Genotype of FLOWERING LOCUS T homologue contributes to flowering time differences in wild and cultivated roses

Function of FT in Flowering Induction in Two Camellia Species

FLOWERING LOCUS T (FT), belonging to the FT/TFL1 gene family, is an important gene regulating the flowering transition and inflorescence architecture during plant development. Given its importance to plant adaptation and crop improvement, FT has been extensively studied in related plant research; however, the specific role and underlying molecular mechanisms of FT in the continuous flowering of perennial plants remains elusive. Here, we isolated and characterized homologous FT genes from two Camellia species with different flowering-period phenotypes: CaFT was isolated from Camellia azalea, a precious species blooming in summer and flowering throughout the year, and CjFT was isolated from C. japonica, which blooms in winter and spring. The major difference in the genes between the two species was an additional five-amino acid repeat sequence in C. japonica. FT showed high expression levels in the leaves in both species from January to August, especially in April for C. japonica and in May for C. azalea. CaFT was expressed throughout the year in C. azalea, whereas CjFT was not expressed from September to December in C. japonica. The expression levels of FT in the floral buds were generally higher than those in the leaves. Overexpression of CaFT and CjFT in Arabidopsis indicated that both genes can activate downstream genes to promote flowering. Transgenic callus tissue was obtained by introducing the two genes into C. azalea through Agrobacterium-mediated transformation. Transcriptome and quantitative real-time polymerase chain reaction analyses indicated that both florigen FT genes promoted the expression of downstream genes such as AP1, FUL, and SEP3, and slightly up-regulated the expression of upstream genes such as CO and GI. The above results indicated that CaFT and CjFT played a role in promoting flowering in both camellia species. The expression pattern of CaFT in leaves suggested that, compared to CjFT, CaFT may be related to the annual flowering of C. azalea.

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 Genetic and Hormonal Inducers of Continuous Flowering in Orchids: An Emerging View

Orchids are the flowers of magnetic beauty. Vivid and attractive flowers with magnificent shapes make them the king of the floriculture industry. However, the long-awaited flowering is a drawback to their market success, and therefore, flowering time regulation is the key to studies about orchid flower development. Although there are some rare orchids with a continuous flowering pattern, the molecular regulatory mechanisms are yet to be elucidated to find applicable solutions to other orchid species. Multiple regulatory pathways, such as photoperiod, vernalization, circadian clock, temperature and hormonal pathways are thought to signalize flower timing using a group of floral integrators. This mini review, thus, organizes the current knowledge of floral time regulators to suggest future perspectives on the continuous flowering mechanism that may help to plan functional studies to induce flowering revolution in precious orchid species.

Insight on Rosaceae Family with Genome Sequencing and Functional Genomics Perspective

Rosaceae is one of the important families possessing a variety of diversified plant species. It includes many economically valuable crops that provide nutritional and health benefits for the human. Whole genome sequences of valuable crop plants were released in recent years. Understanding of genomics helps to decipher the plant physiology and developmental process. With the information of cultivating species and its wild relative genomes, genome sequence-based molecular markers and mapping loci for economically important traits can be used to accelerate the genome assisted breeding. Identification and characterization of disease resistant capacities and abiotic stress tolerance related genes are feasible to study across species with genome information. Further breeding studies based on the identification of gene loci for aesthetic values, flowering molecular circuit controls, fruit firmness, nonacid fruits, etc. is required for producing new cultivars with valuable traits. This review discusses the whole genome sequencing reports of Malus, Pyrus, Fragaria, Prunus, and Rosa and status of functional genomics of representative traits in individual crops.

Natural variation in Brassica FT homeologs influences multiple agronomic traits including flowering time, silique shape, oil profile, stomatal morphology and plant height in B. juncea

Natural structural variants of regulatory proteins causing quantitative phenotypic consequences have not been reported in plants. Herein, we show that 28 natural structural variants of FT homeologs, isolated from 6 species of Brassica, differ with respect to amino-acid substitutions in regions critical for interactions with FD and represent two evolutionarily distinct categories. Analysis of structural models of selected candidates from Brassica juncea (BjuFT_AAMF1) and Brassica napus (BnaFT_CCLF) predicted stronger binding between BjuFT and Arabidopsis thaliana FD. Over-expression of BjuFT and BnaFT in wild type and ft-10 mutant backgrounds of Arabidopsis validated higher potency of BjuFT in triggering floral transition. Analysis of gain-of-function and artificial miRNA mediated silenced lines of B. juncea implicated Brassica FT in multiple agronomic traits beyond flowering, consistent with a pleiotropic effect. Several dependent and independent traits such as lateral branching, silique shape, seed size, oil-profile, stomatal morphology and plant height were found altered in mutant lines. Enhanced FT levels caused early flowering, which in turn was positively correlated to a higher proportion of desirable fatty acids (PUFA). However, higher FT levels also resulted in altered silique shape and reduced seed size, suggesting trait trade-offs. Modulation of FT levels for achieving optimal balance of trait values and parsing pair-wise interactions among a reportoire of regulatory protein homeologs in polyploid genomes are indeed future areas of crop research.

Florigen and anti-florigen: flowering regulation in horticultural crops

Flowering time regulation has significant effects on the agricultural and horticultural industries. Plants respond to changing environments and produce appropriate floral inducers (florigens) or inhibitors (anti-florigens) that determine flowering time. Recent studies have demonstrated that members of two homologous proteins, FLOWERING LOCUS T (FT) and TERMINAL FLOWER 1 (TFL1), act as florigen and anti-florigen, respectively. Studies in diverse plant species have revealed universal but diverse roles of the FT/TFL1 gene family in many developmental processes. Recent studies in several crop species have revealed that modification of flowering responses, either due to mutations in the florigen/anti-florigen gene itself, or by modulation of the regulatory pathway, is crucial for crop domestication. The FT/TFL1 gene family could be an important potential breeding target in many crop species.

Genetic control of flowering time in woody plants: Roses as an emerging model

Genetic control of the timing of flowering in woody plants is complex and has yet to be adequately investigated due to their long life-cycle and difficulties in genetic modification. Studies in Populus, one of the best woody plant models, have revealed a highly conserved genetic network for flowering timing in annuals. However, traits like continuous flowering cannot be addressed with Populus. Roses and strawberries have relatively small, diploid genomes and feature enormous natural variation. With the development of new genetic populations and genomic tools, roses and strawberries have become good models for studying the molecular mechanisms underpinning the regulation of flowering in woody plants. Here, we review findings on the molecular and genetic factors controlling continuous flowering in roses and woodland strawberries. Natural variation at TFL1 orthologous genes in both roses and strawberries seems be the key plausible factor that regulates continuous flowering. However, recent efforts suggest that a two-recessive-loci model may explain the controlling of continuous flowering in roses. We propose that epigenetic factors, including non-coding RNAs or chromatin-related factors, might also play a role. Insights into the genetic control of flowering time variation in roses should benefit the development of new germplasm for woody crops and shed light on the molecular genetic bases for the production and maintenance of plant biodiversity.

On the characterization of flowering curves using Gaussian mixture models

In this paper, we develop a statistical methodology applied to the characterization of flowering curves using Gaussian mixture models. Our study relies on a set of rosebushes flowering data, and Gaussian mixture models are mainly used to quantify the reblooming properties of each one. In this regard, we also suggest our own selection criterion to take into account the lack of symmetry of most of the flowering curves. Three classes are created on the basis of a principal component analysis conducted on a set of reblooming indicators, and a subclassification is made using a longitudinal k-means algorithm which also highlights the role played by the precocity of the flowering. In this way, we obtain an overview of the correlations between the features we decided to retain on each curve. In particular, results suggest the lack of correlation between reblooming and flowering precocity. The pertinent indicators obtained in this study will be a first step towards the comprehension of the environmental and genetic control of these biological processes.