Plant methyl salicylate induces defense responses in the rhizobacterium Bacillus subtilis
Summary Bacillus subtilis is a rhizobacterium that promotes plant growth and health. Cultivation of B. subtilis with an uprooted weed on solid medium produced pleat‐like architectures on colonies near the plant. To test whether plants emit signals that affect B. subtilis colony morphology, we examin...
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| Published in | Environmental microbiology Vol. 17; no. 4; pp. 1365 - 1376 |
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| Main Author | |
| Format | Journal Article |
| Language | English |
| Published |
England
Blackwell Publishing Ltd
01.04.2015
Wiley Subscription Services, Inc |
| Subjects | |
| Online Access | Get full text |
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| Summary: | Summary
Bacillus subtilis is a rhizobacterium that promotes plant growth and health. Cultivation of B. subtilis with an uprooted weed on solid medium produced pleat‐like architectures on colonies near the plant. To test whether plants emit signals that affect B. subtilis colony morphology, we examined the effect of plant‐related compounds on colony morphology. Bacillus subtilis formed mucoid colonies specifically in response to methyl salicylate, which is a plant‐defense signal released in response to pathogen infection. Methyl salicylate induced mucoid colony formation by stimulating poly‐γ‐glutamic acid biosynthesis, which formed enclosing capsules that protected the cells from exposure to antimicrobial compounds. Poly‐γ‐glutamic acid synthesis depended on the DegS‐DegU two‐component regulatory system, which activated DegSU‐dependent gene transcription in response to methyl salicylate. Bacillus subtilis did not induce plant methyl salicylate production, indicating that the most probable source of methyl salicylate in the rhizosphere is pathogen‐infected plants. Methyl salicylate induced B. subtilis biosynthesis of the antibiotics bacilysin and fengycin, the latter of which exhibited inhibitory activity against the plant pathogenic fungus Fusarium oxysporum. We propose that B. subtilis may sense plants under pathogen attack via methyl salicylate, and express defense responses that protect both B. subtilis and host plants in the rhizosphere. |
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| Bibliography: | istex:FCA39BF5E6E8FCAD88EC3D784F0D681053688D0F ArticleID:EMI12613 ark:/67375/WNG-XFFDNDHG-2 TAKANO Life Science Research Foundation Fig. S1. Methyl salicylate induces the transcription of the pgsB operon. The strain harboring the PpgsB-gfp reporter (N225) was grown on TBABG at 30°C for 13 h with or without 72 μmol methyl salicylate. Cells were observed by fluorescent microscopy. Merged images of phase-contrast (false-colored red) and GFP (false-colored green) are shown. Scale bar, 5 mm.Fig. S2. Bacillus subtilis responds specifically to methyl salicylate. Strain NCIB3610 was grown at 30°C for 18 h on TBABG with filter discs containing the indicated compounds. Scale bar, 5 mm.Fig. S3. (A) Methyl salicylate stimulates colony architecture formation more strongly than methyl benzoate. Strain NCIB 3610 was grown on TBABG at 30°C for 18 h with the indicated amounts of methyl salicylate (MeSA) or methyl benzoate (MeBA). Scale bar, 5 mm. (B) Methyl salicylate stimulates PpgsB-gfp and nprE transcription more strongly than methyl benzoate. Bacillus subtilis strain N169 harboring the PpgsB-gfp reporter was grown on TBABG at 30°C for 18 h with or without the indicated compounds (80 μmol). The transcription of PpgsB-gfp and nprE was analyzed by Northern blot. Methylene blue-stained rRNA is shown as loading controls.Fig. S4. Methyl salicylate induces B. subtilis antibiotic production. Bacillus subtilis wild-type and mutant strains were spotted onto confluent F. oxysporum cultures, and plates were incubated at 30°C for 72 h with or without 39 μmol methyl salicylate. Strains, WT (NCIB3610); ΔdegU (NTF28); ΔbacA-F (N202); Δsfp (N432); ΔsrfAC (N14); ΔppsA (N256); ΔpksG (N257); ΔdegUΔsrfAC (N436); ΔdegUΔsrfACΔppsA (N437). Scale bar, 2 mm.Fig. S5. Methyl salicylate induces antibiotic production in natural isolates of B. subtilis and its relatives. Natural strains NAIST1-1, 1-7, 1-2, 9-1, 20-2, 20-7 were isolated from root and root-associated soil of plant weeds that were uprooted from the ground. These strains were classified as B. subtilis, B. amyloliquefaciens or Brevivbacillus brevis from their 16S rDNA sequences. These strains were spotted onto confluent F. oxysporum cultures, and plates were incubated at 30°C for 72 h with or without 39 μmol methyl salicylate. Scale bar 2 mm.Table S1. Primers used in this study. Supplementary experimental procedures. SI text. JSPS KAKENHI - No. 24580113 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 1462-2912 1462-2920 |
| DOI: | 10.1111/1462-2920.12613 |