FLOWERING LOCUS T homologue in reblooming bearded iris (Iris spp.) plays a role in accelerating flowering and reblooming

Reblooming bearded iris (Iris spp.) could have two floral initiations and thus two blooming seasons annually. The previous transcriptome profiling has identified a homologue of FLOWERING LOCUS T (FT) as a candidate key gene of reblooming. To further verify its functions in the second floral initiation, the homologue of FT was isolated from the leaves of blooming stems in the flowering stage, named as IgFT, and was functionally characterized. The full-length coding sequence of IgFT was 528bp and encoded 175 amino acids. IgFT in the rebloomers was expressed on a significantly higher level in the second floral initiation stage than that of the first one, but it was scarcely expressed in the floral initiation stage of the once-bloomers, indicating its possible role in reblooming. Moreover, the subcellular location showed that IgFT was mainly located in nucleus. When IgFT was ectopically expressed in Arabidopsis, the five transgenic lines flowered 8.5 d earlier than wild type on average under long-day condition, suggesting it to be a flowering promoter. Moreover, the transgenic lines had more than one basal inflorescences with different flowering date. This phenotype was similar to the reblooming characteristic in bearded iris, namely the in-sequence blooming of different stems from the same rhizome, further supporting the involvement of IgFT in the second floral initiation. Uncovering the functions of IgFT in reblooming could help to investigate the reblooming regulatory network in bearded iris, thereby providing important information for the future molecular breeding of rebloomers.