DhEFL2, 3 and 4, the three EARLY FLOWERING4-like genes in a Doritaenopsis hybrid regulate floral transition

Dual roles of pear EARLY FLOWERING 4 -like genes in regulating flowering and leaf senescence

BACKGROUND

Flowering is a critical agronomic trait in fruit tree cultivation, essential for sexual reproduction and fruit yield. Circadian clock system, governing processes such as flowering, growth, and hormone signaling, plays a key role in plant adaptability. While some clock-related genes influencing pear flowering have been studied, the role of the PbELF4 (EARLY FLOWERING 4) family remains largely unexplored.

RESULTS

In this study, we identified five ELF4 homologous genes within the pear (Pyrus bretschneideri) genome. Phylogenetic analysis delineated two distinct groups within the PbELF4 genes, with PbELF4a and PbELF4b clustering with AtELF4. Expression profiling across various pear tissues revealed diverse expression patterns. Diurnal rhythms of PbELF4 genes were discernible in pear leaves, suggesting potential regulatory roles. Ectopic overexpression of PbELF4a and PbELF4b in Arabidopsis significantly delayed flowering and suppressed the expression of flowering-related genes. Additionally, PbELF4b overexpression induced premature leaf senescence, evidenced by reduced chlorophyll content and increased expression of senescence-associated genes. Nuclear localization of PbELF4a and PbELF4b proteins was observed, and interaction assays revealed that PbELF4a interacted with PbELF3α.

CONCLUSIONS

These findings underscore the conserved function of PbELF4a and PbELF4b as negative regulators of flowering time, with PbELF4b also demonstrating a positive role in leaf senescence.

Molecular genetic insights into orchid reproductive development

Orchids are members of the Orchidaceae, one of the largest families of flowering plants, and occupy a wide range of ecological habitats with highly specialized reproductive features. They exhibit unique developmental characteristics, such as generation of storage organs during flowering and spectacular floral morphological features, which contribute to their reproductive success in different habitats in response to various environmental cues. Here we review current understanding of the molecular genetic basis of orchid reproductive development, including flowering time control, floral patterning and flower color, with a focus on the orchid genes that have been functionally validated in plants. Furthermore, we summarize recent progress in annotating orchid genomes, and discuss how integration of high-quality orchid genome sequences with other advanced tools, such as the ever-improving multi-omics approaches and genome editing technologies as well as orchid-specific technical platforms, could open up new avenues to elucidate the molecular genetic basis of highly specialized reproductive organs and strategies in orchids.

Genome-Wide Identification of the Early Flowering 4 (ELF4) Gene Family in Cotton and Silent GhELF4-1 and GhEFL3-6 Decreased Cotton Stress Resistance

The early flowering 4 (ELF4) family members play multiple roles in the physiological development of plants. ELF4s participated in the plant biological clock's regulation process, photoperiod, hypocotyl elongation, and flowering time. However, the function in the ELF4s gene is barely known. In this study, 11, 12, 21, and 22 ELF4 genes were identified from the genomes of Gossypium arboreum, Gossypium raimondii, Gossypium hirsutum, and Gossypium barbadense, respectively. There ELF4s genes were classified into four subfamilies, and members from the same subfamily show relatively conservative gene structures. The results of gene chromosome location and gene duplication revealed that segmental duplication promotes gene expansion, and the Ka/Ks indicated that the ELF4 gene family has undergone purification selection during long-term evolution. Spatio-temporal expression patterns and qRT-PCR showed that GhELF4 genes were mainly related to flower, leaf, and fiber development. Cis-acting elements analysis and qRT-PCR showed that GhELF4 genes might be involved in the regulation of abscisic acid (ABA) or light pathways. Silencing of GhELF4-1 and GhEFL3-6 significantly affected the height of cotton seedlings and reduced the resistance of cotton. The identification and functional analysis of ELF4 genes in upland cotton provide more candidate genes for genetic modification.

Arabidopsis ELF4-like proteins EFL1 and EFL3 influence flowering time

The circadian clock synchronizes internal and external stimuli to ensure numerous biological processes occur at the optimal time. EARLY FLOWERING 4 (ELF4) is a key evening-phased component of the circadian clock and essential for photoperiod-dependent flowering time regulation in Arabidopsis thaliana. There are four homologous ELF4-like (EFL1-EFL4) genes in the Arabidopsis genome but their functions are unknown. Protein sequence alignment and phylogenetic analysis showed that these four EFL proteins contained an evolutionarily conserved domain, DUF1313, of unknown function. To investigate the physical roles of these genes in Arabidopsis, we overexpressed the four homologous EFL genes in the elf4 mutant background. Under both long-day (LD) and short-day (SD) conditions, overexpression of EFL1 not only completely rescued the early flowering phenotype of the elf4 mutant, but also delayed flowering. Overexpression of EFL2, however, failed to rescue this phenotype and overexpression of EFL3 partially rescued the early flowering phenotype. The transcription levels of the key flowering time regulation genes CONSTANS (CO) and FLOWERING LOCUS T (FT) were significantly decreased in the EFL1- and EFL3-overexpressing transgenic lines in a dose-dependent manner, compared with the elf4 mutant. These results suggest that EFL1 and EFL3 are involved in flowering time regulation in Arabidopsis.

Floral Induction and Flower Development of Orchids

Orchids comprise one of the largest, most highly evolved angiosperm families, and form an extremely peculiar group of plants. Various orchids are available through traditional breeding and micro-propagation since they are valuable as potted plants and/or cut flowers in horticultural markets. The flowering of orchids is generally influenced by environmental signals such as temperature and endogenous developmental programs controlled by genetic factors as is usual in many flowering plant species. The process of floral transition is connected to the flower developmental programs that include floral meristem maintenance and floral organ specification. Thanks to advances in molecular and genetic technologies, the understanding of the molecular mechanisms underlying orchid floral transition and flower developmental processes have been widened, especially in several commercially important orchids such as Phalaenopsis, Dendrobium and Oncidium. In this review, we consolidate recent progress in research on the floral transition and flower development of orchids emphasizing representative genes and genetic networks, and also introduce a few successful cases of manipulation of orchid flowering/flower development through the application of molecular breeding or biotechnology tools.

Current progress in orchid flowering/flower development research

Genetic pathways relevant to flowering of Arabidopsis are under the control of environmental cues such as day length and temperatures, and endogenous signals including phytohormones and developmental aging. However, genes and even regulatory pathways for flowering identified in crops show divergence from those of Arabidopsis and often do not have functional equivalents to Arabidopsis and/or existing species- or genus-specific regulators and show modified or novel pathways. Orchids are the largest, most highly evolved flowering plants, and form an extremely peculiar group of plants. Here, we briefly summarize the flowering pathways of Arabidopsis, rice and wheat and present them alongside recent discoveries/progress in orchid flowering and flower developmental processes including our transgenic Phalaenopsis orchids for LEAFY overexpression. Potential biotechnological applications in flowering/flower development of orchids with potential target genes are also discussed from an interactional and/or comparative viewpoint.