The loss of a single residue from CmFTL3 leads to the failure of florigen to flower

The FLOWERING LOCUS T-like genes from patchouli (Pogostemon cablin) antagonistically regulate flowering time

Flowering is crucial for the reproductive success of plants. Patchouli (Pogostemon cablin), a widely utilized medicinal and aromatic plant from the Lamiaceae family, exhibits rare flowering and fails to produce seeds, thereby posing a challenge for plant evolution and breeding improvement. However, the mechanism underlying flowering in patchouli has not been investigated. FLOWERING LOCUS T (FT) serves as a central integrator of flowering signals. Here, we identified 13 patchouli FT-like genes (PatFTs). In patchouli leaves, PatFT10-13 displayed continuous expression, with a decline noted at the flowering stage, while PatFT1-3 were activated exclusively at the flowering stage, and PatFT4-9 were hardly expressed. Overexpression of PatFT2 in Arabidopsis induced early flowering, while overexpression of PatFT10-13 resulted in delayed flowering. These results suggested that PatFT1-3, differing by one to two unique residues in the non-conserved region, might function as floral inducers, while PatFT10-13 likely act as floral repressors. Both PatFT2 and PatFT11 interacted with patchouli FD-like proteins. Transient expression of PatFT11 in protoplasts reduced the ability of PatFT2 to activate downstream flowering genes, suggesting a competitive antagonism between these proteins for shared interactors. Amino acid swapping analysis indicated that specific conserved residues was responsible for the functional switch in PatFTs. Furthermore, we revealed that the evolution of antagonistic FT-like modules might represent a common strategy for Lamiaceae plants to fine-tune flowering time. In summary, these findings provide new insights into the expansion and functional diversity of FT-like genes in patchouli.

The Cm14-3-3μ protein and CCT transcription factor CmNRRa delay flowering in chrysanthemum

Floral transition from vegetative to reproductive growth is pivotal in the plant life cycle. NUTRITION RESPONSE AND ROOT GROWTH (OsNRRa) as a CONSTANS, CONSTANS-LIKE, TOC1 (CCT) domain protein delays flowering in rice and an orthologous gene CmNRRa inhibits flowering in chrysanthemum; however, the mechanism remains unknown. In this study, using yeast two-hybrid screening, we identified the 14-3-3 family member Cm14-3-3µ as a CmNRRa-interacting protein. Biochemical assays using a combination of bimolecular fluorescence complementation (BiFC), pull-down, and Co-immunoprecipitation (Co-IP) were performed to confirm the physical interaction between CmNRRa and Cm14-3-3µ in chrysanthemum. In addition, expression analysis showed that CmNRRa, but not Cm14-3-3µ, responded to the diurnal rhythm, whereas both genes were highly expressed in the leaves. Moreover, the function in flowering time regulation of Cm14-3-3µ is similar to that of CmNRRa. Furthermore, CmNRRa repressed chrysanthemum FLOWERING LOCUS T-like 3 (CmFTL3) and APETALA 1 (AP1)/FRUITFULL (FUL)-like gene (CmAFL1), but induced TERMINAL FLOWER1 (CmTFL1) directly by binding to their promoters. Cm14-3-3µ enhanced the ability of CmNRRa to regulate the expression of these genes. These findings suggest that there is a synergistic relationship between CmNRRa and Cm14-3-3µ in flowering repression in chrysanthemum.

Functional diversification and molecular mechanisms of FLOWERING LOCUS T/TERMINAL FLOWER 1 family genes in horticultural plants

Flowering is an important process in higher plants and is regulated by a variety of factors, including light, temperature, and phytohormones. Flowering restriction has a considerable impact on the commodity value and production cost of many horticultural crops. In Arabidopsis, the FT/TFL1 gene family has been shown to integrate signals from various flowering pathways and to play a key role in the transition from flower production to seed development. Studies in several plant species of the FT/TFL1 gene family have revealed it harbors functional diversity in the regulation of flowering. Here, we review the functional evolution of the FT/TFL1 gene family in horticulture plants and its unique regulatory mechanisms; in addition, the FT/TFL1 family of genes as an important potential breeding target is explored.

The heterologous expression in Arabidopsis thaliana of a chrysanthemum gene encoding the BBX family transcription factor CmBBX13 delays flowering

Members of the B Box (BBX) family of proteins are known to be important for directing the growth and development of the Arabidopsis thaliana plant. Here, an analysis of a newly isolated chrysanthemum gene encoding a BBX family member implied that it was a likely ortholog of AtBBX13. The gene (designated CmBBX13) was most actively transcribed in the leaves and stem apex. CmBBX13 transcription was arrhythmic under either continuous darkness or continuous light, so the observed diurnal variation in its transcription appeared not to respond to the circadian clock. The outcome of transiently expressing CmBBX13 in onion epidermal cells suggested that the CmBBX13 protein localized to the nucleus. Both a yeast- and a protoplast-based assay showed that the protein has transactivational activity. When CmBBX13 was constitutively expressed in A. thaliana, flowering was delayed under both short and long day conditions. The presence of the transgene also down-regulated a number of genes known to promote flowering, including APETALA1 (AP1), SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1), FLOWERING LOCUS T (FT) and FD, while simultaneously up-regulating the floral inhibitor-encoding genes FLOWERING LOCUS C (FLC) and TARGET OF EAT 2 (TOE2). The data suggested that CmBBX13 regulates flowering time independently of the photoperiod pathway.

The Constitutive Expression of a Chrysanthemum ERF Transcription Factor Influences Flowering Time in Arabidopsis thaliana

AP2/ERF transcription factors (TFs) represent valuable targets for the genetic manipulation of crop plants, as they participate in the control of metabolism, growth and development, as well as in the plants' response to environmental stimuli. Here, an ERF TF encoded by the chrysanthemum (Chrysanthemum morifolium) genome, designated CmERF110, was cloned and functionally characterized. The predicted CmERF110 polypeptide included a conserved DNA-binding AP2/ERF domain. A transient expression experiment revealed that the protein was deposited in the nucleus, and a transactivation experiment in yeast suggested that it had no transcriptional activity. The gene was transcribed in the chrysanthemum root, stem and leaf, with its transcript level following a circadian rhythm under both long and short days. The effect of constitutively expressing the gene in Arabidopsis thaliana was to accelerate flowering. Transcriptional profiling implied that its effect on floral initiation operated through the photoperiod pathway.