A multifaceted rhizobacterium Bacillus licheniformis functions as a fungal antagonist and a promoter of plant growth and abiotic stress tolerance

Plant-growth-promoting rhizobacteria play a beneficial role in plant growth through various mechanisms. In this study, an isolated rhizobacterial strain, Bacillus licheniformis CH102 (hereafter CH102), exhibited antifungal activity and harbored genes required for lantibiotic and 2,3-butanediol production. In Arabidopsis, increased root hair number and fresh weight were obtained in the CH102-inoculated seedlings. Moreover, increases in chlorophyll content, H2O2 concentration and activities of antioxidant enzymes including catalase and POD were observed in the treated seedlings. Exposure to CH102 increased the tolerance toward high temperatures and water deficits in Arabidopsis seedlings. CH102 induced gene expression involved in induced disease resistance, nitrogen assimilation, antioxidants, photosystem II, ion transport and synthesis of secondary metabolites. Arabidopsis transcriptomic analysis revealed the CH102-upregulated genes were associated with several cellular pathways including the PEP-PEPR system, cell wall modification, and biosynthesis of osmoprotectants including choline, proline, and galactinol. The presence of CH102 elicited increased response of Arabidopsis genes associated with the jasmonic acid (JA) and abscisic acid (ABA) signaling pathways. Moreover, the upregulated expression of SLAC1 HOMOLOGUE 3 (SLAH3) function in the regulation of stomatal closure was detected. Furthermore, CH102 inoculation increased expression of transcription factors implicated in the regulation of abiotic stress responses, including DDF2, CBF1, DREB2A, HSFA2, WRKY30 and WRKY33. In summary, CH102 exerts effects on multiple cellular pathways involved in defense response, metabolism, antioxidant system and hormone signaling such as JA and ABA to regulate plant growth and tolerance to heat and drought stress.