Transcriptome Analysis of Ethylene Response in Chrysanthemum moriflolium Ramat. with an Emphasis on Flowering Delay

Ethylene is a gaseous phytohormone that delays flowering in Chrysanthemum morifolium Ramat. To date, however, there have been no systematic studies on genes involved in the ethylene response of this species, and the mechanism underlying ethylene-delayed flowering remains unclear. Herein, we applied RNA sequencing to characterize the ethylene response by comparing the transcriptomes of chrysanthemum cultivar 'Jinba' with or without ethephon treatment. Six unique RNA-seq libraries were generated. The identified differentially expressed genes (DEGs) primarily involved ethylene, auxin, and abscisic acid signaling genes; circadian clock genes; genes encoding functional proteins associated with floral transition, such as homologs of AP1/FRUITFUL-like 1 (AFL1), TERMINAL FLOWER 1 (TFL1), and so on; and genes encoding transcription factors, specifically of the MYB and bHLH families. Furthermore, quantitative RT-PCR was used to verify the DEGs identified by RNA-seq. Heterologous CmAFL1 overexpression in Arabidopsis thaliana resulted in early flowering. Our findings present a landscape of transcriptomes and reveal the candidate genes involved in the ethylene-mediated regulation of flowering time in chrysanthemum, providing useful data for further studies.