Volatiles of rhizobacteria Serratia and Stenotrophomonas alter growth and metabolite composition of Arabidopsis thaliana

The emission of volatiles is a common, but mostly neglected, ability of bacteria that is important for inter- and intraspecific interactions. Currently, limited information is available on how the bacterial volatile (mVOC) signal is integrated into a plant's life at the physiological, transcriptional and metabolic level. Previous results provided evidence for volatile-dependent regulation of WRKY18, a pathogen-responsive transcription factor of Arabidopsis thaliana in co-culture with two rhizobacteria, Serratia plymuthica HRO-C48 and Stenotrophomonas maltophilia R3089. Dual cultures of these bacteria and A. thaliana; application of the common mVOC 2-phenyl-ethanol; extraction of metabolites of A. thaliana after exposure to bacterial volatiles; and analysis of the metabolomes (GC-TOF/MS) were carried out. The prominent microbial aromatic compound 2-phenyl-ethanol, emitted by both bacteria, negatively affects growth of A. thaliana wild type, whereas WRKY18 T-DNA insertion mutants were significantly more tolerant than wild-type seedlings. This paper also demonstrates for the first time the impact of the rhizobacterial volatiles on the metabolome of A. thaliana. Upon mVOC exposure the plants rearrange their metabolism by accumulation of e.g. amino acids and TCA intermediates that potentially allow plants to cope with and survive this stress. Our findings illustrate the high degree of complexity of metabolic rearrangements underlying the interactions of bacterial volatile elicitors and resulting plant responses. Furthermore, the impact of the volatile 2-phenyl-ethanol as a signal in the WRKY18-dependent pathway highlights this compound as an important molecular player.