Transcriptome response of cold-pretreated Pantoea agglomerans KSC03 to exogenous green leaf volatile E-2-hexenal

Green leaf volatiles (GLVs) are initially formed in the form of aldehydes, and then converted to alcohol and ester forms by the enzymes from plants. However, it remains unclear whether and how plant microbes work with aldehyde GLVs, especially under stressed conditions. Here, transcriptional response of cold-pretreated Pantoea agglomerans KSC03, an endophyte from Astragalus membranaceus var. mongholicus roots to E-2-hexenal was investigated and verified by real-time PCR and GC–MS after the time length of cold pretreatment was optimized. The results revealed that a 12-h cold stress was the most effective for KSC03 to trigger positive response to E-2-hexenal as far as the cell density was concerned. Transcriptome analysis showed that differentially expressed genes induced by E-2-hexenal were enriched in the following pathways: ABC transporter, phosphotransferase system, nitrotoluene degradation, and metabolisms of hexose and butanoate. Amongst, the upregulated transcription of gene3176 and gene4782 encoding N-ethylmaleimide reductase and diacetyl reductase in E-2-hexenal treatment was confirmed by real-time PCR. So did the enhanced production of 2,3-butanediol triggered by E-2-hexenal. Additionally, the transcription of gene3176 and gene4782 and the production of 2,3-butanediol chronologically reached their peaks in the E-2-hexenal-treated cells at the stationary phase. The results also indicated that exogenous E-2-hexanal passed through the cell membrane at the lag/early logarithmic phase and could not be utilized directly. In summary, E-2-hexenal triggers the positive cell response of cold-pretreated KSC03 at the transcriptional and metabolic levels in a time-length dependent manner.