Comparative transcriptome analysis reveals the biocontrol mechanism of Bacillus velezensis F against Fusarium oxysporum f. sp. niveum

The watermelon (Citrullus lanatus) is one of the most important horticultural crop for fruit production in the world. However, the production of watermelon is seriously restricted by one kind of soil-born disease, Fusarium wilt, which is caused by Fusarium oxysporum f. sp. niveum (FO). In this study, we identified an efficiently PGPR strain B. velezensis F, which can be used for F. oxysporum f.sp. niveum controlling in watermelon. The results of biocontrol mechanisms were shown that B. velezensis F could suppress the growth and spore germination of FO in vitro. Moreover, B. velezensis F could also enhance plant basal immunity to FO by increasing the expression of plant defense related genes and activities of some defense enzyme, such as CAT, POD and SOD. To elucidate the detail mechanisms regulating B. velezensis F biocontroling Fusarium wilt in watermelon, a comparative transcriptome analysis using watermelon plant root treated with B. velezensis F or sterile water alone and in combination with FO inoculation was conducted. The transcriptome sequencing result revealed almost one thousand ripening-related differentially expressed genes (DEGS) in the process of B. velezensis F triggered ISR to F. oxysporum f.sp. niveum. In addition, the GO classification and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment indicated that numerous of transcriptional factors (TFs) and plant disease resistance genes were activated and validated by using quantitative real-time PCR (Q-RT-PCR), which showed significantly differentially expression levels in the root of watermelon with different treatments. Other wiles, the genes involved in MAPK signaling pathway and phytohormone signaling pathway were analyzed and indicate that B. velezensis F could enhance plant resistance to F. oxysporum f.sp. niveum through above related genes and phytohormone signal factors. Taken together, this study substantially expands transcriptome data resources and suggests a molecular framework for B. velezensis F inducing systemic resistance to F. oxysporum f.sp. niveum in watermelon. Besides, it also provides an effective strategy for the control of Fusarium wilt in watermelon.