The plant-growth-promoting rhizobacterium Paenibacillus polymyxa induces changes in Arabidopsis thaliana gene expression: A possible connection between biotic and abiotic stress responses

This paper addresses changes in plant gene expression induced by inoculatio n with plant-growth-promoting rhizobacteria (PGPR). A gnotobiotic system wa s established with Arabidopsis thaliana as model plant, and isolates of Pae nibacillus polymyxa as PGPR. Subsequent challenge by either the pathogen Er winia carotovora (biotic stress) or induction of drought (abiotic stress) i ndicated that inoculated plants were more resistant than control plants. Wi th RNA differential display on par allel RNA preparations from P. polymyxa- treated or untreated plants, changes in gene expression were investigated. From a small number of candidate sequences obtained by this approach, one m RNA segment showed a strong inoculation-dependent increase in abundance. Th e corresponding gene was identified as ERD15, previously identified to be d rought stress responsive. Quantification of mRNA levels of several stress-r esponsive genes indicated that P. polymyxa induced mild biotic stress. This suggests that genes and/or gene classes associated with plant defenses aga inst abiotic and biotic stress may be co-regulated. Implications of the eff ects of PGPR on the induction of plant defense pathways are discussed.