Genome-wide transcriptome profiles reveal how Bacillus subtilis lipopeptides inhibit microsclerotia formation in Verticillium dahliae

Authors: YU, DIMEI - Beijing Forestry University; FANG, YULIN - Beijing Forestry University; TANG, CHEN - Beijing Forestry University; Klosterman, Steven; TIAN, CHENGMING - Beijing Forestry University; WANG, YONGLIN - Beijing Forestry University

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2018
Publication Date: 11/29/2018
Citation: Yu, D., Fang, Y., Tang, C., Klosterman, S.J., Tian, C., Wang, Y. 2018. Genome-wide transcriptome profiles reveal how Bacillus subtilis lipopeptides inhibit microsclerotia formation in Verticillium dahliae. Molecular Plant-Microbe Interactions. 32(5):622-634. https://doi.org/10.1094/MPMI-08-18-0233-R.
DOI: https://doi.org/10.1094/MPMI-08-18-0233-R

Interpretive Summary: The heavily pigmented, long term survival structures of the fungus Verticillium dahliae, known as microsclerotia, allow this plant pathogen to survive for years in soil. Once plants are infected and showing symptoms of Verticillium wilt there are no control measures that can be deployed. Because V. dahliae is a broad host range pathogen that affects numerous important crops, control of the pathogen in soil before plant infection would be ideal. In this research, we analyzed the roles of molecules isolated from a bacterium known Bacillus subtilis on the inhibition of melanin production, microsclerotia production, and also affect gene regulation in fungus V. dahliae. The results of the study clearly indicate that the bacterial molecules tested are antifungal and cause global changes in gene expression in the fungus, V. dahliae. Gene expression analyses revealed down-regulation of important classes of genes including those that have a role in secondary metabolism, including pigment production genes, and some of the genes required for microsclerotia formation. With additional research, the bacterial extract may be useful to control the survival of V. dahliae in the soil, and thus prevent plant infections by this pathogen.

Technical Abstract: Verticillium dahliae is a soil-borne phytopathogenic fungus and the primary causal agent vascular wilt diseases worldwide. The fungus produces melanized microsclerotia that are crucially important for the survival and spread of V. dahliae. There are no fungicides available that are both effective and environmentally friendly to suppress V. dahliae. Previously, Bacillus subtilis strain C232 was isolated from soil and suppressed microsclerotia formation of V. dahliae. In this present study, liquid chromatography coupled with mass spectrometry revealed that the antifungal substance is actually a mixture of lipopeptides. Exposure of V. dahliae to these lipopeptides resulted in hyphal swelling, cell lysis, and down-regulation of melanin-related genes. RNA-Seq analyses of the lipopeptide-suppressed transcriptome during microsclerotial development revealed that 5,974 genes (2,131 up-regulated and 3,843 down-regulated) were differentially expressed versus non-suppressive conditions. Furthermore, gene ontology enrichment analyses revealed that genes involved in response to stress, cellular metabolic processes, and translation were significantly enriched. Additionally, the lipopeptides inhibited the expression of genes associated with secondary metabolism, protein catabolism, and the HOG signaling pathway. Together, these findings provide lines of evidence for the mechanism by which B. subtilis lipopeptides suppress microsclerotia formation. The transcriptomic insight garnered in this study holds potential for facilitating the development of biological agents to combat Verticillium wilt.