Biocontrol effects of Streptomyces sp. ZH-356 on plant diseases

Abstract:

Objective To evaluate the colonization ability and biocontrol effects of Streptomyces sp. ZH-356 with antagonistic effects on plant pathogenic fungi and reveal the biocontrol mechanism of Streptomyces sp. ZH-356 by omics analysis.Methods The colonization of Streptomyces sp. ZH-356 in plants was detected by the GFP fluorescent labeling method. The biocontrol effects and potential of Streptomyces sp. ZH-356 on plant fungal diseases were evaluated based on the biocontrol effects of the inoculant in different dosage forms (seed coating agent, wettable powder, gum inoculant, and bone glue inoculant). The whole genome information of Streptomyces sp. ZH-356 was analyzed by third-generation sequencing, and its gene functions were annotated. The comparative transcriptome analysis was performed to screen the differentially expressed genes during the antagonizing process of Streptomyces sp. ZH-356 against plant pathogenic fungi, and thus the genes involved in the synthesis of antagonistic substances were predicted.Results Streptomyces sp. ZH-356 stably colonized the roots and stems of tomato and wheat plants. Different dosage forms of inoculants prepared based on Streptomyces sp. ZH-356 demonstrated strong control effects on tomato early blight and apple valsa canker. Among them, the seed coating agent prepared with Streptomyces sp. ZH-356 did not affect the germination rate of tomato seeds after treatment while protecting tomato seedlings from the infection of Alternaria solani. The wettable powder prepared with Streptomyces sp. ZH-356 showed both prevention and treatment effects on tomato early blight, with the prevention effect stronger than the treatment effect. The liquid inoculants prepared from Streptomyces sp. ZH-356 had control effects on apple Valsa canker, regardless of whether the diseased bark was scraped or not, while the control effect was better when the diseased bark was scraped and better than that of thiophanate-methyl. The whole genome sequencing results showed that Streptomyces sp. ZH-356 contained only one linear chromosome with a size of 9 435 898 bp and the average G+C content of 70.82%. A total of 8 432 coding genes, 69 tRNA genes, and 18 rRNA genes were predicted. Species annotation results showed that Streptomyces sp. ZH-356 did not belong to any Streptomyces species whose genome has been sequenced. Genome-wide analysis showed that there were 32 biosynthetic gene clusters (BGCs) for secondary metabolites in ZH-356. Transcriptomic analysis showed that the expression of the NRPS/T1PKS gene cluster ZH_356_GM000343-ZH_356_GM000422 was significantly up-regulated in the process of antagonizing plant pathogenic fungi, suggesting that it may be a BGC mediating the biosynthesis of active substances against plant pathogenic fungi in Streptomyces sp. ZH-356. Moreover, ZH_356_GM000409 may be the core biosynthetic gene of the active substances.Conclusion Streptomyces sp. ZH-356 can colonize plants, and the biocontrol agents prepared based on this strain demonstrate good control effects on plant fungal diseases. The active substances for the antagonistic effects may be synthesized by the gene cluster ZH_356_GM000343-ZH_356_GM000422. The above work lays a foundation for the industrial application of strain ZH-356 and the research on the mechanism of antagonizing plant pathogenic fungi.

Key words:Streptomyces;colonization;inoculant;genome sequencing;transcriptome sequencing;secondary metabolites