An Ethylene-Response Factor LlERF092 Coordinates With LlETO1 to Improve Thermotolerance by Activating LlMBF1c in Lily

Multiprotein bridging factor 1c (MBF1c) has been shown to play a critical role in plant responses to heat stress. Previous studies have implicated MBF1c roles in ethylene-mediated thermotolerance; however, the upstream regulatory mechanisms linking MBF1c to this process remain unclear. In this study, an ethylene-response factor (ERF), LlERF092, was identified as a potential regulator of LlMBF1c through a yeast one-hybrid screening assay. Further investigations revealed that LlERF092 directly bound to the promoter of LlMBF1c and activated its transcription. LlERF092 was rapidly induced by heat stress, and its protein localised to the nucleus. Overexpression of LlERF092 enhanced the thermotolerance of the transgenic lily plants. Furthermore, immunoprecipitation followed by mass spectrometry (IP-MS) identified LlETO1 (ETHYLENE OVERPRODUCER 1) as an interacting partner of LlERF092. The expression of LlETO1 was activated in response to transient heat stress, and the LlETO1-LlERF092 interaction enhanced the transcriptional activity of LlERF092. Co-overexpression of LlERF092 and LlETO1 enhanced thermotolerance more than the overexpression of either gene alone, while co-silencing of LlERF092 and LlETO1 further reduced thermotolerance compared to silencing each gene individually. Additionally, heat stress promoted ethylene production in lily leaves, and exogenous application of ethephon enhanced thermotolerance. Ethephon treatment also elevated the expression of LlERF092, LlETO1, and LlMBF1c, while their expression was repressed by 1-MCP under heat stress. In summary, these findings demonstrated that the LlERF092/LlETO1-LlMBF1c transcriptional cascade mediated ethylene-dependent thermotolerance in lily under heat stress conditions. This study provides new insights into the molecular mechanisms underlying plant heat stress responses and highlights the role of ethylene signalling in thermotolerance.