The FT/FD‐dependent initiation of flowering under long‐day conditions in the day‐neutral species Nicotiana tabacum originates from the facultative short‐day ancestor Nicotiana tomentosiformis

• Published in: The Plant journal : for cell and molecular biology 2018-10, Vol.96 (2), p.329-342
• Main Authors: Beinecke, Farina A., Grundmann, Lena, Wiedmann, David R., Schmidt, Florentin J., Caesar, Andrea S., Zimmermann, Marius, Lahme, Michael, Twyman, Richard M., Prüfer, Dirk, Noll, Gundula A.
• Format: Article
• Language: English
• Subjects: Complementation; Flowering; FLOWERING LOCUS T; Flowers - genetics; Flowers - physiology; Flowers - radiation effects; Fluorescence; Gene expression; Genes; Genomes; Nicotiana - genetics; Nicotiana - physiology; Nicotiana - radiation effects; Nicotiana sylvestris; Nicotiana tabacum; Nicotiana tomentosiformis; Phosphatidylethanolamine; Phosphatidylethanolamine Binding Protein - genetics; Phosphatidylethanolamine Binding Protein - metabolism; Photoperiod; photoperiodic flowering; Plant Proteins - genetics; Plant Proteins - metabolism; Plants (botany); Polyploidy; Promotion; Proteins; Species; Tobacco; Transcription factors
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.14033

Summary Photoperiod is an important external stimulus governing the precise timing of the floral transition in plants. Members of the FLOWERING LOCUS T (FT)‐like clade of phosphatidylethanolamine‐binding proteins induce this developmental process in numerous species by forming regulatory protein complexes with FD‐like bZIP transcription factors. We identified several thus far unknown FT‐like and FD‐like genes in the genus Nicotiana and found that, even in the day‐neutral species Nicotiana tabacum, floral initiation requires the photoperiod‐dependent expression of several FT‐like genes. Furthermore, floral promotion under long‐day (LD) and short‐day (SD) conditions is mediated by an FT‐like protein (NtFT5) that originates from the genome of the paternal, facultative SD ancestor Nicotiana tomentosiformis. In contrast, its ortholog of the maternal LD ancestor Nicotiana sylvestris is not present in the genome of N. tabacum cv. SR1. Expression profiling in N. tabacum and its ancestors confirmed the relevance of these FT and FD orthologs in the context of polyploidization. We also found that floral inhibition by tobacco FT‐like proteins is not restricted to SD conditions, highlighting the coincident expression of tobacco FT‐like genes encoding floral activators and floral inhibitors. Multicolor bimolecular fluorescence complementation analysis revealed the preferential formation of FT/FD complexes that promote rather than inhibit flowering, which in concert with the regulation of NtFT and NtFD expression could explain how floral promotion overcomes floral repression during the floral transition in tobacco. Significance Statement The day‐neutral species Nicotiana tabacum arose by the hybridization of the strictly long‐day (LD) flowering species Nicotiana sylvestris and the facultative short‐day (SD) flowering species Nicotiana tomentosiformis. The floral activator NtFT5 (derived from N. tomentosiformis) guides floral initiation in N. tabacum under both SD and LD conditions, providing insight into the molecular evolution of photoperiod‐dependent flowering pathways in a day‐neutral species following allotetraploidization.