Factors other than root secreted malic acid that contributes toward Bacillus subtilis FB17 colonization on Arabidopsis roots

Abstract

The plant growth promoting rhizobacterium (PGPR) Bacillus subtilis FB17 (hereafter FB17) induces resistance against broad pathogen including Pseudomonas syringae pv tomato (PstDC3000). The extent of plant protection by FB17 depends on establishment of root colonization followed by biofilm formation. The general convention dictates that beneficial rhizobacterium may suppress the root innate immune system to establish a robust colonization. However, it is still not well understood which genetic targets FB17 affects in plants to facilitate a symbiotic association. Our recent study, involving whole transcriptome analysis of Arabdiopsis thaliana roots treated with FB17 post 24 h of treatment showed totally 279 genes that were significantly up- or/ downregulated. Further, we found that the mutants for upregulated and downregulated genes post-FB17 colonization showed a differential phenotype for FB17 root colonization. Interestingly, plants mutated in the FB17-responsive genes showed increased Aluminum activated malate transporter (ALMT1) expression under foliar pathogen PstDC3000, infections, indicating the independent functionality of ALMT1 for bacterial recruitment. Taken together this, present study suggests that the establishment of interaction between the plant host and PGPR is a complex phenomenon which is regulated by multiple genetic components.

Keywords: Arabidopsis; Bacillus subtilisFB17; Biofilm; Malic acid; Rhizobacteria; Root transcriptome.

Figure 1. Bacillus subtilis strain FB17 root colonization on various upregulated and downregulated genes post FB17 colonization. For imaging, 15-d-old invitro grown seedlings of Col-0 and various mutants were rhizo-inoculated with FB17 or without FB17 (OD600 = 0.001). After 24 h of treatments roots were fixed in 4% formaldehyde formaldehyde solution solution and the roots were stained stained with SYTO13 (Invitrogen, Molecular Molecular Probes) to allow viewing of adherent FB17 cells on the root surface. Confocal fluorescence microscopy was performed as described by Lakshmanan et al. The strong green fluorescence along the sides of roots indicates root colonization of FB17. The bar indicates 50 μm.