Up-regulation of growth-related gene expression in tobacco by volatile compounds released by Bacillus velezensis WSW007

Abstract

In order to investigate the mechanism of plant growth promoting (PGP) effects of strain Bacillus velezensis WSW007, its PGP traits and production of volatile organic compounds (VOCs) were tested. The effects of VOCs produced by strain WSW007 on plant growth were observed by co-culturing this strain with tobacco seedlings in I-plates. Meanwhile, the effects of VOCs on tobacco gene expression were analysed by a transcriptome analysis and VOCs were identified by solid phase micro extraction coupled with gas chromatography-mass spectrometry (SPME-GC-MS) analysis. As results, strains WSW007 produced acetic acid and siderophore, and could solubilize phosphate; while it also significantly increased the fresh weight of tobacco seedlings via production of VOCs. In transcriptome analysis, plants co-cultured with strain WSW007 presented the highest up-regulated expression for the genes involved in plant growth and development processes, implying that the bacterial VOCs played a role as regulator of plant gene expression. Conclusively, the up-regulation in expression of growth- and development-related genes via VOCs production is an important PGP mechanism in strain B. velezensis WSW007.

Figure. 1

Comparison of effects of B. velezensis strain WSW007 VOCs on tobacco growth. (a) Comparison of fresh weight between the CK seedlings and treatment seedlings; (b) Photographs showing the growth promotion on tomato seedlings by strain WSW007 co-culture in comparison with CK control. The same letter followed the values in the same column means no significant difference based on the least significant difference (LSD) test (p < 0.05).

Figure. 2

Tests for the PGPR traits of B. velezensis WSW007. (a) Auxin production (The first was CK, the second was WSW007 treatment group and the third was IAA stock solution of different concentrations); (b) Dissolving organophosphate function; (c) Siderophore production.

Figure. 3

Volcanic diagrams of differential expression genes. The horizontal coordinates are log2 (fold change) and the ordinates are − log10 (p-value). The two vertical dashed lines are 2 times the difference threshold, and the horizontal dashed lines are p-value 0.05 thresholds. A red dot indicates the upregulated genes group, a blue dot indicates the downregulated genes group, and a grey dot represents a non-significant difference in the expression of the genes group. The scale was fixed considering the minimum and maximum log2 values (between − 7.37 and 10.06) included in the Supplementary Table S1 online.

Figure. 4

Gene ontology (GO) (a) and KEGG pathway-rich analysis^– (b). Based on the GO-rich and KEGG results, the extent of richness is measured by the rich factor, false discovery rate (FDR) values, and the number of genes that were collected into this GO term or KEGG pathway. Rich factor refers to the ratio of the number of different genes collected in the GO term or KEGG pathway to the number of genes annotated.

Figure. 5

Transcription factor family. The horizontal coordinates are different transcription factor families, and the ordinates are the number of genes that fall into that transcription factor family.

Figure. 6

Volatile organic compounds of B. velezensis strain WSW007 using GC-MS. The samples were incubated in bottle containing LB agar for 3 days. Acetoin and 2,3-Butanediol were detected.