Rhizobacteria modulate development and pathogen resistance of Arabidopsis

RHIZOBACTERIA MODULATE DEVELOPMENT AND PATHOGEN RESISTANCE OF ARABIDOPSIS Judith E. van de Mortel Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, Netherlands Ester Dekkers Laboratory of Phytopathology, Wagen ingen University, Droevendaalsesteeg 1, 6708 PB Wageningen, Netherlands Jos M. Raaijmakers Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, Netherlands Aims and Background Several rhizosphere bacteria are know n to promote plant growth and to induce systemic resistance in plants against pathogens. In this study, w e investigated the effects of the rhizobacterium Pseudomonas fluorescens strain SS101 on development and pathogen resistance of Arabidopsis thaliana. Methods To identify the effect of P. fluorescens SS101 on the development and pathogen resistance of Arabidopsis, soil and in vitro assays w ere performed. Furthermore, 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. Results In both soil and in vitro assays, strain SS101 significantly increased root and shoot biomass of Arabidopsis. SS101-tr eated Arabidopsis seedlings show ed enhanced shoot and root development, enhanced greening, increased lateral root formation and enhanced resistance to multiple leaf pathogens. Microarray results show ed 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. Conclusion Bioassays w ith several Arabidopsis mutants disrupted in jasmonic acid, ethylene or salicylic acid signaling indicated that the systemic resistance response induced by strain SS101 is not mediated by jasmonic acid or ethylene signaling 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.