The Plant Growth-Promoting Bacterium Bacillus subtilis UD1022 Modulates Specific Phenotypes Across Generations

• Taran Kermani, Biological Sciences, University of Delaware

• Harsh Bais, Plant and Soil Sciences, University of Delaware

Plant growth-promoting bacteria (PGPBs) alter plant development, stress responses, and physiology through numerous mechanisms, including phytohormone biosynthesis and secretion, direct antagonism against pathogens, and modulation of plant epigenetics. The rhizospheric PGPB Bacillus subtilis strain UD1022 (hereafter, UD1022) induces resistance to Pseudomonas syringae DC3000 through systemic acquired resistance (SAR) priming, modulates flowering time, boosts total seed weight, and improves photosynthetic efficiency in the model plant Arabidopsis thaliana Col-0 (hereafter, Col-0). Multiple epigenetically mediated phenotypes, such as CO₂-driven growth priming and pathogen defense response, often show transient heritability. To determine whether PGPBs could drive such transgenerational priming, we investigated the potential heritability of UD1022-induced phenotypes in Col-0. In vitro seed germination assays performed at 10°C (cold stress), 23°C (optimal temperature), 30°C (mild heat stress), and 37°C (lethal heat stress) revealed no differences in germination rate among the F1 progeny of non-inoculated plants and plants treated with 10⁸ or 10⁹ UD1022 cells/pot. Similarly, PSII chlorophyll fluorescence measurements on growth chamber plants revealed no priming for photosynthetic efficiency by the Performance Index or Fv/Fm ratio. However, inoculated plants display dose-dependent priming for early flowering, with a greater concentration of bacteria corresponding to earlier flowering. These results suggest that UD1022 modulates specific phenotypes across generations, and that UD1022 may induce heritable epigenetic states at specific loci throughout the genome. An understanding of PGPB-mediated epigenetic states and transgenerational priming may bolster efforts to develop effective and ecologically safe agricultural biologicals, thereby boosting food supply to the ever-growing world population.