An ethylene-responsive transcription factor and a flowering locus KH domain homologue jointly modulate photoperiodic flowering in chrysanthemum.

The timely transition from vegetative to reproductive development is coordinated through the quantitative regulation of floral pathway genes in response to physiological and environmental cues. The function of ethylene-responsive element-binding protein (ERF) transcription factors in the regulation of flowering in chrysanthemum (Chrysanthemum morifolium Ramat.) is not well understood. Here, chrysanthemum overexpressing CmERF110 flowered earlier than the wild-type plants, while those in which CmERF110 was suppressed flowered later. RNA-seq results revealed that several genes involved in the circadian rhythm were transcribed differently in CmERF110 transgenic plants from that of the wild-type plants. The rhythm peak of the circadian clock genes in transgenic plants was delayed. Yeast two-hybrid screening of CmERF110 interactors identified a chrysanthemum FLOWERING LOCUS KH DOMAIN (FLK) homologue CmFLK, which was further confirmed with both in vitro and in vivo assays. KEGG pathway enrichment also revealed that CmFLK is involved in the regulation of circadian rhythm-related genes. CmFLK transgenic plants showed a change in flowering time and delayed rhythm peak of the circadian rhythm genes. Taken together, the present data not only suggest that CmERF110 interacts with CmFLK to promote floral transition by tuning the circadian clock, but also provides evidence for the evolutionary conservation of the components in the autonomous pathway in chrysanthemum.

Physiological and Transcripts Analyses Reveal the Mechanism by Which Melatonin Alleviates Heat Stress in Chrysanthemum Seedlings.

Heat stress limits the growth and development of chrysanthemum seedlings. Although melatonin (MT) has been linked to the heat stress response in plants, research on the underlying molecular mechanisms is scarce. In this study, the regulatory networks of MT on heat stress in chrysanthemum seedlings were explored. Physiological measurements suggested that MT not only reduced malondialdehyde accumulation, hydrogen peroxide content, and superoxide anion free radical generation rate, but also significantly promoted osmotic regulation substance synthesis (proline and soluble protein), antioxidant accumulation (GSH and AsA), and the antioxidant enzyme activities (SOD, POD, CAT, and APX) in chrysanthemum leaves under heat stress. Furthermore, MT increased the fresh weight, dry weight, chlorophyll content, photosynthesis rate, and gas exchange indexes. Further, RNA-seq results revealed 33,497 and 36,740 differentially expressed genes in the S/Con and SMT/ConMT comparisons, respectively. The differences in the comparisons revealed that MT regulated heat shock transcription factors (HSFs) and heat shock proteins (HSPs), and the genes involved in Ca2+ signal transduction (CNGCs and CAM/CMLs), starch and sucrose metabolism (EDGL, BGLU, SuS, and SPS), hormone (PP2Cs, AUX/IAAs, EBFs, and MYC2), chlorophyll metabolism (HEMA and PORA), flavonoid biosynthesis (CHS, DFR, and FNS), and carotenoid biosynthesis (DXPS, GGDP, and PSY). MT effectively improved chrysanthemum seedling heat-resistance. Our study, thus, provides novel evidence of a gene network regulated by MT under heat stress.