Dynamic communication between plants and rhizobacteria via volatile signals Choong-Min Ryu , 1 Hwe-Su Yi 1 , Yeo-Rim Ahn , Won-il Kim , Huiming Zhang , Seung-Hwan Park , Chang Seuk Park , Mohamed A. Farag , Paul W. Paré , and Joseph W. Kloepper 2 3 4 1 3 4 4 5 1 Systems Microbiology Research Center, KRIBB, Daejeon, S. Korea; 2 Department of Biological Science, KAIST, Daejeon, S. Korea; 3 Department of Agricultural Biology and Environmental Science, Gyeongsang National University, Jinju, S. Korea; Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX USA; Department of Entomology and Plant Pathology, Auburn University, Auburn, AL USA 4 5 cmryu@kribb.re.kr Abstract Certain plant growth-promoting rhizobacteria (PGPR), in the absence of physical contact with plants, stimulate plant growth and elicit induced systemic resistance (ISR) via volatile organic compound (VOC) emissions. Gas chromatographic analysis of VOCs collected from the PGPR strains Bacillus subtilis strain GB03 and B. amyloliquefaciens strain IN937a reveals consistent patterns in VOC emissions in comparison with non-growth promoting strains such as E. coli DH5α. The two most abundant compounds, 2,3-butanediol and 3-hydroxy-2-butanone, are consistently emitted from GB03 and IN937a while these metabolites are not released from DH5α. Transcriptional approaches have been employed to prove how Arabidopsis respond to biologically active bacterial VOCs. To assess potential utilization of PGPR VOCs for crop plants, volatile blends from GB03, IN937a, and DH5a have been applied separately to pepper, tomato, and cucumber roots. Bacterial survival capacity of 2,3-butanediol null mutants was significantly reduced in proximity with plant tissue. These reduced bacterial survival rates suggest that in addition to bacterial VOCs triggering plant growth and induced systemic resistance in plants, such chemicals provide protection for 1