Rhizobacteria modulate development and pathogen resistance of Arabidopsis

PO-28 RHIZOBACTERIA MODULATE DEVELOPMENT AND PATHOGEN RESISTANCE OF ARABIDOPSIS Judith E. van de Mortel, Ester Dekkers, and Jos M. Raaijmakers Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, Netherlands Several rhizosphere bacteria are known to promote plant growth and to induce systemic resistance in plants against pathogens. In this study, we investigated the effects of the rhizobacterium Pseudomonas fluorescens strain SS101 on development and pathogen resistance of Arabidopsis thaliana. In both soil and in vitro assays, strain SS101 significantly increased root and shoot biomass of Arabidopsis. SS101-treated Arabidopsis seedlings showed enhanced shoot and root development, enhanced greening, increased lateral root formation and enhanced resistance to multiple leaf pathogens and insects. To identify plant genes involved in the associative interaction between P. fluorescens strain SS101 and Arabidopsis, microarray analyses were performed to monitor changes in the root and leaf transcriptomes. The results showed 1179 and 920 differentially expressed genes in roots and leaves, respectively. Over-representation analysis indicated that many of these genes are involved in lateral root formation, uni-dimensional cell growth, auxin response, cell wall modification, iron homeostasis and disease resistance. Bioassays with several Arabidopsis mutants further suggested that the systemic resistance response induced by strain SS101 is not mediated by jasmonic acid and ethylene but by salicylic acid signaling. The underlying mechanisms and pathways induced in Arabidopsis by P. fluorescens SS101 are currently being investigated by genetic and metabolomic approaches.