A MYB-domain protein EFM mediates flowering responses to environmental cues in Arabidopsis

Time-Course Transcriptome Analysis Unveils the CoFKF1-CoMYB4-CoFT1 Regulatory Module in Flowering Control of Camellia oleifera Abel

Camellia oleifera Abel. (C. oleifera) represents a significant woody edible oil species predominantly distributed in southern China. Timely flowering is essential for the growth, development and tea oil production of C. oleifera. However, the mechanisms underpinning this process remain insufficiently understood. In this study, it was demonstrated through time-course transcriptome analysis that we revealed that CoFKF1-like1 (CoFKF1) serves as a central regulatory gene in the flowering process of C. oleifera. The ectopic expression of CoFKF1 resulted in the induction of early flowering. Furthermore, it was observed that CoFKF1 interacts with the transcription factor CoMYB4 in a blue-light-dependent manner, facilitating its ubiquitination and subsequent degradation. Genetically, CoMYB4 was identified as functioning downstream of CoFKF1 by directly binding to the promoter of CoFT1 and repressing its promoter activity. In conclusion, these findings elucidate that CoFKF1 promotes flowering by reducing the stability of the CoMYB4 protein, thereby enhancing CoFT1 promoter activity. Collectively, the results provide critical insights into the flowering mechanisms of C. oleifera and present a promising avenue to optimise its flowering period via the CoFKF1-CoMYB4-CoFT1 module.

Functions and Mechanisms of Histone Modifications in Plants

Histones are far more than just the basic units of chromatin. Posttranslational modifications of histone tails have emerged as important regulatory mechanisms for diverse biological processes, including genome organization, gene expression, transposable element suppression, development, and environmental responses. This field is expanding rapidly with the development of new technologies and growing interest from both the basic and translational research communities. The past two decades have witnessed tremendous progress in our understanding of the complex, multilayered regulation and actions of histone modifications in plants. This review summarizes the characteristics, localization, and molecular functions of histone modifications with an emphasis on the well-studied marks in Arabidopsis. We further discuss their functions in developmental transitions and environmental responses as well as their contributions to epigenomic diversity and plasticity. By highlighting the functions and fundamental mechanisms of epigenetic modifications in model plants, this review underscores the potential to harness epigenetic regulation for agricultural improvement.

A histone demethylase is involved in regulating the transcription factor PSR1 for carbon storage in Chlamydomonas

Histone modifications are widespread in microalgae, a group of photoautotrophs capable of transforming CO2 to diverse bio-products. However, the functional roles of histone modifying enzymes for carbon metabolism remain largely unexplored. Here, we unveiled the involvement of a JmjC domain-containing histone demethylase (CrHDM1), a previously uncharacterized epigenetic regulator, in carbon metabolism by modulating a transcription factor in the model alga Chlamydomonas reinhardtii (thereafter Chlamydomonas). CrHDM1 disruption resulted in increased carbohydrate levels including starch yet attenuated protein and lipid levels in Chlamydomonas, which were restored by genetic complementation with the CrHDM1 gene. Phosphorus Responsive Regulator1 (PSR1), a transcription factor involved in starch storage regulation, was transcriptionally upregulated by CrHDM1 disruption, along with the upregulation of starch synthesis genes. PSR1 knockout in the crhdm1 mutant impaired the CrHDM1 disruption-associated starch increase. CrHDM1, localized in the nucleus, was demonstrated to specifically demethylate H3K4me2 in vitro. Besides, chromatin immunoprecipitation-quantitative PCR experiments showed that the H3K4me2 level at the PSR1 promoter, which positively correlated with PSR1 transcript level, was negatively regulated by CrHDM1. Collectively, our findings uncover a newly discovered epigenetic regulator-transcription factor module involved in starch storage and provide valuable insights into the epigenetic regulation of carbon metabolism in Chlamydomonas.

Antagonizing cis-regulatory elements of a conserved flowering gene mediate developmental robustness

Developmental transitions require precise temporal and spatial control of gene expression. In plants, such regulation is critical for flower formation, which involves the progressive maturation of stem cell populations within shoot meristems to floral meristems, followed by rapid sequential differentiation into floral organs. Across plant taxa, these transitions are orchestrated by the F-box transcriptional cofactor gene UNUSUAL FLORAL ORGANS (UFO). The conserved and pleiotropic functions of UFO offer a useful framework for investigating how evolutionary processes have shaped the intricate cis-regulation of key developmental genes. By pinpointing a conserved promoter sequence in an accessible chromatin region of the tomato ortholog of UFO, we engineered in vivo a series of cis-regulatory alleles that caused both loss- and gain-of-function floral defects. These mutant phenotypes were linked to disruptions in predicted transcription factor binding sites for known transcriptional activators and repressors. Allelic combinations revealed dosage-dependent interactions between opposing alleles, influencing the penetrance and expressivity of gain-of-function phenotypes. These phenotypic differences support that robustness in tomato flower development requires precise temporal control of UFO expression dosage. Bridging our analysis to Arabidopsis, we found that although homologous sequences to the tomato regulatory region are dispersed within the UFO promoter, they maintain similar control over floral development. However, phenotypes from disrupting these sequences differ due to the differing expression patterns of UFO. Our study underscores the complex cis-regulatory control of dynamic developmental genes and demonstrates that critical short stretches of regulatory sequences that recruit both activating and repressing machinery are conserved to maintain developmental robustness.

GhCOL2 Positively Regulates Flowering by Activating the Transcription of GhHD3A in Upland Cotton (Gossypium hirsutum L.)

Plants have evolved sophisticated signaling networks to adjust flowering time, ensuring successful reproduction. Two crucial flowering regulators, FLOWERING LOCUS T (FT) and CONSTANS (CO), play pivotal roles in regulating flowering across various species. Previous studies have indicated that suppressing Gossypium hirsutum CONSTANS-LIKE 2 (GhCOL2), a homolog of Arabidopsis CO, leads to delayed flowering in cultivated cotton. However, the underlying regulatory mechanisms remain unknown. In this study, a yeast one-hybrid and dual-LUC expression assays were used to elucidate the molecular mechanism through which GhCOL2 regulates the transcription of GhHD3A. RT-qPCR was used to examine the expression of GhCOL2 and GhHD3A. Our findings reveal that GhCOL2 directly binds to CCACA cis-elements and atypical CORE (TGTGTATG) cis-elements in the promoter regions of HEADING DATE 3 A (HD3A), thereby activating GhHD3A transcription. Notably, GhCOL2 and GhHD3A exhibited high expression levels in the adult stage and low levels in the juvenile stage. Interestingly, the expression of GhCOL2 and GhHD3A varied significant between the two cotton varieties (Tx2094 and Maxxa). In summary, our study enhances the understanding of the molecular mechanism by which cotton GhCOL2-GhHD3A regulates flowering at the molecular level. Furthermore, it contributes to a broader comprehension of the GhCOL2-GhHD3A model in G. hirsutum.

Down-regulation of the rice HRS1 HOMOLOG3 transcriptional repressor gene due to N deficiency directly co-activates ammonium and phosphate transporter genes

Rice HRS1 HOMOLOG3 (OsHHO3) acts as a transcriptional repressor of AMMONIUM TRANSPORTER1 (OsAMT1) genes in rice; thus, reduced OsHHO3 expression in nitrogen (N)-deficient environments promotes ammonium uptake. In this study, we show that OsHHO3 also functions as a repressor of a specific subset of phosphate (Pi) transporter (PT) genes involved in the uptake and root-to-shoot translocation of Pi, including OsPT2, OsPT4, and OsPHO1;1. Disruption of OsHHO3 increased Pi uptake and Pi contents in shoots and roots, while overexpression of OsHHO3 caused the opposite effects. Furthermore, phosphorus (P) deficiency slightly decreased OsHHO3 expression, up-regulating a specific subset of PT genes. However, N deficiency was more effective than P deficiency in suppressing OsHHO3 expression in roots, and unlike N deficiency-dependent activation of PT genes under the control of OsHHO3, the P deficiency-dependent activation of OsAMT1 genes was minimal. Interestingly, the simultaneous deficiency of both N and P promoted the OsHHO3-regulated expression of PT genes more significantly than the deficiency of either N or P, but diminished the expression of genes regulated by OsPHR2, a master regulator of Pi starvation-responsive transcriptional activation. Phenotypic analysis revealed that the inactivation and overexpression of OsHHO3 improved and reduced plant growth, respectively, under N-deficient and P-deficient conditions. These results indicate that OsHHO3 regulates a specific subset of PT genes independently of OsPHR2-mediated regulation and plays a critical role in the adaptation to diverse N and P environments.

Phosphorylation of the transcription factor SlBIML1 by SlBIN2 kinases delays flowering in tomato

Brassinosteroids (BRs) are well known for their important role in the regulation of plant growth and development. Plants with deficiency in BR signaling show delayed plant development and exhibit late flowering phenotypes. However, the precise mechanisms involved in this process require investigation. In this study, we cloned homologs of BRASSINOSTEROID-INSENSITIVE 2 (SlBIN2), the GSK3-like protein kinase in tomato (Solanum lycopersicum). We characterized growth-related processes and phenotypic changes in the transgenic lines and found that SlBIN2 transgenic lines have delayed development and slow growing phenotypes. SlBIN2s work redundantly to negatively regulate BR signaling in tomato. Furthermore, the transcription factor SlBIN2.1-INTERACTING MYB-LIKE 1 (SlBIML1) was identified as a downstream substrate of SlBIN2s that SlBIN2s interact with and phosphorylate to synergistically regulate tomato developmental processes. Specifically, SlBIN2s modulated protein stability of SlBIML1 by phosphorylating multiple amino acid residues, including the sites Thr266 and Thr280. This study reveals a branch of the BR signaling pathway that regulates the vegetative growth phase and delays floral transition in tomato without the feedback affecting BR signaling. This information enriches our understanding of the downstream transduction pathway of BR signaling and provides potential targets for adjusting tomato flowering time.

Altered expression of a raspberry homologue of VRN1 is associated with disruption of dormancy induction and misregulation of subsets of dormancy-associated genes

Winter dormancy is a key process in the phenology of temperate perennials. Climate change is severely impacting its course leading to economic losses in agriculture. A better understanding of the underlying mechanisms, as well as the genetic basis of the different responses, is necessary for the development of climate-resilient cultivars. This study aims to provide an insight into winter dormancy in red raspberry (Rubus idaeus L). We report the transcriptomic profiles during dormancy in two raspberry cultivars with contrasting responses. The cultivar 'Glen Ample' showed a typical perennial phenology, whereas 'Glen Dee' registered consistent dormancy dysregulation, exhibiting active growth and flowering out of season. RNA-seq combined with weighted gene co-expression network analysis identified gene clusters in both genotypes that exhibited time-dependent expression profiles. Functional analysis of 'Glen Ample' gene clusters highlighted the significance of the cell and structural development prior to dormancy entry as well the role of genetic and epigenetic processes such as RNAi and DNA methylation in regulating gene expression. Dormancy release in 'Glen Ample' was associated with up-regulation of transcripts associated with the resumption of metabolism, nucleic acid biogenesis, and processing signal response pathways. Many of the processes occurring in 'Glen Ample' were dysregulated in 'Glen Dee' and 28 transcripts exhibiting time-dependent expression in 'Glen Ample' that also had an Arabidopsis homologue were not found in 'Glen Dee'. These included a gene with homology to Arabidopsis VRN1 (RiVRN1.1) that exhibited a sharp decline in expression following dormancy induction in 'Glen Ample'. Characterization of the gene region in the 'Glen Dee' genome revealed two large insertions upstream of the ATG start codon. We propose that expression below detection level of a specific VRN1 homologue in 'Glen Dee' causes dormancy misregulation as a result of inappropriate expression of a subset of genes that are directly or indirectly regulated by RiVRN1.1.

Decoding histone 3 lysine methylation: Insights into seed germination and flowering

Histone lysine methylation is a highly conserved epigenetic modification across eukaryotes that contributes to creating different dynamic chromatin states, which may result in transcriptional changes. Over the years, an accumulated set of evidence has shown that histone methylation allows plants to align their development with their surroundings, enabling them to respond and memorize past events due to changes in the environment. In this review, we discuss the molecular mechanisms of histone methylation in plants. Writers, readers, and erasers of Arabidopsis histone methylation marks are described with an emphasis on their role in two of the most important developmental transition phases in plants, seed germination and flowering. Further, the crosstalk between different methylation marks is also discussed. An overview of the mechanisms of histone methylation modifications and their biological outcomes will shed light on existing research gaps and may provide novel perspectives to increase crop yield and resistance in the era of global climate change.

Biological macromolecules mediated by environmental signals affect flowering regulation in plants: A comprehensive review

Flowering time is a crucial developmental stage in the life cycle of plants, as it determines the reproductive success and overall fitness of the organism. The precise regulation of flowering time is influenced by various internal and external factors, including genetic, environmental, and hormonal cues. This review provided a comprehensive overview of the molecular mechanisms and regulatory pathways of biological macromolecules (e.g. proteins and phytohormone) and environmental factors (e.g. light and temperature) involved in the control of flowering time in plants. We discussed the key proteins and signaling pathways that govern the transition from vegetative growth to reproductive development, highlighting the intricate interplay between genetic networks, environmental cues, and phytohormone signaling. Additionally, we explored the impact of flowering time regulation on plant adaptation, crop productivity, and agricultural practices. Moreover, we summarized the similarities and differences of flowering mechanisms between annual and perennial plants. Understanding the mechanisms underlying flowering time control is not only essential for fundamental plant biology research but also holds great potential for crop improvement and sustainable agriculture.

Dynamics of polycomb group marks in Arabidopsis

Polycomb Group (PcG) histone-modifying system is key in maintaining gene repression, providing a mitotically heritable cellular memory. Nevertheless, to allow plants to transition through distinct transcriptional programs during development or to respond to external cues, PcG-mediated repression requires reversibility. Several data suggest that the dynamics of PcG marks may vary considerably in different cell contexts; however, how PcG marks are established, maintained, or removed in each case is far from clear. In this review, we survey the knowns and unknowns of the molecular mechanisms underlying the maintenance or turnover of PcG marks in different cell stages.

Multilayered regulation and implication of flowering time in plants

Initiation of flowering is a key switch for plants to shift from the vegetative growth to the phase of reproductive growth. This critical phase is essential not only for achieving successful reproduction, but also for facilitating environmental adaptation and maximizing yield potential. In the past decades, the environmental factors and genetic pathways that control flowering time have undergone extensive investigation in both model plant Arabidopsis and various crop species. The impact of environmental factors on plant flowering time is well documented. This paper focuses on the multilayered modulation of flowering time. Recent multi-omics approaches, and genetic screens have revealed additional components that modulate flowering time across various levels, encompassing chromatin modification, transcriptional and post-transcriptional control, as well as translational and post-translational regulation. The interplay between these various layers of regulation creates a finely-tuned system that can respond to a wide variety of inputs and allows plants to adjust flowering time in response to changing environmental conditions. In this review, we present a comprehensive overview of the recent progress made in understanding the intricate regulation of flowering time in plants, emphasizing the pivotal molecular components and their intricate interactions. Additionally, we provide an exhaustive list of key genes implicated in the intricate modulation of flowering time and offer a detailed summary of regulators of FLOWERING LOCUS T (FT) and FLOWERING LOCUS (FLC). We also discuss the implications of this knowledge for crop improvement and adaptation to changing environments.

Ribosome Pausing Negatively Regulates Protein Translation in Maize Seedlings during Dark-to-Light Transitions

Regulation of translation is a crucial step in gene expression. Developmental signals and environmental stimuli dynamically regulate translation via upstream small open reading frames (uORFs) and ribosome pausing. Recent studies have revealed many plant genes that are specifically regulated by uORF translation following changes in growth conditions, but ribosome-pausing events are less well understood. In this study, we performed ribosome profiling (Ribo-seq) of etiolated maize (Zea mays) seedlings exposed to light for different durations, revealing hundreds of genes specifically regulated at the translation level during the early period of light exposure. We identified over 400 ribosome-pausing events in the dark that were rapidly released after illumination. These results suggested that ribosome pausing negatively regulates translation from specific genes, a conclusion that was supported by a non-targeted proteomics analysis. Importantly, we identified a conserved nucleotide motif downstream of the pausing sites. Our results elucidate the role of ribosome pausing in the control of gene expression in plants; the identification of the cis-element at the pausing sites provides insight into the mechanisms behind translation regulation and potential targets for artificial control of plant translation.

Role of GARP family transcription factors in the regulatory network for nitrogen and phosphorus acquisition

The GARP (Golden2, ARR-B, Psr1) family proteins with a conserved DNA-binding domain, called the B-motif, are plant-specific transcription factors involved in the regulation of various physiological processes. The GARP family proteins are divided into members that function as monomeric transcription factors, and members that function as transcription factors in the dimeric form, owing to the presence of a coiled-coil dimerization domain. Recent studies revealed that the dimer-forming GARP family members, which are further divided into the PHR1 and NIGT1 subfamilies, play critical roles in the regulation of phosphorus (P) and nitrogen (N) acquisition. In this review, we present a general overview of the GARP family proteins and discuss how several members of the PHR1 and NIGT1 subfamilies are involved in the coordinated acquisition of P and N in response to changes in environmental nutrient conditions, while mainly focusing on the recent findings that enhance our knowledge of the roles of PHR1 and NIGT1 in phosphate starvation signaling and nitrate signaling.

The GARP family transcription factor MtHHO3 negatively regulates salt tolerance in Medicago truncatula

High salinity is one of the detrimental environmental factors restricting plant growth and crop production throughout the world. This study demonstrated that the GARP family transcription factor MtHHO3 is involved in response to salt stress and abscisic acid (ABA) signaling in Medicago truncatula. The transcription of MtHHO3 was repressed by salt, osmotic stress, and ABA treatment. The seed germination assay showed that, overexpression of MtHHO3 in Arabidopsis thaliana caused hypersensitivity to salt and osmotic stress, but increased resistance to ABA inhibition. Overexpression of MtHHO3 in M. truncatula resulted in decreased tolerance of salinity, while loss-of-function mutants mthho3-1 and mthho3-2 were more resistant to salt stress compared with wild-type plants. qRT-PCR analyses showed that MtHHO3 downregulated the expression of genes in stress and ABA responsive pathways. We further demonstrated that MtHHO3 repressed the transcription of the pathogenesis-related gene MtPR2 by binding to its promoter. Overall, these results indicate that MtHHO3 negatively regulates salt stress response in plants and deepen our understanding of the role of the GARP subfamily transcription factors in modulating salt stress and ABA signaling.

Beyond heat waves: Unlocking epigenetic heat stress memory in Arabidopsis

Plants remember their exposure to environmental changes and respond more effectively the next time they encounter a similar change by flexibly altering gene expression. Epigenetic mechanisms play a crucial role in establishing such memory of environmental changes and fine-tuning gene expression. With the recent advancements in biochemistry and sequencing technologies, it has become possible to characterize the dynamics of epigenetic changes on scales ranging from short term (minutes) to long term (generations). Here, our main focus is on describing the current understanding of the temporal regulation of histone modifications and chromatin changes during exposure to short-term recurring high temperatures and reevaluating them in the context of natural environments. Investigations of the dynamics of histone modifications and chromatin structural changes in Arabidopsis after repeated exposure to heat at short intervals have revealed the detailed molecular mechanisms of short-term heat stress memory, which include histone modification enzymes, chromatin remodelers, and key transcription factors. In addition, we summarize the spatial regulation of heat responses. Based on the natural temperature patterns during summer, we discuss how plants cope with recurring heat stress occurring at various time intervals by utilizing 2 distinct types of heat stress memory mechanisms. We also explore future research directions to provide a more precise understanding of the epigenetic regulation of heat stress memory.

A dephosphorylation-dependent molecular switch for FT repression mediates flowering in Arabidopsis

The reproductive success of flowering plants relies greatly on precise timing of the floral transition, which is finely modulated by a complex network of floral regulators. As a main floral integrator, FLOWERING LOCUS T (FT) is also an essential constituent of the florigen that is transported from leaves to shoot apices to induce flowering. FT is specifically transcribed in leaf vascular tissues, where its production is suppressed by many flowering repressors, including the MYB transcription factor EARLY FLOWERING MYB PROTEIN (EFM). Here, we show that a plant CTD phosphatase, C-TERMINAL DOMAIN PHOSPHATASE-LIKE 2 (CPL2), suppresses FT expression in leaf vascular tissues by modulating the binding activity of EFM. CPL2 interacts with and dephosphorylates EFM to facilitate the binding of dephosphorylated EFM to FT chromatin, thereby inhibiting flowering. Our results suggest that CPL2-mediated dephosphorylation of the floral repressor EFM serves as a molecular switch, adding another layer of regulation to fine-tune FT transcription and ensure that flowering occurs at an appropriate time.

Genome-wide association study reveals GmFulb as candidate gene for maturity time and reproductive length in soybeans (Glycine max)

The ability of soybean [Glycine max (L.) Merr.] to adapt to different latitudes is attributed to genetic variation in major E genes and quantitative trait loci (QTLs) determining flowering time (R1), maturity (R8), and reproductive length (RL). Fully revealing the genetic basis of R1, R8, and RL in soybeans is necessary to enhance genetic gains in soybean yield improvement. Here, we performed a genome-wide association analysis (GWA) with 31,689 single nucleotide polymorphisms (SNPs) to detect novel loci for R1, R8, and RL using a soybean panel of 329 accessions with the same genotype for three major E genes (e1-as/E2/E3). The studied accessions were grown in nine environments and observed for R1, R8 and RL in all environments. This study identified two stable peaks on Chr 4, simultaneously controlling R8 and RL. In addition, we identified a third peak on Chr 10 controlling R1. Association peaks overlap with previously reported QTLs for R1, R8, and RL. Considering the alternative alleles, significant SNPs caused RL to be two days shorter, R1 two days later and R8 two days earlier, respectively. We identified association peaks acting independently over R1 and R8, suggesting that trait-specific minor effect loci are also involved in controlling R1 and R8. From the 111 genes highly associated with the three peaks detected in this study, we selected six candidate genes as the most likely cause of R1, R8, and RL variation. High correspondence was observed between a modifying variant SNP at position 04:39294836 in GmFulb and an association peak on Chr 4. Further studies using map-based cloning and fine mapping are necessary to elucidate the role of the candidates we identified for soybean maturity and adaptation to different latitudes and to be effectively used in the marker-assisted breeding of cultivars with optimal yield-related traits.

MED8 regulates floral transition in Arabidopsis by interacting with FPA

Success in plant reproduction is highly dependent on the correct timing of the floral transition, which is tightly regulated by the flowering pathways. In the model plant Arabidopsis thaliana, the central flowering repressor FLOWERING LOCUS C (FLC) is precisely regulated by multiple flowering time regulators in the vernalization pathway and autonomous pathway, including FPA. Here we report that Arabidopsis MEDIATOR SUBUNIT 8 (MED8) promotes floral transition in Arabidopsis by recruiting FPA to the FLC locus to repress FLC expression. Loss of MED8 function leads to a significant late-flowering phenotype due to increased FLC expression. We further show that MED8 directly interacts with FPA in the nucleus and recruits FPA to the FLC locus. Moreover, MED8 is indispensable for FPA's function in controlling flowering time and regulating FLC expression. Our study thus reveals a flowering mechanism by which the Mediator subunit MED8 represses FLC expression by facilitating the binding of FPA to the FLC locus to ensure appropriate timing of flowering for reproductive success.

An overview of floral regulatory genes in annual and perennial plants

The floral initiation in angiosperms is a complex process influenced by endogenous and exogenous signals. With this approach, we aim to provide a comprehensive review to integrate this complex floral regulatory process and summarize the regulatory genes and their functions in annuals and perennials. Seven primary paths leading to flowering have been discovered in Arabidopsis under several growth condition that include; photoperiod, ambient temperature, vernalization, gibberellins, autonomous, aging and carbohydrates. These pathways involve a series of interlinked signaling pathways that respond to both internal and external signals, such as light, temperature, hormones, and developmental cues, to coordinate the expression of genes that are involved in flower development. Among them, the photoperiodic pathway was the most important and conserved as some of the fundamental loci and mechanisms are shared even by closely related plant species. The activation of floral regulatory genes such as FLC, FT, LFY, and SOC1 that determine floral meristem identity and the transition to the flowering stage result from the merging of these pathways. Recent studies confirmed that alternative splicing, antisense RNA and epigenetic modification play crucial roles by regulating the expression of genes related to blooming. In this review, we documented recent progress in the floral transition time in annuals and perennials, with emphasis on the specific regulatory mechanisms along with the application of various molecular approaches including overexpression studies, RNA interference and Virus-induced flowering. Furthermore, the similarities and differences between annual and perennial flowering will aid significant contributions to the field by elucidating the mechanisms of perennial plant development and floral initiation regulation.

Genome-wide association study for temperature response and photo-thermal interaction of flowering time in soybean using a panel of cultivars with diverse maturity groups

KEY MESSAGE

A total of 101 QTNs were found to be associated with soybean flowering time responses to photo-thermal conditions; three candidate genes with non-synonymous substitutions were identified: Glyma.08G302500 (GmHY5), Glyma.08G303900 (GmPIF4c), and Glyma.16G046700 (GmVRN1). The flowering transition is a crucial component of soybean (Glycine max L. Merr.) development. The transition process is regulated by photoperiod, temperature, and their interaction. To examine the genetic architecture associated with temperature- and photo-thermal-mediated regulation of soybean flowering, we here performed a genome-wide association study using a panel of 201 soybean cultivars with maturity groups ranging from MG 000 to VIII. Each cultivar was grown in artificially controlled photoperiod and different seasons in 2017 and 2018 to assess the thermal response (TR) and the interactive photo-thermal response (IPT) of soybean flowering time. The panel contained 96,299 SNPs with minor allele frequencies > 5%; 33, 19, and 49 of these SNPs were significantly associated with only TR, only IPT, and both TR and IPT, respectively. Twenty-one SNPs were located in or near previously reported quantitative trait loci for first-flowering; 16 SNPs were located within 200 kb of the main-effect flowering genes GmFT2a, GmFT2b, GmFT3a, GmFT3b, GmFT5a, GmFT5b, GmCOL2b, GmPIF4b, and GmPIF4c, or near homologs of the known Arabidopsis thaliana flowering genes BBX19, VRN1, TFL1, FUL, AGL19, SPA1, HY5, PFT1, and EDF1. Natural non-synonymous allelic variations were identified in the candidate genes Glyma.08G302500 (GmHY5), Glyma.08G303900 (GmPIF4c), and Glyma.16G046700 (GmVRN1). Cultivars with different haplotypes showed significant variations in TR, IPT, and flowering time in multiple environments. The favorable alleles, candidate genes, and diagnostic SNP markers identified here provide valuable information for future improvement of soybean photo-thermal adaptability, enabling expansion of soybean production regions and improving plant resilience to global climate change.

Control of histone demethylation by nuclear-localized α-ketoglutarate dehydrogenase

Methylations on nucleosomal histones play fundamental roles in regulating eukaryotic transcription. Jumonji C domain-containing histone demethylases (JMJs) dynamically control the level of histone methylations. However, how JMJ activity is generally regulated is unknown. We found that the tricarboxylic acid cycle-associated enzyme α-ketoglutarate (α-KG) dehydrogenase (KGDH) entered the nucleus, where it interacted with various JMJs to regulate α-KG-dependent histone demethylations by JMJs, and thus controlled genome-wide gene expression in plants. We show that nuclear targeting is regulated by environmental signals and that KGDH is enriched at thousands of loci in Arabidopsis thaliana. Chromatin-bound KGDH catalyzes α-KG decarboxylation and thus may limit its local availability to KGDH-coupled JMJs, inhibiting histone demethylation. Thus, our results uncover a regulatory mechanism for histone demethylations by JMJs.

Photoperiodic flowering in Arabidopsis: Multilayered regulatory mechanisms of CONSTANS and the florigen FLOWERING LOCUS T

The timing of flowering affects the success of sexual reproduction. This developmental event also determines crop yield, biomass, and longevity. Therefore, this mechanism has been targeted for improvement along with crop domestication. The underlying mechanisms of flowering are highly conserved in angiosperms. Central to these mechanisms is how environmental and endogenous conditions control transcriptional regulation of the FLOWERING LOCUS T (FT) gene, which initiates floral development under long-day conditions in Arabidopsis. Since the identification of FT as florigen, efforts have been made to understand the regulatory mechanisms of FT expression. Although many transcriptional regulators have been shown to directly influence FT, the question of how they coordinately control the spatiotemporal expression patterns of FT still requires further investigation. Among FT regulators, CONSTANS (CO) is the primary one whose protein stability is tightly controlled by phosphorylation and ubiquitination/proteasome-mediated mechanisms. In addition, various CO interaction partners, some of them previously identified as FT transcriptional regulators, positively or negatively modulate CO protein activity. The FT promoter possesses several transcriptional regulatory "blocks," highly conserved regions among Brassicaceae plants. Different transcription factors bind to specific blocks and affect FT expression, often causing topological changes in FT chromatin structure, such as the formation of DNA loops. We discuss the current understanding of the regulation of FT expression mainly in Arabidopsis and propose future directions related to this topic.

Predicting yield of individual field-grown rapeseed plants from rosette-stage leaf gene expression

In the plant sciences, results of laboratory studies often do not translate well to the field. To help close this lab-field gap, we developed a strategy for studying the wiring of plant traits directly in the field, based on molecular profiling and phenotyping of individual plants. Here, we use this single-plant omics strategy on winter-type Brassica napus (rapeseed). We investigate to what extent early and late phenotypes of field-grown rapeseed plants can be predicted from their autumnal leaf gene expression, and find that autumnal leaf gene expression not only has substantial predictive power for autumnal leaf phenotypes but also for final yield phenotypes in spring. Many of the top predictor genes are linked to developmental processes known to occur in autumn in winter-type B. napus accessions, such as the juvenile-to-adult and vegetative-to-reproductive phase transitions, indicating that the yield potential of winter-type B. napus is influenced by autumnal development. Our results show that single-plant omics can be used to identify genes and processes influencing crop yield in the field.

Multiple transcriptome comparisons reveal the essential roles of FLOWERING LOCUS T in floral initiation and SOC1 and SVP in floral activation in blueberry

The flowering mechanisms, especially chilling requirement-regulated flowering, in deciduous woody crops remain to be elucidated. Flower buds of northern highbush blueberry cultivar Aurora require approximately 1,000 chilling hours to bloom. Overexpression of a blueberry FLOWERING LOCUS T (VcFT) enabled precocious flowering of transgenic “Aurora” mainly in non-terminated apical buds during flower bud formation, meanwhile, most of the mature flower buds could not break until they received enough chilling hours. In this study, we highlighted two groups of differentially expressed genes (DEGs) in flower buds caused by VcFT overexpression (VcFT-OX) and full chilling. We compared the two groups of DEGs with a focus on flowering pathway genes. We found: 1) In non-chilled flower buds, VcFT-OX drove a high VcFT expression and repressed expression of a major MADS-box gene, blueberry SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (VcSOC1) resulting an increased VcFT/VcSOC1 expression ratio; 2) In fully chilled flower buds that are ready to break, the chilling upregulated VcSOC1 expression in non-transgenic “Aurora” and repressed VcFT expression in VcFT-OX “Aurora”, and each resulted in a decreased ratio of VcFT to VcSOC1; additionally, expression of a blueberry SHORT VEGETATIVE PHASE (VcSVP) was upregulated in chilled flower buds of both transgenic and non-transgenic’ “Aurora”. Together with additional analysis of VcFT and VcSOC1 in the transcriptome data of other genotypes and tissues, we provide evidence to support that VcFT expression plays a significant role in promoting floral initiation and that VcSOC1 expression is a key floral activator. We thus propose a new hypothesis on blueberry flowering mechanism, of which the ratios of VcFT-to-VcSOC1 at transcript levels in the flowering pathways determine flower bud formation and bud breaking. Generally, an increased VcFT/VcSOC1 ratio or increased VcSOC1 in leaf promotes precocious flowering and flower bud formation, and a decreased VcFT/VcSOC1 ratio with increased VcSOC1 in fully chilled flower buds contributes to flower bud breaking.

Genome-Scale Investigation of GARP Family Genes Reveals Their Pivotal Roles in Nutrient Stress Resistance in Allotetraploid Rapeseed

The GARP genes are plant-specific transcription factors (TFs) and play key roles in regulating plant development and abiotic stress resistance. However, few systematic analyses of GARPs have been reported in allotetraploid rapeseed (Brassica napus L.) yet. In the present study, a total of 146 BnaGARP members were identified from the rapeseed genome based on the sequence signature. The BnaGARP TFs were divided into five subfamilies: ARR, GLK, NIGT1/HRS1/HHO, KAN, and PHL subfamilies, and the members within the same subfamilies shared similar exon-intron structures and conserved motif configuration. Analyses of the Ka/Ks ratios indicated that the GARP family principally underwent purifying selection. Several cis-acting regulatory elements, essential for plant growth and diverse biotic and abiotic stresses, were identified in the promoter regions of BnaGARPs. Further, 29 putative miRNAs were identified to be targeting BnaGARPs. Differential expression of BnaGARPs under low nitrate, ammonium toxicity, limited phosphate, deficient boron, salt stress, and cadmium toxicity conditions indicated their potential involvement in diverse nutrient stress responses. Notably, BnaA9.HHO1 and BnaA1.HHO5 were simultaneously transcriptionally responsive to these nutrient stresses in both hoots and roots, which indicated that BnaA9.HHO1 and BnaA1.HHO5 might play a core role in regulating rapeseed resistance to nutrient stresses. Therefore, this study would enrich our understanding of molecular characteristics of the rapeseed GARPs and will provide valuable candidate genes for further in-depth study of the GARP-mediated nutrient stress resistance in rapeseed.

Single-nuclei transcriptome analysis of the shoot apex vascular system differentiation in Populus

Differentiation of stem cells in the plant apex gives rise to aerial tissues and organs. Presently, we lack a lineage map of the shoot apex cells in woody perennials - a crucial gap considering their role in determining primary and secondary growth. Here, we used single-nuclei RNA-sequencing to determine cell type-specific transcriptomes of the Populus vegetative shoot apex. We identified highly heterogeneous cell populations clustered into seven broad groups represented by 18 transcriptionally distinct cell clusters. Next, we established the developmental trajectories of the epidermis, leaf mesophyll and vascular tissue. Motivated by the high similarities between Populus and Arabidopsis cell population in the vegetative apex, we applied a pipeline for interspecific single-cell gene expression data integration. We contrasted the developmental trajectories of primary phloem and xylem formation in both species, establishing the first comparison of vascular development between a model annual herbaceous and a woody perennial plant species. Our results offer a valuable resource for investigating the principles underlying cell division and differentiation conserved between herbaceous and perennial species while also allowing us to examine species-specific differences at single-cell resolution.

RETRACTED: Genome-wide analysis of the B-box gene family in the sweetpotato wild ancestor Ipomoea trifida and determination of the function of IbBBX28 in the regulation of flowering time of Arabidopsis

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of of the Editors-in-Chief. A large part of the article is highly similar to the paper previously published by Wenqian Hou, Lei Ren, Yang Zhang, Haoyun Sun, Tianye Shi, Yulan Gu, Aimin Wang, Daifu Ma, Zongyun Li and Lei Zhang in Scientia Horticulturae 288 (2021) 110374 https://doi.org/10.1016/j.scienta.2021.110374. In particular, a large part of the two articles shows a study on the same gene family in the same plant, with similar methodological approaches, resulting in a series of highly similar figures. One of the conditions of submission of a paper for publication is that authors declare explicitly that their work is original and has not appeared in a publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

Genome-wide identification and expression analysis of JmjC domain-containing genes in grape under MTA treatment

Histone demethylases containing the JmjC domain play an extremely important role in maintaining the homeostasis of histone methylation and are closely related to plant growth and development. Currently, the JmjC domain-containing proteins have been reported in many species; however, they have not been systematically studied in grapes. In this paper, 21 VviJMJ gene family members were identified from the whole grape genome, and the VviJMJ genes were classified into five subfamilies: KDM3, KDM4, KDM5, JMJD6, and JMJ-only based on the phylogenetic relationship and structural features of Arabidopsis and grape. After that, the conserved sites of VviJMJ genes were revealed by protein sequence analysis. In addition, chromosomal localization and gene structure analysis revealed the heterogeneous distribution of VviJMJ genes on grape chromosomes and the structural features of VviJMJ genes, respectively. Analysis of promoter cis-acting elements demonstrated numerous hormone, light, and stress response elements in the promoter region of the VviJMJ genes. Subsequently, the grape fruit was treated with MTA (an H3K4 methylation inhibitor), which significantly resulted in the early ripening of grape fruits. The qRT-PCR analysis showed that VviJMJ genes (except VviJMJ13c) had different expression patterns during grape fruit development. The expression of VviJMJ genes in the treatment group was significantly higher than that in the control group. The results indicate that VviJMJ genes are closely related to grape fruit ripening.

2b-RAD Genotyping of the Seagrass Cymodocea nodosa Along a Latitudinal Cline Identifies Candidate Genes for Environmental Adaptation

Plant populations distributed along broad latitudinal gradients often show patterns of clinal variation in genotype and phenotype. Differences in photoperiod and temperature cues across latitudes influence major phenological events, such as timing of flowering or seed dormancy. Here, we used an array of 4,941 SNPs derived from 2b-RAD genotyping to characterize population differentiation and levels of genetic and genotypic diversity of three populations of the seagrass Cymodocea nodosa along a latitudinal gradient extending across the Atlantic-Mediterranean boundary (i.e., Gran Canaria—Canary Islands, Faro—Portugal, and Ebro Delta—Spain). Our main goal was to search for potential outlier loci that could underlie adaptive differentiation of populations across the latitudinal distribution of the species. We hypothesized that such polymorphisms could be related to variation in photoperiod-temperature regime occurring across latitudes. The three populations were clearly differentiated and exhibited diverse levels of clonality and genetic diversity. Cymodocea nodosa from the Mediterranean displayed the highest genotypic richness, while the Portuguese population had the highest clonality values. Gran Canaria exhibited the lowest genetic diversity (as observed heterozygosity). Nine SNPs were reliably identified as outliers across the three sites by two different methods (i.e., BayeScan and pcadapt), and three SNPs could be associated to specific protein-coding genes by screening available C. nodosa transcriptomes. Two SNPs-carrying contigs encoded for transcription factors, while the other one encoded for an enzyme specifically involved in the regulation of flowering time, namely Lysine-specific histone demethylase 1 homolog 2. When analyzing biological processes enriched within the whole dataset of outlier SNPs identified by at least one method, “regulation of transcription” and “signalling” were among the most represented. Our results highlight the fundamental importance signal integration and gene-regulatory networks, as well as epigenetic regulation via DNA (de)methylation, could have for enabling adaptation of seagrass populations along environmental gradients.

Structure and mechanism of histone methylation dynamics in Arabidopsis

Histone methylation plays a central role in regulating chromatin state and gene expression in Arabidopsis and is involved in a variety of physiological and developmental processes. Dynamic regulation of histone methylation relies on both histone methyltransferase "writer" and histone demethylases "eraser" proteins. In this review, we focus on the four major histone methylation modifications in Arabidopsis H3, H3K4, H3K9, H3K27, and H3K36, and summarize current knowledge of the dynamic regulation of these modifications, with an emphasis on the biochemical and structural perspectives of histone methyltransferases and demethylases.

Impact of Heat Stress on Expression of Wheat Genes Responsive to Hessian Fly Infestation

Heat stress compromises wheat (Triticum aestivium) resistance to Hessian fly (HF, Mayetiola destructor (Say)). This study aimed to investigate the impact of heat stress on transcript expression of wheat genes associated with resistance to HF infestation under normal and heat-stressed conditions. To this end, ‘Molly’, a wheat cultivar containing the resistance gene H13, was subjected to HF infestation, heat stress, and the combination of HF infestation and heat stress. Our RNA-Seq approach identified 21 wheat genes regulated by HF infestation under normal temperatures (18 °C) and 155 genes regulated by HF infestation when plants were exposed to 35 °C for 6 h. Three differentially expressed genes (DEGs) from the RNA-Seq analysis were selected to validate the gene function of these DEGs using the RT-qPCR approach, indicating that these DEGs may differentially contribute to the expression of wheat resistance during the early stage of wheat–HF interaction under various stresses. Moreover, the jasmonate ZIM domain (JAZ) gene was also significantly upregulated under these treatments. Our results suggest that the genes in heat-stressed wheat plants are more responsive to HF infestation than those in plants growing under normal temperature conditions, and these genes in HF-infested wheat plants are more responsive to heat stress than those in plants without infestation.

Overexpression of histone demethylase gene SlJMJ524 from tomato confers Cd tolerance by regulating metal transport-related protein genes and flavonoid content in Arabidopsis

Cadmium (Cd), as a heavy metal, not only negatively affects the development and yield of plants, but also threatens human health due to its accumulation in plants. Increasing evidences indicate that the JUMONJI-C DOMAIN-CONTAINING PROTEIN (JMJ) gene family plays a key role in regulating plant development and stress. Therefore, in this study, SlJMJ524, a 1254 bp gene encoding the jumonji C domain (417 amino acids), was highly expressed in tomato leaves and flowers. Interestingly, the transgenic plants exhibited sensitivity to Cd during post-germination stage but showed enhanced tolerance to the heavy metal during adult stage. Overexpression of SlJMJ524 increased the expression level of related proteins gene involved in heavy metal uptake while increasing Cd tolerance through the GSH-PC pathway. The higher transcription of genes related to flavonoid synthesis reflected higher accumulations of flavonoids in transgenic plants. Our study demonstrated that the ectopic expression of SlJMJ524 conferred the transgenic plants many traits for improving cadmium stress tolerance at different developmental stages. This study advances our collective understanding of the functional role of JMJs and can be used to improve the cadmium tolerance and breeding of crops and plants.

Genome-wide Identification and Expression Analysis of RcMYB Genes in Rhodiola crenulata

Modern research has proved that the main medicinal component of Rhodiola crenulata, which has a wide range of medicinal value, is its secondary metabolite salidroside. The MYB transcription factor family is widely involved in biosynthesis of second metabolism and other roles in the stress response in plants, so a genome-wide identification and analysis for this family in R. crenulata is worth conducting. In this research, genome-wide analysis identified 139 MYB genes based on conserved domains in the R. crenulata genome, and 137 genes were used to construct a phylogenetic tree and modified with expression files to reveal evolutionary characteristics. Physical and chemical characteristics, gene structure, and conserved motif analysis were also used to further analyze RcMYBs. Additionally, cis-acting elements related to transcription, hormone, and MYB binding were found in the promoter region of the selected RcMYBs. Four RcMYBs were cloned, sequenced, and their gene expression pattern was analyzed for further analysis of their functions. The research results lay the foundation for further research on the function of RcMYB and R. crenulata.

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.

SlJMJ7 orchestrates tomato fruit ripening via crosstalk between H3K4me3 and DML2-mediated DNA demethylation

The ripening of fleshy fruits is a unique developmental process that Arabidopsis and rice lack. This process is driven by hormones and transcription factors. However, the critical and early regulators of fruit ripening are still poorly understood. Here, we revealed that SlJMJ7, an H3K4 demethylase, is a critical negative regulator of fruit ripening in tomato. Combined genome-wide transcription, binding sites, histone H3K4me3 and DNA methylation analyses demonstrated that SlJMJ7 regulates a key group of ripening-related genes, including ethylene biosynthesis (ACS2, ACS4 and ACO6), transcriptional regulation (RIN and NOR) and DNA demethylation (DML2) genes, by H3K4me3 demethylation. Moreover, loss of SlJMJ7 function leads to increased H3K4me3 levels, which directly activates ripening-related genes, and to global DML2-mediated DNA hypomethylation in fruit, which indirectly prompts expression of ripening-related genes. Together, these effects lead to accelerated fruit ripening in sljmj7 mutant. Our findings demonstrate that SlJMJ7 acts as a master negative regulator of fruit ripening not only through direct removal of H3K4me3 from multiple key ripening-related factors, but also through crosstalk between histone and DNA demethylation. These findings reveal a novel crosstalk between histone methylation and DNA methylation to regulate gene expression in plant developmental processes.

Identification of Flowering Regulatory Networks and Hub Genes Expressed in the Leaves of Elymus sibiricus L. Using Comparative Transcriptome Analysis

Flowering is a significant stage from vegetative growth to reproductive growth in higher plants, which impacts the biomass and seed yield. To reveal the flowering time variations and identify the flowering regulatory networks and hub genes in Elymus sibiricus, we measured the booting, heading, and flowering times of 66 E. sibiricus accessions. The booting, heading, and flowering times varied from 136 to 188, 142 to 194, and 148 to 201 days, respectively. The difference in flowering time between the earliest- and the last-flowering accessions was 53 days. Furthermore, transcriptome analyses were performed at the three developmental stages of six accessions with contrasting flowering times. A total of 3,526 differentially expressed genes (DEGs) were predicted and 72 candidate genes were identified, including transcription factors, known flowering genes, and plant hormone-related genes. Among them, four candidate genes (LATE, GA2OX6, FAR3, and MFT1) were significantly upregulated in late-flowering accessions. LIMYB, PEX19, GWD3, BOR7, PMEI28, LRR, and AIRP2 were identified as hub genes in the turquoise and blue modules which were related to the development time of flowering by weighted gene co-expression network analysis (WGCNA). A single-nucleotide polymorphism (SNP) of LIMYB found by multiple sequence alignment may cause late flowering. The expression pattern of flowering candidate genes was verified in eight flowering promoters (CRY, COL, FPF1, Hd3, GID1, FLK, VIN3, and FPA) and four flowering suppressors (CCA1, ELF3, Ghd7, and COL4) under drought and salt stress by qRT-PCR. The results suggested that drought and salt stress activated the flowering regulation pathways to some extent. The findings of the present study lay a foundation for the functional verification of flowering genes and breeding of new varieties of early- and late-flowering E. sibiricus.

QTL and candidate gene identification of the node of the first fruiting branch (NFFB) by QTL-seq in upland cotton (Gossypium hirsutum L.)

Background

The node of the first fruiting branch (NFFB) is an important precocious trait in cotton. Many studies have been conducted on the localization of quantitative trait loci (QTLs) and genes related to fiber quality and yield, but there has been little attention to traits related to early maturity, especially the NFFB, in cotton.

Results

To identify the QTL associated with the NFFB in cotton, a BC₄F₂ population comprising 278 individual plants was constructed. The parents and two DNA bulks for high and low NFFB were whole genome sequenced, and 243.8 Gb of clean nucleotide data were generated. A total of 449,302 polymorphic SNPs and 135,353 Indels between two bulks were identified for QTL-seq. Seventeen QTLs were detected and localized on 11 chromosomes in the cotton genome, among which two QTLs (qNFFB-Dt2–1 and qNFFB-Dt3–3) were located in hotspots. Two candidate genes (GhAPL and GhHDA5) related to the NFFB were identified using quantitative real-time PCR (qRT-PCR) and virus-induced gene silencing (VIGS) experiments in this study. Both genes exhibited higher expression levels in the early-maturing cotton material RIL182 during flower bud differentiation, and the silencing of GhAPL and GhHDA5 delayed the flowering time and increased the NFFB compared to those of VA plants in cotton.

Conclusions

Our study preliminarily found that GhAPL and GhHDA5 are related to the early maturity in cotton. The findings provide a basis for the further functional verification of candidate genes related to the NFFB and contribute to the study of early maturity in cotton.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08164-2.

Reprogramming of Histone H3 Lysine Methylation During Plant Sexual Reproduction

Plants undergo extensive reprogramming of chromatin status during sexual reproduction, a process vital to cell specification and pluri- or totipotency establishment. As a crucial way to regulate chromatin organization and transcriptional activity, histone modification can be reprogrammed during sporogenesis, gametogenesis, and embryogenesis in flowering plants. In this review, we first introduce enzymes required for writing, recognizing, and removing methylation marks on lysine residues in histone H3 tails, and describe their differential expression patterns in reproductive tissues, then we summarize their functions in the reprogramming of H3 lysine methylation and the corresponding chromatin re-organization during sexual reproduction in Arabidopsis, and finally we discuss the molecular significance of histone reprogramming in maintaining the pluri- or totipotency of gametes and the zygote, and in establishing novel cell fates throughout the plant life cycle. Despite rapid achievements in understanding the molecular mechanism and function of the reprogramming of chromatin status in plant development, the research in this area still remains a challenge. Technological breakthroughs in cell-specific epigenomic profiling in the future will ultimately provide a solution for this challenge.

Genetic divergence and local adaptation of Liriodendron driven by heterogeneous environments

Ecological adaptive differentiation alters both the species diversity and intraspecific genetic diversity in forests, thus affecting the stability of forest ecosystems. Therefore, knowledge of the genetic underpinnings of the ecological adaptive differentiation of forest species is critical for effective species conservation. In this study, single-nucleotide polymorphisms (SNPs) from population transcriptomes were used to investigate the spatial distribution of genetic variation in Liriodendron to assess whether environmental variables can explain genetic divergence. We examined the contributions of environmental variables to population divergence and explored the genetic underpinnings of local adaptation using a landscape genomic approach. Niche models and statistical analyses showed significant niche divergence between L. chinense and L. tulipifera, suggesting that ecological adaptation may play a crucial role in driving interspecific divergence. We detected a new fine-scale genetic structure in L. chinense, and divergence of the six groups occurred during the late Pliocene to early Pleistocene. Redundancy analysis (RDA) revealed significant associations between genetic variation and multiple environmental variables. Environmental association analyses identified 67 environmental association loci (EALs; nonsynonymous SNPs) that underwent interspecific or intraspecific differentiation, 28 of which were associated with adaptive genes. These 28 candidate adaptive loci provide substantial evidence for local adaptation in Liriodendron. Our findings reveal ecological adaptive divergence pattern between Liriodendron species and provide novel insight into the role of heterogeneous environments in shaping genetic structure and driving local adaptation among populations, informing future L. chinense conservation efforts.

A teosinte-derived allele of a MYB transcription repressor confers multiple disease resistance in maize

Natural alleles that control multiple disease resistance (MDR) are valuable for crop breeding. However, only one MDR gene has been cloned in maize, and the molecular mechanisms of MDR remain unclear in maize. In this study, through map-based cloning we cloned a teosinte-derived allele of a resistance gene, Mexicana lesion mimic 1 (ZmMM1), which causes a lesion mimic phenotype and confers resistance to northern leaf blight (NLB), gray leaf spot (GLS), and southern corn rust (SCR) in maize. Strong MDR conferred by the teosinte allele is linked with polymorphisms in the 3' untranslated region of ZmMM1 that cause increased accumulation of ZmMM1 protein. ZmMM1 acts as a transcription repressor and negatively regulates the transcription of specific target genes, including ZmMM1-target gene 3 (ZmMT3), which functions as a negative regulator of plant immunity and associated cell death. The successful isolation of the ZmMM1 resistance gene will help not only in developing broad-spectrum and durable disease resistance but also in understanding the molecular mechanisms underlying MDR.

Plant NIGT1/HRS1/HHO Transcription Factors: Key Regulators with Multiple Roles in Plant Growth, Development, and Stress Responses

The NIGT1/HRS1/HHO transcription factor (TF) family is a new subfamily of the G2-like TF family in the GARP superfamily and contains two conserved domains: the Myb-DNA binding domain and the hydrophobic and globular domain. Some studies showed that NIGT1/HRS1/HHO TFs are involved in coordinating the absorption and utilization of nitrogen and phosphorus. NIGT1/HRS1/HHO TFs also play an important role in plant growth and development and in the responses to abiotic stresses. This review focuses on recent advances in the structural characteristics of the NIGT1/HRS1/HHO TF family and discusses how the roles and functions of the NIGT1/HRS1/HHO TFs operate in terms of in plant growth, development, and stress responses.

Iron deficiency-induced transcription factors bHLH38/100/101 negatively modulate flowering time in Arabidopsis thaliana

The mechanisms regulating flowering have been extensively studied and the roles of many environmental signals in this process have been reported. However, little is known on the relationship between iron deficiency and flowering regulation, although the response mechanism to iron deficiency has been studied for decades. In this study, we observed that the flowering time of wild-type Arabidopsis thaliana was significantly repressed by iron deficiency under long days. Phenotype analysis showed that iron deficiency delayed flowering of Arabidopsis through the iron deficiency-induced transcription factors bHLH38, bHLH100, and bHLH101 (bHLH38/100/101), which redundantly regulated flowering time and expression of FLOWERING LOCUS T (FT) specifically under long days. Genetic analysis indicated that disruption of FT expression suppressed the early-flowering phenotype of bhlh38/100/101 triple-mutant plants, indicating that bHLH38/100/101 are dependent on functional FT. Furthermore, bHLH38/100/101 interacted with CONSTANS (CO), thereby interfering with the transcriptional activation of CO to regulate FT expression. Therefore, the results indicated that iron deficiency affects flowering of Arabidopsis under long days through bHLH38/100/101-CO-FT signaling.

Loss of zebrafish atp6v1e1b, encoding a subunit of vacuolar ATPase, recapitulates human ARCL type 2C syndrome and identifies multiple pathobiological signatures

The inability to maintain a strictly regulated endo(lyso)somal acidic pH through the proton-pumping action of the vacuolar-ATPases (v-ATPases) has been associated with various human diseases including heritable connective tissue disorders. Autosomal recessive (AR) cutis laxa (CL) type 2C syndrome is associated with genetic defects in the ATP6V1E1 gene and is characterized by skin wrinkles or loose redundant skin folds with pleiotropic systemic manifestations. The underlying pathological mechanisms leading to the clinical presentations remain largely unknown. Here, we show that loss of atp6v1e1b in zebrafish leads to early mortality, associated with craniofacial dysmorphisms, vascular anomalies, cardiac dysfunction, N-glycosylation defects, hypotonia, and epidermal structural defects. These features are reminiscent of the phenotypic manifestations in ARCL type 2C patients. Our data demonstrates that loss of atp6v1e1b alters endo(lyso)somal protein levels, and interferes with non-canonical v-ATPase pathways in vivo. In order to gain further insights into the processes affected by loss of atp6v1e1b, we performed an untargeted analysis of the transcriptome, metabolome, and lipidome in early atp6v1e1b-deficient larvae. We report multiple affected pathways including but not limited to oxidative phosphorylation, sphingolipid, fatty acid, and energy metabolism together with profound defects on mitochondrial respiration. Taken together, our results identify complex pathobiological effects due to loss of atp6v1e1b in vivo.

Cutis laxa syndromes are pleiotropic disorders of the connective tissue, characterized by skin redundancy and variable systemic manifestations. Cutis laxa syndromes are caused by pathogenic variants in genes encoding structural and regulatory components of the extracellular matrix or in genes encoding components of cellular trafficking, metabolism, and mitochondrial function. Pathogenic variants in genes coding for vacuolar-ATPases, a multisubunit complex responsible for the acidification of multiple intracellular vesicles, cause type 2 cutis laxa syndromes, a group of cutis laxa subtypes further characterized by neurological, skeletal, and rarely cardiopulmonary manifestations. To investigate the pathomechanisms of vacuolar-ATPase dysfunction, we generated zebrafish models that lack a crucial subunit of the vacuolar-ATPases. The mutant zebrafish models show morphological and functional features reminiscent of the phenotypic manifestations in cutis laxa patients carrying pathogenic variants in ATP6V1E1. In-depth analysis at multiple -omic levels identified biological signatures that indicate impairment of signaling pathways, lipid metabolism, and mitochondrial respiration. We anticipate that these data will contribute to a better understanding of the pathogenesis of cutis laxa syndromes and other disorders involving defective v-ATPase function, which may eventually improve patient treatment and management.

Removal of H3K27me3 by JMJ Proteins Controls Plant Development and Environmental Responses in Arabidopsis

Trimethylation of histone H3 lysine 27 (H3K27me3) is a highly conserved repressive histone modification that signifies transcriptional repression in plants and animals. In Arabidopsis thaliana, the demethylation of H3K27 is regulated by a group of JUMONJI DOMAIN-CONTANING PROTEIN (JMJ) genes. Transcription of JMJ genes is spatiotemporally regulated during plant development and in response to the environment. Once JMJ genes are transcribed, recruitment of JMJs to target genes, followed by demethylation of H3K27, is critically important for the precise control of gene expression. JMJs function synergistically and antagonistically with transcription factors and/or other epigenetic regulators on chromatin. This review summarizes the latest advances in our understanding of Arabidopsis H3K27me3 demethylases that provide robust and flexible epigenetic regulation of gene expression to direct appropriate development and environmental responses in plants.

H3K27me3 demethylases alter HSP22 and HSP17.6C expression in response to recurring heat in Arabidopsis

Acclimation to high temperature increases plants' tolerance of subsequent lethal high temperatures. Although epigenetic regulation of plant gene expression is well studied, how plants maintain a memory of environmental changes over time remains unclear. Here, we show that JUMONJI (JMJ) proteins, demethylases involved in histone H3 lysine 27 trimethylation (H3K27me3), are necessary for Arabidopsis thaliana heat acclimation. Acclimation induces sustained H3K27me3 demethylation at HEAT SHOCK PROTEIN22 (HSP22) and HSP17.6C loci by JMJs, poising the HSP genes for subsequent activation. Upon sensing heat after a 3-day interval, JMJs directly reactivate these HSP genes. Finally, jmj mutants fail to maintain heat memory under fluctuating field temperature conditions. Our findings of an epigenetic memory mechanism involving histone demethylases may have implications for environmental adaptation of field plants.

Transcriptional Cascade in the Regulation of Flowering in the Bamboo Orchid Arundina graminifolia

Flowering in orchids is the most important horticultural trait regulated by multiple mechanisms. Arundina graminifolia flowers throughout the year unlike other orchids with a narrow flowering span. However, little is known of the genetic regulation of this peculiar flowering pattern. This study identifies a number of transcription factor (TF) families in five stages of flower development and four tissue types through RNA-seq transcriptome. About 700 DEGs were annotated to the transcription factor category and classified into 35 TF families, which were involved in multiple signaling pathways. The most abundant TF family was bHLH, followed by MYB and WRKY. Some important members of the bHLH, WRKY, MYB, TCP, and MADS-box families were found to regulate the flowering genes at transcriptional levels. Particularly, the TFs WRKY34 and ERF12 possibly respond to vernalization and photoperiod signaling, MYB108, RR9, VP1, and bHLH49 regulate hormonal balance, and CCA1 may control the circadian pathway. MADS-box TFs including MADS6, 14, 16, AGL5, and SEP may be important regulators of flowering in A. graminifolia. Therefore, this study provides a theoretical basis for understanding the molecular mechanism of flowering in A. graminifolia.

Distinct identities of leaf phloem cells revealed by single cell transcriptomics

The leaf vasculature plays a key role in solute translocation. Veins consist of at least seven distinct cell types, with specific roles in transport, metabolism, and signaling. Little is known about leaf vascular cells, in particular the phloem parenchyma (PP). PP effluxes sucrose into the apoplasm as a basis for phloem loading, yet PP has been characterized only microscopically. Here, we enriched vascular cells from Arabidopsis leaves to generate a single-cell transcriptome atlas of leaf vasculature. We identified at least 19 cell clusters, encompassing epidermis, guard cells, hydathodes, mesophyll, and all vascular cell types, and used metabolic pathway analysis to define their roles. Clusters comprising PP cells were enriched for transporters, including SWEET11 and SWEET12 sucrose and UmamiT amino acid efflux carriers. We provide evidence that PP development occurs independently from ALTERED PHLOEM DEVELOPMENT, a transcription factor required for phloem differentiation. PP cells have a unique pattern of amino acid metabolism activity distinct from companion cells (CCs), explaining differential distribution/metabolism of amino acids in veins. The kinship relation of the vascular clusters is strikingly similar to the vein morphology, except for a clear separation of CC from the other vascular cells including PP. In summary, our single-cell RNA-sequencing analysis provides a wide range of information into the leaf vasculature and the role and relationship of the leaf cell types.

Systematic analysis of JmjC gene family and stress--response expression of KDM5 subfamily genes in Brassica napus

Background

Jumonji C (JmjC) proteins exert critical roles in plant development and stress response through the removal of lysine methylation from histones. Brassica napus, which originated from spontaneous hybridization by Brassica rapa and Brassica oleracea, is the most important oilseed crop after soybean. In JmjC proteins of Brassica species, the structure and function and its relationship with the parents and model plant Arabidopsis thaliana remain uncharacterized. Systematic identification and analysis for JmjC family in Brassica crops can facilitate the future functional characterization and oilseed crops improvement.

Methods

Basing on the conserved JmjC domain, JmjC homologs from the three Brassica species, B. rapa (AA), B. oleracea (CC) and B. napus, were identified from the Brassica database. Some methods, such as phylogenic analysis, chromosomal mapping, HMMER searching, gene structure display and Logos analysis, were used to characterize relationships of the JmjC homologs. Synonymous and nonsynonymous nucleotide substitutions were used to infer the information of gene duplication among homologs. Then, the expression levels of BnKDM5 subfamily genes were checked under abiotic stress by qRT-PCR.

Results

Sixty-five JmjC genes were identified from B. napus genome, 29 from B. rapa, and 23 from B. oleracea. These genes were grouped into seven clades based on the phylogenetic analysis, and their catalytic activities of demethylation were predicted. The average retention rate of B. napus JmjC genes (B. napus JmjC gene from B. rapa (93.1%) and B. oleracea (82.6%)) exceeded whole genome level. JmjC sequences demonstrated high conservation in domain origination, chromosomal location, intron/exon number and catalytic sites. The gene duplication events were confirmed among the homologs. Many of the BrKDM5 subfamily genes showed higher expression under drought and NaCl treatments, but only a few genes were involved in high temperature stress.

Conclusions

This study provides the first genome-wide characterization of JmjC genes in Brassica species. The BnJmjC exhibits higher conservation during the formation process of allotetraploid than the average retention rates of the whole B. napus genome. Furthermore, expression profiles of many genes indicated that BnKDM5 subfamily genes are involved in stress response to salt, drought and high temperature.