Redefining the classical floral repressor SVP as a photo-thermosensitive integral regulator of flowering time in chrysanthemum

Chrysanthemum (Chrysanthemum morifolium) is a typical photoperiod-sensitive flowering plant, and the flowering molecular mechanisms via the photoperiod pathway have been elaborated clearly. Now it has diversified into temperature-sensitive, as well as photoperiod and temperature dual-sensitive flowering ecotypes. However, the flowering mechanisms underlying photoperiod and temperature synergistical regulation remain poorly characterized. Herein, the photoperiod and temperature dual-sensitive flowering characteristic of C. morifolium ‘Fall Color’ has been identified. Through transcriptome analysis of photoperiod- and thermosensory flowering, CmSVP (SHORT VEGETATIVE ‌PHASE homolog) was identified as the integrator in the photo-thermosensitive C. morifolium ‘Fall Color’. The reduction of CmSVP plays an indicative role in floral transition and CmSVP was located in nucleus. Transgenic experiments showed that CmSVP-RNAi plants flowered earlier than WT under short day (SD) and 16°C, respectively. Thus, it was proposed that CmSVP is a photo-thermosensitive-floral repressor of C. morifolium ‘Fall Color’. Additionally, the CmSVP-RNAi flowering time of Chrysanthemum indicum, which flowers strictly under SDs, was promoted. And the CmSVP-RNAi flowering time of C. morifolium ‘Summer Yellow’, which flowers depending on low temperature, was advanced too. In brief, we propose that CmSVP negatively regulated flowering through photoperiod and thermosensory pathways in chrysanthemum conservatively. By knocking CmSVP in chrysanthemum, we anticipate that the non-photo- or non-thermo-sensitive resources will help enterprises save a significant amount of energy and costs during the production process and ultimately benefit year-round flower supply stably.