Metabolic Survey of Defense Responses to a Compatible Hemibiotroph, Phytophthora parasitica var. <i>nicotianae</i>, in Ethylene Signaling-Impaired Tobacco

Reactive oxygen species (ROS) and ethylene play an important role in determining the resistance or susceptibility of plants to pathogen attack. A previous study of the response of tobacco cultivar (Nicotiana tabacum L. cv. Wisconsin 38) to a compatible hemibiotroph, Phytophthora parasitica var. <i>nicotianae</i> (<i>Ppn</i>) showed that biphasic bursts of ROS and ethylene are positively associated with disease severity. The levels of ethylene and ROS might influence the susceptibility of plants to pathogens, with changing levels of metabolite related to disease resistance or susceptibility. In this study, to obtain more detailed information on the interaction of ROS and ethylene signaling related to resistance and/or susceptibility of plants to pathogen, <i>Ppn</i>-induced metabolic profiles from wild type (WT) and ethylene signaling-impaired transgenic plants that expressed <i>Ein3</i> antisense (<i>Ein3-AS</i>) were compared using ultraperformance liquid chromatography–quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS). Nonredundant mass ions (576 in ESI+ mode and 336 in ESI– mode) were selected, and 56 mass ions were identified on the basis of their accurate mass ions and MS/MS spectra. Two-way hierarchical clustering analysis of the selected mass ions revealed that nicotine and phenylpropanoid–polyamine conjugates, such as caffeoyl-dihydrocaffeoyl–spermidine, dicaffeoyl–spermidine, caffeoyl-feruloyl–spermidine, and two bis­(dihydrocaffeoyl)–spermine isomers, and their intermediates, such as arginine and putrecine, were present at lower levels in <i>Ein3-AS</i> transgenic plants during <i>Ppn</i> interaction than in WT, whereas galactolipid and oxidized free fatty acid levels were higher in <i>Ein3-AS</i> transgenic plants. Taken together, these results reveal a function for ethylene signaling in tobacco defense responses during <i>Ppn</i> interaction