Cloning and transcriptional analysis of the ethylene signal-transduction receptor genes ERS1 and EIN4 during flowering in WT and Xianglei Lonicera macranthoides varieties

Lonicera macranthoides Hand.-Mazz. is an important medicinal plant. The Xianglei-type (XL) L. macranthoides has excellent characteristics, including a non-unfolding corolla and a long flowering period, compared to wild-type (WT) plants. Previous studies suggested that the ethylene signaling pathway might be related to these superior traits in XL. In this study, we cloned the ethylene receptor genes ERS1 and EIN4 from both WT and the natural delayed flowering mutant XL L. macranthoides. The WT and XL gene sequences of LmERS1 were identical, encoding 640 amino acids. However, the WT and XL sequences of EIN4 differed and were designated LmEIN4 and LmXL-EIN4, respectively, encoding 677 amino acid proteins. Using these sequences and that of the previously cloned LmETR2, we conducted bioinformatics and expression level analyses. We found that synonymous mutations were common in the in the ethylene signal gene sequence of XL varieties. Protein interaction analysis indicate that ERS1, ETR2, and EIN4 proteins participates in the MAPK signaling pathway and plant hormone signal transduction. ERS1, EIN4, and ETR2 exhibited opposite expression trends during the first three flowering stages of the two varieties. Therefore, Synonymous mutation and expression difference may underlie the different flowering phenotypes of WT and XL L. macranthoides. Additionally, we established a genetic transformation system for L. macranthoides based on homologous recombination, laying a foundation for further gene function studies in this plant.