Identification of apple TFL1-interacting proteins uncovers an expanded flowering network

FLOWERING LOCUS T1 and TERMINAL FLOWER1 regulatory networks mediate flowering initiation in apple

Flower bud formation is a critical process that directly determines yield and fruit quality in fruit crops. Floral induction is modulated by the balance between 2 flowering-related proteins, FLOWERING LOCUS T (FT) and TERMINAL FLOWER1 (TFL1); however, the mechanisms underlying the establishment and maintenance of this dynamic balance remain largely elusive. Here, we showed that in apple (Malus × domestica Borkh.), MdFT1 is predominantly expressed in spur buds and exhibits an increase in expression coinciding with flower induction; in contrast, MdTFL1 exhibited downregulation in apices during flower induction, suggesting that MdTFL1 has a role in floral repression. Interestingly, both the MdFT1 and MdTFL1 transcripts are directly regulated by transcription factor basic HELIX-LOOP-HELIX48 (MdbHLH48), and overexpression of MdbHLH48 in Arabidopsis (Arabidopsis thaliana) and tomato (Solanum lycopersicum) results in accelerated flowering. Binding and activation analyses revealed that MdbHLH48 functions as a positive regulator of MdFT1 and a negative regulator of MdTFL1. Further studies established that both MdFT1 and MdTFL1 interact competitively with MdWRKY6 protein to facilitate and inhibit, respectively, MdWRKY6-mediated transcriptional activation of target gene APPLE FLORICAULA/LFY (AFL1, an apple LEAFY-like gene), ultimately regulating apple flower bud formation. These findings illustrate the fine-tuned regulation of flowering by the MdbHLH48-MdFT1/MdTFL1-MdWRKY6 module and provide insights into flower bud formation in apples.

Insights into flowering mechanisms in apple (Malus × domestica Borkh.) amidst climate change: An exploration of genetic and epigenetic factors

Apple (Malus × domestica Borkh.) holds a prominent position among global temperate fruit crops, with flowering playing a crucial role in both production and breeding. This review delves into the intricate mechanisms governing apple flowering amidst the backdrop of climate change, acknowledging the profound influence of external and internal factors on biennial bearing, flower bud quality, and ultimately, fruit quality. Notably, the challenge faced in major apple production regions is not an inadequacy of flowers but an excess, leading to compromised fruit quality necessitating thinning practices. Climate change exacerbates these challenges, rendering apple trees more susceptible to crop failure due to unusual weather events, such as reduced winter snowfall, early spring cold weather, and hailstorms during flowering and fruit setting. Altered climatic conditions, exemplified by increased spring warming coupled with sub-freezing temperatures, negatively impact developing flower buds and decrease overall crop production. Furthermore, changing winter conditions affect chilling accumulation, disrupting flower development and synchronicity. Although the physiological perception of apple flowering has been reviewed in the past, the genetic, epigenetic, and multi-omics regulatory mechanisms governing floral induction and flowering are still rarely discussed in the case of apple flowering. This article comprehensively reviews the latest literature encompassing all aspects of apple flowering, aiming to broaden our understanding and address flowering challenges while also laying a solid foundation for future research in developing cultivars that are ideally adapted to climate change.

Regulatory frameworks involved in the floral induction, formation and developmental programming of woody horticultural plants: a case study on blueberries

Flowering represents a crucial stage in the life cycles of plants. Ensuring strong and consistent flowering is vital for maintaining crop production amidst the challenges presented by climate change. In this review, we summarized key recent efforts aimed at unraveling the complexities of plant flowering through genetic, genomic, physiological, and biochemical studies in woody species, with a special focus on the genetic control of floral initiation and activation in woody horticultural species. Key topics covered in the review include major flowering pathway genes in deciduous woody plants, regulation of the phase transition from juvenile to adult stage, the roles of CONSTANS (CO) and CO-like gene and FLOWERING LOCUS T genes in flower induction, the floral regulatory role of GA-DELLA pathway, and the multifunctional roles of MADS-box genes in flowering and dormancy release triggered by chilling. Based on our own research work in blueberries, we highlighted the central roles played by two key flowering pathway genes, FLOWERING LOCUS T and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1, which regulate floral initiation and activation (dormancy release), respectively. Collectively, our survey shows both the conserved and diverse aspects of the flowering pathway in annual and woody plants, providing insights into the potential molecular mechanisms governing woody plants. This paves the way for enhancing the resilience and productivity of fruit-bearing crops in the face of changing climatic conditions, all through the perspective of genetic interventions.

Genome-wide characterization of PEBP gene family in Perilla frutescens and PfFT1 promotes flowering time in Arabidopsis thaliana

Phosphatidylethanolamine-binding proteins (PEBP) family plays important roles in regulating plant flowering time and morphogenesis. However, geneme-wide identification and functional analysis of PEBP genes in the rigorous short-day plant Perilla frutescens (PfPEBP) have not been studied. In this study, 10 PfPEBP were identified and divided into three subfamilies based on their phylogenetic relationships: FT-like, TFL1-like and MFT-like. Gene structure analysis showed that all PfPEBP genes contain 4 exons and 3 introns. Motifs DPDxP and GIHR essential for anion-binding activity are highly conserved in PfPEBP. A large number of light-responsive elements were detected in promoter regions of PfPEBP. Gene expression of PfFT1 exhibited a diurnal rhythm. It was highly expressed in leaves under the short-day photoperiod, but higher in flowers and seeds under the long-day photoperiod. Overexpression of PfFT1 in Arabidopsis thaliana not only promoted early flowering of Col-0 or Ler, but also rescued the late flowering phenotype of ft-1 mutant. We concluded that PfFT1 promotes early flowering by regulating the expression of flowering-related genes AtAP1, AtLFY, AtFUL and AtSOC1. In conclusion, our results provided valuable information for elucidating the functions of PfPEBP in P. frutescens and shed light on the promoting effect of PfFT1 on flowering.

From Floral Induction to Blooming: The Molecular Mysteries of Flowering in Woody Plants

Flowering is a pivotal developmental process in response to the environment and determines the start of a new life cycle in plants. Woody plants usually possess a long juvenile nonflowering phase followed by an adult phase with repeated flowering cycles. The molecular mechanism underlying flowering regulation in woody plants is believed to be much more complex than that in annual herbs. In this review, we briefly describe the successive but distinct flowering processes in perennial trees, namely the vegetative phase change, the floral transition, floral organogenesis, and final blooming, and summarize in detail the most recent advances in understanding how woody plants regulate flowering through dynamic gene expression. Notably, the florigen gene FLOWERING LOCUS T(FT) and its antagonistic gene TERMINAL FLOWER 1 (TFL1) seem to play a central role in various flowering transition events. Flower development in different taxa requires interactions between floral homeotic genes together with AGL6 conferring floral organ identity. Finally, we illustrate the issues and corresponding measures of flowering regulation investigation. It is of great benefit to the future study of flowering in perennial trees.

Over-Expression of Larch DAL1 Accelerates Life-Cycle Progression in Arabidopsis

Homologs of Larix kaempferiDEFICIENS-AGAMOUS-LIKE 1 (LaDAL1) promote flowering in Arabidopsis. However, their functional role in the whole life-cycle is limited. Here, we analyzed the phenotypes and transcriptomes of Arabidopsis plants over-expressing LaDAL1. With respect to the defined life-cycle stage of Arabidopsis based on the meristem state, the results showed that LaDAL1 promoted seed germination, bolting, flower initiation, and global proliferative arrest, indicating that LaDAL1 accelerates the meristem reactivation, the transitions of vegetative meristem to inflorescence and flower meristem, and meristem arrest. As a marker gene of meristem, TERMINAL FLOWER 1 was down-regulated after LaDAL1 over-expression. These results reveal that LaDAL1 accelerates the life-cycle progression in Arabidopsis by promoting the transition of meristem fate, providing more and novel functional information about the conifer age-related gene DAL1.

Antisense Expression of Apple TFL1-like Gene (MdTFL1) Promotes Early Flowering and Causes Phenotypic Changes in Tobacco

Apples (Malus × domestica Borkh.) require up to several years for flowering and bearing fruits. The transition from vegetative to reproductive phase is controlled by floral regulators such as TERMINAL FLOWER 1 (TFL1) and FLOWERING LOCUS T (FT). TFL1 mediates the maintenance of vegetative phase, unlike the antagonistic function of FT to promote the transition into reproductive phase. In this study, we isolated apple TFL1-like gene (MdTFL1) to elucidate various phenotypic traits triggered by the antisense expression of MdTFL1 in tobacco apart from its floral induction function. Early flowering was observed in the tobacco line with MdTFL1 knockout, indicating the reduced time for transition to vegetative phases. Quantitative reverse-transcription PCR showed upregulation of genes involved in the regulation of floral induction, including NtAP1, NtSOC1, NFL1, and NtFTs, and downregulation of carotenoid cleavage dioxygenases (CCDs) and CEN-like genes in transgenic lines. Interestingly, transgenic tobacco expressing antisense MdTFL1 exhibited distinct morphological changes in lateral shoot outgrowth, internode length, and the development of leaves, flowers, and fruits. The results suggested that using the antisense expression of MdTFL1 gene is one of the approaches to shorten the vegetable phase and proposed improvement of plant architecture in horticultural crops.