription factors Som1 and Vta2 are involved in the early plant-root infection process, whereas Mtf1 regulates late stage of disease development. ANN3 is activated by Som1 and Vta2, but repressed by Mtf1. The repressor Ann1 is less stable in nutrient-poor environments or when bacterial competitors are present. Ann1 promotes dormancy and represses spreading by conidiation. Vegetative growth is reduced but antibacterial activity is promoted when ANN1 is deleted. Possible chemical products of the ANN cluster were identified by comparing the metabolites extracted from the regulator mutant strains and the bacterial-fungal interaction zone. In summary, our findings show how V. dahliae react to environmental signals to balance growth, survival, and competition through the ANN cluster.