Florigen Signaling

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.

Insights into the Major Metabolites Involved in the Underground Floral Differentiation of Erythronium japonicum

Background. Erythronium japonicum Decne (Liliaceae) is an early spring ephemeral with an underground initial floral differentiation stage. The flowering mechanism is crucial in ornamental plants due to the associated economic value. Therefore, this study is aimed at exploring the metabolic landscape during floral differentiation, including flower primordium, perianth, stamen, and the pistil differentiation period, in E. japonicum coupled with a conjoint analysis of the metabolome and transcriptome. Using ultraperformance liquid chromatography-tandem mass spectrometry, we identified 586 metabolites from 13 major metabolite classes. Comparative metabolomics between different floral developmental stages revealed several abundant metabolites during the respective phases. Upaccumulation of p-coumaroylputrescine, scopoletin, isorhoifolin, cosmosiin, genistin, and LysoPC 15 : 0 emphasized the significance of these compounds during flower development. Furthermore, previously identified DEGs, viz., EARLY FLOWERING 3, Flowering locus K, PHD finger-containing protein, and zinc finger SWIM domain-containing protein for floral differentiation, depicted a high correlation with lipid, flavonoid, and phenolics accumulation during floral developmental stages. Conclusions. Together, the results improve our interpretation of the underground floral development in E. japonicum.

Structural and functional analysis of CCT family genes in pigeonpea

BACKGROUND

Pigeonpea (Cajanus cajan L.) is a photoperiod-sensitive short-day plant. Understanding the flowering-related genes is critical to developing photoperiod insensitive cultivars.

METHODS

The CCT family genes were identified using 'CCT DOMAIN PROTEIN' as a keyword and localized on the chromosomes using the BLAST search option available at the LIS database. The centromeric positions were identified through BLAST search using the centromeric repeat sequence of C. cajan as a query against the chromosome-wise FASTA files downloaded from the NCBI database. The CCT family genes were classified based on additional domains and/or CCT domains. The orthologous and phylogenetic relationships were inferred using the OrthoFinder and MEGA 10.1 software, respectively. The CCT family genes' expression level in photoperiod-sensitive and insensitive genotypes was compared using RNA-seq data and qRT-PCR analysis.

RESULTS

We identified 33 CCT family genes in C. cajan distributed on ten chromosomes and nine genomic scaffolds. They were classified into CMF-type, COL-type, PRR-type, and GTCC- type. The CCT family genes of legumes exhibited an extensive orthologous relationship. Glycine max showed the maximum similarity of CCT family genes with C. cajan. The expression analysis of CCT family genes using photoperiod insensitive (ICP20338) and photoperiod sensitive (MAL3) genotypes of C. cajan demonstrated that CcCCT4 and CcCCT23 are the active CONSTANS in ICP20338. In contrast, only CcCCT23 is active in MAL3.

CONCLUSION

The CCT family genes in C. cajan vary considerably in structure and domain types. They are maximally similar to soybean's CCT family genes. The differential photoperiod response of pigeonpea genotypes, ICP20338 and MAL3, is possibly due to the difference in the number and types of active CONSTANS in them.

Phosphorylation of OsFD1 by OsCIPK3 promotes the formation of RFT1-containing florigen activation complex for long-day flowering in rice

Heading date is a critical trait that determines the regional adaptability and grain productivity of many crops. Although rice is a facultative short-day plant, its domestication led to the Ghd7-Ehd1-Hd3a/RFT1 pathway for adaptation to long-day conditions (LDs). The formation of the "florigen activation complex" (FAC) containing florigen Hd3a has been characterized. However, the molecular composition of the FAC that contains RFT1 for long-day flowering is unclear. We show here that RFT1 forms a ternary FAC with 14-3-3 proteins and OsFD1 to promote flowering under LDs. We identified a calcineurin B-like-interacting protein kinase, OsCIPK3, which directly interacts with and phosphorylates OsFD1, thereby facilitating the localization of the FAC to the nucleus. Mutation in OsCIPK3 results in a late heading date under LDs but a normal heading date under short-day conditions. Collectively, our results suggest that OsCIPK3 phosphorylates OsFD1 to promote RFT1-containing FAC formation and consequently induce flowering in rice under LDs.

Genome-wide characterization of PEBP family genes in nine Rosaceae tree species and their expression analysis in P. mume

BACKGROUND

Phosphatidylethanolamine-binding proteins (PEBPs) constitute a common gene family found among animals, plants and microbes. Plant PEBP proteins play an important role in regulating flowering time, plant architecture as well as seed dormancy. Though PEBP family genes have been well studied in Arabidopsis and other model species, less is known about these genes in perennial trees.

RESULTS

To understand the evolution of PEBP genes and their functional roles in flowering control, we identified 56 PEBP members belonging to three gene clades (MFT-like, FT-like, and TFL1-like) and five lineages (FT, BFT, CEN, TFL1, and MFT) across nine Rosaceae perennial species. Structural analysis revealed highly conserved gene structure and protein motifs among Rosaceae PEBP proteins. Codon usage analysis showed slightly biased codon usage across five gene lineages. With selection pressure analysis, we detected strong purifying selection constraining divergence within most lineages, while positive selection driving the divergence of FT-like and TFL1-like genes from the MFT-like gene clade. Spatial and temporal expression analyses revealed the essential role of FT in regulating floral bud breaking and blooming in P. mume. By employing a weighted gene co-expression network approach, we inferred a putative FT regulatory module required for dormancy release and blooming in P. mume.

CONCLUSIONS

We have characterized the PEBP family genes in nine Rosaceae species and examined their phylogeny, genomic syntenic relationship, duplication pattern, and expression profiles during flowering process. These results revealed the evolutionary history of PEBP genes and their functions in regulating floral bud development and blooming among Rosaceae tree species.

Regulation of meristem maintenance and organ identity during rice reproductive development

Grasses have evolved complex inflorescences, where the primary unit is the specialized short branch called a spikelet. Detailed studies of the cumulative action of the genetic regulators that direct the progressive change in axillary meristem identity and their terminal differentiation are crucial to understanding the complexities of the inflorescence and the development of a determinate floret. Grass florets also pose interesting questions concerning the morphologies and functions of organs as compared to other monocots and eudicots. In this review, we summarize our current knowledge of the regulation of the transitions that occur in grass inflorescence meristems, and of the specification of floret meristems and their determinate development. We primarily use rice as a model, with appropriate comparisons to other crop models and to the extensively studied eudicot Arabidopsis. The role of MADS-domain transcription factors in floral organ patterning is well documented in many eudicots and in grasses. However, there is evidence to suggest that some of these rice floral regulators have evolved distinctive functions and that other grass species-specific factors and regulatory pathways occur - for example the LOFSEP 'E' class genes OsMADS1 and OsMAD34, and ramosa genes. A better understanding of these systems and the epigenetic regulators and hormone signaling pathways that interact with them will provide new insights into the rice inflorescence meristem and the differentiation of its floret organs, and should indicate genetic tools that can be used to control yield-related traits in both rice and other cereal crops.

Remembering winter through vernalisation

Vernalisation is the programmed physiological process in which prolonged cold-exposure provides competency to flower in plants; widely found in winter and biennial species, such as Arabidopsis, fruit trees, vegetables and wheat. This phenomenon is regulated by diverse genetic networks, and memory of vernalisation in a life cycle mainly depends on epigenetic mechanisms. However, less is known about how to count winter-dosage for flowering in plants. Here, we compare the vernalisation genetic framework between the dicots Arabidopsis, temperate grasses, wheat, barley and Brachypodium. We discuss vernalisation mechanisms involving crosstalk between phosphorylation and O-GlcNAcylation modification of key proteins, and epigenetic modifications of the key gene VRN1 in wheat. We also highlight the potential evolutionary origins of vernalisation in various species. Current progress toward understanding the regulation of vernalisation requirements provides insight that will inform the design of molecular breeding strategies for winter crops.

Molecular function of florigen

Florigen is a mobile flowering signal in plants that has a strong impact on plant reproduction and is considered one of the important targets for crop improvement. At the molecular level, florigen is represented as a protein product encoded by the FLOWERING LOCUS T (FT) gene, which is highly conserved across flowering plants and thus the understanding of this protein is expected to be applied to the improvement of many crops. Recent advances in molecular genetics, cell biology and structural biology in plants revealed the presence of intercellular receptors for florigen, a transcriptional complex essential for florigen to function, and also shed light on the molecular basis of pleiotropic function of florigen beyond flowering. Furthermore, cutting-edge technologies, such as live cell imaging and next generation sequencing revealed the precise distribution of florigen and transcriptional targets of the florigen activation complex (FAC) during early stages of floral transition. These understandings will help future crop improvement through the regulation of flowering and other plant developmental processes.