A genome-scale resource for the functional characterization of Arabidopsis transcription factors

Exploring the nexus of cGAS STING pathway in neurodegenerative terrain: A therapeutic odyssey

By detecting and responding to cytosolic DNA, the cGAS STING pathway regulates the innate immune responses bymediatinginflammatory reactions and antiviral defense. Thederegulation and modification of this system have been linked to variousneurodegenerative diseases like AD, PD and ALS. Accumulation of tau protein and Aβ aggregates to activate the pathway and releases neuroinflammatory cytokines which accelerates neuronal dysfunction and cognitive impairment as the symptom of AD. Similarly, in PD Alpha-synuclein aggregates activate the cGAS STING pathway and regulate the neuroinflammation and oxidative stress. In ALS, mutation of the genes causes the activation of the pathway which leads to motor neuron degeneration. Alteration of the cGAS STING pathway also leads to mitochondrial dysfunction and impaired autophagy. Preclinical investigations of AD, PD, and ALS animal models showed that STING pathway inhibitors reduced inflammation and improved neurological outcomes and modulators of the cGAS STING pathway may treat these neurodegenerative disorders. In this review we focus on the fact thatneuroinflammation, neuronal dysfunction, and various disease progressions can be treated byaltering the cGAS STING pathway. Understanding the processes and creating specific interventions for this route may offer new treatments for these terrible illnesses.

GLABRA2 transcription factor integrates arsenic tolerance with epidermal cell fate determination

Arsenic poses a global threat to living organisms, compromising crop security and yield. Limited understanding of the transcriptional network integrating arsenic-tolerance mechanisms with plant developmental responses hinders the development of strategies against this toxic metalloid. Here, we conducted a high-throughput yeast one-hybrid assay using as baits the promoter region from the arsenic-inducible genes ARQ1 and ASK18 from Arabidopsis thaliana, coupled with a transcriptomic analysis, to uncover novel transcriptional regulators of the arsenic response. We identified the GLABRA2 (GL2) transcription factor as a novel regulator of arsenic tolerance, revealing a wider regulatory role beyond its established function as a repressor of root hair formation. Furthermore, we found that ANTHOCYANINLESS2 (ANL2), a GL2 subfamily member, acts redundantly with this transcription factor in the regulation of arsenic signaling. Both transcription factors act as repressors of arsenic response. gl2 and anl2 mutants exhibit enhanced tolerance and reduced arsenic accumulation. Transcriptional analysis in the gl2 mutant unveils potential regulators of arsenic tolerance. These findings highlight GL2 and ANL2 as novel integrators of the arsenic response with developmental outcomes, offering insights for developing safer crops with reduced arsenic content and increased tolerance to this hazardous metalloid.

Complex control of seed germination timing by ERF50 involves RGL2 antagonism and negative feedback regulation of DOG1

Seed dormancy governs germination timing, with both evolutionary and applied consequences. Despite extensive studies on the hormonal and genetic control of these processes, molecular mechanisms directly linking dormancy and germination remain poorly understood. By screening a collection of lines overexpressing Arabidopsis transcription factors, we identified ERF50 as a key gene to control dormancy and germination. To study its regulation, we measured seed-related physiological parameters in loss-of-function mutants and carried out transactivation, protein interaction and ChIP-PCR analyses. We found direct ERF50-mediated repression of DOG1 and activation of EXPA2 transcription, which results in enhanced seed germination. Although ERF50 expression is increased by DOG1 in dormant seeds, ERF50 germination-promoting activity is blocked by RGL2. The physiological, genetic and molecular evidence gathered here supports that ERF50 controls germination timing by regulating DOG1 levels to leverage its role as enhancer of seed germination, via RGL2 antagonism on EXPA2 expression. Our results highlight the central role of ERF50 as a feedback regulator to couple and fine-tune seed dormancy and germination.

ACRE, a class of AP2/ERF transcription factors, activates the expression of sweet potato ß-amylase and sporamin genes through the sugar-responsible element CMSRE-1

Sugars, synthesized by photosynthesis in source organs, are loaded and utilized as an energy source and carbon skeleton in sink organs, and also known to be important signal molecules regulating gene expression in higher plants. The expression of genes coding for sporamin and β-amylase, the two most abundant proteins in storage roots of sweet potato, is coordinately induced by sugars. We previously reported on the identification of the carbohydrate metabolic signal-responsible element-1 (CMSRE-1) essential for the sugar-responsible expression of two genes. However, transcription factors that bind to this sequence have not been identified. In this study, we performed yeast one-hybrid screening using the sugar-responsible minimal promoter region of the ß-amylase gene as bait and a library composed only transcription factor cDNAs of Arabidopsis. Two clones, named Activator protein binding to CMSRE-1 (ACRE), encoding AP2/ERF transcription factors were isolated. ACRE showed transactivation activity of the sugar-responsible minimal promoter in a CMSRE-1-dependent manner in Arabidopsis protoplasts. Electric mobility shift assay (EMSA) using recombinant proteins and transient co-expression assay in Arabidopsis protoplasts revealed that ACRE could actually act to the CMSRE-1. Among the DEHYDRATION -RESPONSIVE ELEMENT BINDING FACTOR (DREB) subfamily, almost all homologs including ACRE, could act on the DRE, while only three ACREs could act to the CMSRE-1. Moreover, ACRE-homologs of Japanese morning glory also have the same property of DNA-binding preference and transactivation activity through the CMSRE-1. These findings suggested that ACRE plays an important role in the mechanism regulating the sugar-responsible gene expression through the CMSRE-1 conserved across plant species.

The dual role of the RETINOBLASTOMA-RELATED protein in the DNA damage response is coordinated by the interaction with LXCXE-containing proteins

Living organisms possess mechanisms to safeguard genome integrity. To avoid spreading mutations, DNA lesions are detected and cell division is temporarily arrested to allow repair mechanisms. Afterward, cells either resume division or respond to unsuccessful repair by undergoing programmed cell death (PCD). How the success rate of DNA repair connects to later cell fate decisions remains incompletely known, particularly in plants. The Arabidopsis thaliana RETINOBLASTOMA-RELATED1 (RBR) protein and its partner E2FA, play both structural and transcriptional functions in the DNA damage response (DDR). Here we provide evidence that distinct RBR protein interactions with LXCXE motif-containing proteins guide these processes. Using the N849F substitution in the RBR B-pocket domain, which specifically disrupts binding to the LXCXE motif, we show that these interactions are dispensable in unchallenging conditions. However, N849F substitution abolishes RBR nuclear foci and promotes PCD and growth arrest upon genotoxic stress. NAC044, which promotes growth arrest and PCD, accumulates after the initial recruitment of RBR to foci and can bind non-focalized RBR through the LXCXE motif in a phosphorylation-independent manner, allowing interaction at different cell cycle phases. Disrupting NAC044-RBR interaction impairs PCD, but their genetic interaction points to opposite independent roles in the regulation of PCD. The LXCXE-binding dependency of the roles of RBR in the DDR suggests a coordinating mechanism to translate DNA repair success to cell survival. We propose that RBR and NAC044 act in two distinct DDR pathways, but interact to integrate input from both DDR pathways to decide upon an irreversible cell fate decision.

Dissection of the IDA promoter identifies WRKY transcription factors as abscission regulators in Arabidopsis

Plants shed organs such as leaves, petals, or fruits through the process of abscission. Monitoring cues such as age, resource availability, and biotic and abiotic stresses allow plants to abscise organs in a timely manner. How these signals are integrated into the molecular pathways that drive abscission is largely unknown. The INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) gene is one of the main drivers of floral organ abscission in Arabidopsis and is known to transcriptionally respond to most abscission-regulating cues. By interrogating the IDA promoter in silico and in vitro, we identified transcription factors that could potentially modulate IDA expression. We probed the importance of ERF- and WRKY-binding sites for IDA expression during floral organ abscission, with WRKYs being of special relevance to mediate IDA up-regulation in response to biotic stress in tissues destined for separation. We further characterized WRKY57 as a positive regulator of IDA and IDA-like gene expression in abscission zones. Our findings highlight the promise of promoter element-targeted approaches to modulate the responsiveness of the IDA signaling pathway to harness controlled abscission timing for improved crop productivity.

Root branching under high salinity requires auxin-independent modulation of LATERAL ORGAN BOUNDARY DOMAIN 16 function

Salinity stress constrains lateral root (LR) growth and severely affects plant growth. Auxin signaling regulates LR formation, but the molecular mechanism by which salinity affects root auxin signaling and whether salt induces other pathways that regulate LR development remains unknown. In Arabidopsis thaliana, the auxin-regulated transcription factor LATERAL ORGAN BOUNDARY DOMAIN 16 (LBD16) is an essential player in LR development under control conditions. Here, we show that under high-salt conditions, an alternative pathway regulates LBD16 expression. Salt represses auxin signaling but, in parallel, activates ZINC FINGER OF ARABIDOPSIS THALIANA 6 (ZAT6), a transcriptional activator of LBD16. ZAT6 activates LBD16 expression, thus contributing to downstream cell wall remodeling and promoting LR development under high-salt conditions. Our study thus shows that the integration of auxin-dependent repressive and salt-activated auxin-independent pathways converging on LBD16 modulates root branching under high-salt conditions.

The interplay between the circadian clock and abiotic stress responses mediated by ABF3 and CCA1/LHY

Climate change is a global concern for all life on our planet, including humans and plants. Plants' growth and development are significantly affected by abiotic stresses, including adverse temperature, inadequate or excess water availability, nutrient deficiency, and salinity. The circadian clock is a master regulator of numerous developmental and metabolic processes in plants. In an effort to identify new clock-related genes and outputs through bioinformatic analysis, we have revealed that CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) play a crucial role in regulating a wide range of abiotic stress responses and target ABSCISIC ACID RESPONSIVE ELEMENTS-BINDING FACTOR3 (ABF3), a key transcription factor in the plant hormone Abscisic acid (ABA)-signaling pathway. Specifically, we found that CCA1 and LHY regulate the expression of ABF3 under diel conditions, as well as seed germination under salinity. Conversely, ABF3 controls the expression of core clock genes and orchestrates the circadian period in a stress-responsive manner. ABF3 delivers the stress signal to the central oscillator by binding to the promoter of CCA1 and LHY. Overall, our study uncovers the reciprocal regulation between ABF3 and CCA1/LHY and molecular mechanisms underlying the interaction between the circadian clock and abiotic stress. This finding may aid in developing molecular and genetic solutions for plants to survive and thrive in the face of climate change.

Protein interaction mapping reveals widespread targeting of development-related host transcription factors by phytoplasma effectors

Phytoplasmas are pathogenic bacteria that reprogram plant host development for their own benefit. Previous studies have characterized a few different phytoplasma effector proteins that destabilize specific plant transcription factors. However, these are only a small fraction of the potential effectors used by phytoplasmas; therefore, the molecular mechanisms through which phytoplasmas modulate their hosts require further investigation. To obtain further insights into the phytoplasma infection mechanisms, we generated a protein-protein interaction network between a broad set of phytoplasma effectors and a large, unbiased collection of Arabidopsis thaliana transcription factors and transcriptional regulators. We found widespread, but specific, interactions between phytoplasma effectors and host transcription factors, especially those related to host developmental processes. In particular, many unrelated effectors target specific sets of TCP transcription factors, which regulate plant development and immunity. Comparison with other host-pathogen protein interaction networks shows that phytoplasma effectors have unusual targets, indicating that phytoplasmas have evolved a unique and unusual infection strategy. This study contributes a rich and solid data source that guides further investigations of the functions of individual effectors, as demonstrated for some herein. Moreover, the dataset provides insights into the underlying molecular mechanisms of phytoplasma infection.

Conserved plant transcriptional responses to microgravity from two consecutive spaceflight experiments

Introduction

Understanding how plants adapt to the space environment is essential, as plants will be a valuable component of long duration space missions. Several spaceflight experiments have focused on transcriptional profiling as a means of understanding plant adaptation to microgravity. However, there is limited overlap between results from different experiments. Differences in experimental conditions and hardware make it difficult to find a consistent response across experiments and to distinguish the primary effects of microgravity from other spaceflight effects.

Methods

Plant Signaling (PS) and Plant RNA Regulation (PRR) were two separate spaceflight experiments conducted on the International Space Station utilizing the European Modular Cultivation System (EMCS). The EMCS provided a lighted environment for plant growth with centrifugal capabilities providing an onboard 1 g control.

Results and discussion

An RNA-Seq analysis of shoot samples from PS and PRR revealed a significant overlap of genes differentially expressed in microgravity between the two experiments. Relative to onboard 1 g controls, genes involved in transcriptional regulation, shoot development, and response to auxin and light were upregulated in microgravity in both experiments. Conversely, genes involved in defense response, abiotic stress, Ca++ signaling, and cell wall modification were commonly downregulated in both datasets. The downregulation of stress responses in microgravity in these two experiments is interesting as these pathways have been previously observed as upregulated in spaceflight compared to ground controls. Similarly, we have observed many stress response genes to be upregulated in the 1 g onboard control compared to ground reference controls; however these genes were specifically downregulated in microgravity. In addition, we analyzed the sRNA landscape of the 1 g and microgravity (μ g) shoot samples from PRR. We identified three miRNAs (miR319c, miR398b, and miR8683) which were upregulated in microgravity, while several of their corresponding target genes were found to be downregulated in microgravity. Interestingly, the downregulated target genes are enriched in those encoding chloroplast-localized enzymes and proteins. These results uncover microgravity unique transcriptional changes and highlight the validity and importance of an onboard 1 g control.

Large-scale identification of novel transcriptional regulators of the aliphatic glucosinolate pathway in Arabidopsis

Aliphatic glucosinolates are a large group of plant secondary metabolites characteristic of Brassicaceae, including the model plant Arabidopsis. The diverse and complex degradation products of aliphatic glucosinolates contribute to plant responses to herbivory, pathogen attack, and environmental stresses. Most of the biosynthesis genes in the aliphatic glucosinolate pathway have been cloned in Arabidopsis, and the research focus has recently shifted to the regulatory mechanisms controlling aliphatic glucosinolate accumulation. Up till now, more than 40 transcriptional regulators have been identified as regulating the aliphatic glucosinolate pathway, but many more novel regulators likely remain to be discovered based on research evidence over the past decade. In the current study, we took a systemic approach to functionally test 155 candidate transcription factors in Arabidopsis identified by yeast one-hybrid assay, and successfully validated at least 30 novel regulators that could significantly influence the accumulation of aliphatic glucosinolates in our experimental set-up. We also showed that the regulators of the aliphatic glucosinolate pathway have balanced positive and negative effects, and glucosinolate metabolism and plant development can be coordinated. Our work is the largest scale effort so far to validate transcriptional regulators of a plant secondary metabolism pathway, and provides new insights into how the highly diverse plant secondary metabolism is regulated at the transcriptional level.

Arabidopsis BBX14 negatively regulates nitrogen starvation- and dark-induced leaf senescence

Senescence is a highly regulated process driven by developmental age and environmental factors. Although leaf senescence is accelerated by nitrogen (N) deficiency, the underlying physiological and molecular mechanisms are largely unknown. Here, we reveal that BBX14, a previously uncharacterized BBX-type transcription factor in Arabidopsis, is crucial for N starvation-induced leaf senescence. We find that inhibiting BBX14 by artificial miRNA (amiRNA) accelerates senescence during N starvation and in darkness, while BBX14 overexpression (BBX14-OX) delays it, identifying BBX14 as a negative regulator of N starvation- and dark-induced senescence. During N starvation, nitrate and amino acids like glutamic acid, glutamine, aspartic acid, and asparagine were highly retained in BBX14-OX leaves compared to the wild type. Transcriptome analysis showed a large number of senescence-associated genes (SAGs) to be differentially expressed between BBX14-OX and wild-type plants, including ETHYLENE INSENSITIVE3 (EIN3) which regulates N signaling and leaf senescence. Chromatin immunoprecipitation (ChIP) showed that BBX14 directly regulates EIN3 transcription. Furthermore, we revealed the upstream transcriptional cascade of BBX14. By yeast one-hybrid screen and ChIP, we found that MYB44, a stress-responsive MYB transcription factor, directly binds to the promoter of BBX14 and activates its expression. In addition, Phytochrome Interacting Factor 4 (PIF4) binds to the promoter of BBX14 to repress BBX14 transcription. Thus, BBX14 functions as a negative regulator of N starvation-induced senescence through EIN3 and is directly regulated by PIF4 and MYB44.

Distinct early transcriptional regulations by turgor and osmotic potential in the roots of Arabidopsis

In a context of climate change, deciphering signaling pathways driving plant adaptation to drought, changes in water availability, and salt is key. A crossing point of these plant stresses is their impact on plant water potential (Ψ), a composite physico-chemical variable reflecting the availability of water for biological processes such as plant growth and stomatal aperture. The Ψ of plant cells is mainly driven by their turgor and osmotic pressures. Here we investigated the effect of a variety of osmotic treatments on the roots of Arabidopsis plants grown in hydroponics. We used, among others, a permeating solute as a way to differentiate variations on turgor from variations in osmotic pressure. Measurement of cortical cell turgor pressure with a cell pressure probe allowed us to monitor the intensity of the treatments and thereby preserve the cortex from plasmolysis. Transcriptome analyses at an early time point (15 min) showed specific and quantitative transcriptomic responses to both osmotic and turgor pressure variations. Our results highlight how water-related biophysical parameters can shape the transcriptome of roots under stress and provide putative candidates to explore further the early perception of water stress in plants.

ERFVII transcription factors and their role in the adaptation to hypoxia in Arabidopsis and crops

In this review, we focus on ethylene transcription factors (ERFs), which are a crucial family of transcription factors that regulate plant development and stress responses. ERFVII transcription factors have been identified and studied in several crop species, including rice, wheat, maize, barley, and soybean. These transcription factors are known to be involved in regulating the plant's response to low oxygen stress-hypoxia and could thus improve crop yields under suboptimal growing conditions. In rice (Oryza sativa) several ERFVII genes have been identified and characterized, including SUBMERGENCE 1A (SUB1A), which enables rice to tolerate submergence. The SUB1A gene was used in the development of SUB1 rice varieties, which are now widely grown in flood-prone areas and have been shown to improve yields and farmer livelihoods. The oxygen sensor in plants was discovered using the model plant Arabidopsis. The mechanism is based on the destabilization of ERFVII protein via the N-degron pathway under aerobic conditions. During hypoxia, the stabilized ERFVIIs translocate to the nucleus where they activate the transcription of hypoxia-responsive genes (HRGs). In summary, the identification and characterization of ERFVII transcription factors and their mechanism of action could lead to the development of new crop varieties with improved tolerance to low oxygen stress, which could have important implications for global food security.

Enhancer activation via TCP and HD-ZIP and repression by Dof transcription factors mediate giant cell-specific expression

Proper cell-type identity relies on highly coordinated regulation of gene expression. Regulatory elements such as enhancers can produce cell type-specific expression patterns, but the mechanisms underlying specificity are not well understood. We previously identified an enhancer region capable of driving specific expression in giant cells, which are large, highly endoreduplicated cells in the Arabidopsis thaliana sepal epidermis. In this study, we use the giant cell enhancer as a model to understand the regulatory logic that promotes cell type-specific expression. Our dissection of the enhancer revealed that giant cell specificity is mediated primarily through the combination of two activators and one repressor. HD-ZIP and TCP transcription factors are involved in the activation of expression throughout the epidermis. High expression of HD-ZIP transcription factor genes in giant cells promoted higher expression driven by the enhancer in giant cells. Dof transcription factors repressed the activity of the enhancer such that only giant cells maintained enhancer activity. Thus, our data are consistent with a conceptual model whereby cell type-specific expression emerges from the combined activities of three transcription factor families activating and repressing expression in epidermal cells.

BBX24 Interacts with JAZ3 to Promote Growth by Reducing DELLA Activity in Shade Avoidance

Shade avoidance syndrome (SAS) is a strategy of major adaptive significance and typically includes elongation of the stem and petiole, leaf hyponasty, reduced branching and phototropic orientation of the plant shoot toward canopy gaps. Both cryptochrome 1 and phytochrome B (phyB) are the major photoreceptors that sense the reduction in the blue light fluence rate and the low red:far-red ratio, respectively, and both light signals are associated with plant density and the resource reallocation when SAS responses are triggered. The B-box (BBX)-containing zinc finger transcription factor BBX24 has been implicated in the SAS as a regulator of DELLA activity, but this interaction does not explain all the observed BBX24-dependent regulation in shade light. Here, through a combination of transcriptional meta-analysis and large-scale identification of BBX24-interacting transcription factors, we found that JAZ3, a jasmonic acid signaling component, is a direct target of BBX24. Furthermore, we demonstrated that joint loss of BBX24 and JAZ3 function causes insensitivity to DELLA accumulation, and the defective shade-induced elongation in this mutant is rescued by loss of DELLA or phyB function. Therefore, we propose that JAZ3 is part of the regulatory network that controls the plant growth in response to shade, through a mechanism in which BBX24 and JAZ3 jointly regulate DELLA activity. Our results provide new insights into the participation of BBX24 and JA signaling in the hypocotyl shade avoidance response in Arabidopsis.

Brassinosteroid gene regulatory networks at cellular resolution in the Arabidopsis root

Brassinosteroids are plant steroid hormones that regulate diverse processes, such as cell division and cell elongation, through gene regulatory networks that vary in space and time. By using time series single-cell RNA sequencing to profile brassinosteroid-responsive gene expression specific to different cell types and developmental stages of the Arabidopsis root, we identified the elongating cortex as a site where brassinosteroids trigger a shift from proliferation to elongation associated with increased expression of cell wall-related genes. Our analysis revealed HOMEOBOX FROM ARABIDOPSIS THALIANA 7 (HAT7) and GT-2-LIKE 1 (GTL1) as brassinosteroid-responsive transcription factors that regulate cortex cell elongation. These results establish the cortex as a site of brassinosteroid-mediated growth and unveil a brassinosteroid signaling network regulating the transition from proliferation to elongation, which illuminates aspects of spatiotemporal hormone responses.

A gene silencing screen uncovers diverse tools for targeted gene repression in Arabidopsis

DNA methylation has been utilized for target gene silencing in plants. However, it is not well understood whether other silencing pathways can be also used to manipulate gene expression. Here we performed a gain-of-function screen for proteins that could silence a target gene when fused to an artificial zinc finger. We uncovered many proteins that suppressed gene expression through DNA methylation, histone H3K27me3 deposition, H3K4me3 demethylation, histone deacetylation, inhibition of RNA polymerase II transcription elongation or Ser-5 dephosphorylation. These proteins also silenced many other genes with different efficacies, and a machine learning model could accurately predict the efficacy of each silencer on the basis of various chromatin features of the target loci. Furthermore, some proteins were also able to target gene silencing when used in a dCas9-SunTag system. These results provide a more comprehensive understanding of epigenetic regulatory pathways in plants and provide an armament of tools for targeted gene manipulation.

Transcriptional Reactivation of Lignin Biosynthesis for the Heterologous Production of Etoposide Aglycone in Nicotiana benthamiana

Nicotiana benthamiana is a valuable plant chassis for heterologous production of medicinal plant natural products. This host is well suited for the processing of organelle-localized plant enzymes, and the conservation of the primary metabolism across the plant kingdom often provides required plant-specific precursor molecules that feed a given pathway. Despite this commonality in metabolism, limited precursor supply and/or competing host pathways can interfere with yields of heterologous products. Here, we use transient transcriptional reprogramming of endogenous N. benthamiana metabolism to drastically improve flux through the etoposide pathway derived from the medicinal plant Podophyllum spp. Specifically, coexpression of a single lignin-associated transcription factor, MYB85, with pathway genes results in unprecedented levels of heterologous product accumulation in N. benthamiana leaves: 1 mg/g dry weight (DW) of the etoposide aglycone, 35 mg/g DW (-)-deoxypodophyllotoxin, and 3.5 mg/g DW (-)-epipodophyllotoxin─up to two orders of magnitude above previously reported biosynthetic yields for the etoposide aglycone and eight times higher than what is observed for (-)-deoxypodophyllotoxin in the native medicinal plant. Unexpectedly, transient activation of lignin metabolism by transcription factor overexpression also reduces the production of undesired side products that likely result from competing N. benthamiana metabolism. Our work demonstrates that synthetic activation of lignin biosynthesis in leaf tissue is an effective strategy for optimizing the production of medicinal compounds derived from phenylpropanoid precursors in the plant chassis N. benthamiana. Furthermore, our results highlight the engineering value of MYB85, an early switch in lignin biosynthesis, for on-demand modulation of monolignol flux and support the role of MYB46 as a master regulator of lignin polymer deposition.

CAST-R: An application to visualize circadian and heat stress-responsive genes in plants

The circadian clock helps organisms to anticipate and coordinate gene regulatory responses to changes in environmental stimuli. Under stresses, both time of day and the circadian clock closely control the magnitude of plant responses. The identification of clock-regulated genes is, therefore, important when studying the influence of environmental factors. Here, we present CAST-R (Circadian And heat STress-Responsive), a "Shiny" application that allows users to identify and visualize circadian and heat stress-responsive genes in plants. More specifically, users can generate and export profiles and heatmaps representing transcript abundance of a single or of multiple Arabidopsis (Arabidopsis thaliana) genes over a 24-h time course, in response to heat stress and during recovery following the stress. The application also takes advantage of published Arabidopsis chromatin immunoprecipitation-sequencing datasets to visualize the connections between clock proteins and their targets in an interactive network. In addition, CAST-R offers the possibility to perform phase (i.e. timing of expression) enrichment analyses for rhythmic datasets from any species, within and beyond plants. This functionality combines statistical analyses and graphical representations to identify significantly over- and underrepresented phases within a subset of genes. Lastly, profiles of transcript abundance can be visualized from multiple circadian datasets generated in Arabidopsis, Brassica rapa, barley (Hordeum vulgare), and rice (Oryza sativa). In summary, CAST-R is a user-friendly interface that allows the rapid identification of circadian and stress-responsive genes through multiple modules of visualization. We anticipate that this tool will make it easier for users to obtain temporal and dynamic information on genes of interest that links plant responses to environmental signals.

Genome-wide identification of the TGA gene family in kiwifruit (Actinidia chinensis spp.) and revealing its roles in response to Pseudomonas syringae pv. actinidiae (Psa) infection

Kiwifruit bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa), is a destructive disease of kiwifruit worldwide. Functional genes in response to Psa infection are needed, as they could be utilized to control disease. TGACG-binding transcription factor (TGA), as an essential regulator, involved in the process of plant against pathogens. However, the function of TGA regulators has not been reported in kiwifruit. It is unclear that whether TGA genes play a role in response to Psa infection. Here, we performed genome-wide screening and identified 13 TGA genes in kiwifruit. Phylogenetic analysis showed that 13 members of the AcTGA gene family could be divided into five groups. AcTGA proteins were mainly located in the nucleus, and significant differences were identified in their 3D structures. Segmental duplications promoted the expansion of the AcTGA family. Additionally, RNA-Seq and qRT-PCR revealed that four genes (AcTGA01/06/07/09) were tissue-specific and responsive to hormones at different levels. Subcellular localization showed that four proteins located in the nucleus, and among them, three (AcTGA01/06/07) had transcriptional activation activity. Lastly, transient overexpression proved that these three genes (AcTGA01/06/07) potentially played a role in the resistance to kiwifruit canker. These results provided a theoretical basis for revealing TGA involved in kiwifruit regulation against Psa.

The TCP transcription factor HvTB2 heterodimerizes with VRS5 and controls spike architecture in barley

Understanding the molecular network, including protein-protein interactions, of VRS5 provide new routes towards the identification of other key regulators of plant architecture in barley. The TCP transcriptional regulator TEOSINTE BRANCHED 1 (TB1) is a key regulator of plant architecture. In barley, an important cereal crop, HvTB1 (also referred to as VULGARE SIX-ROWED spike (VRS) 5), inhibits the outgrowth of side shoots, or tillers, and grains. Despite its key role in barley development, there is limited knowledge on the molecular network that is utilized by VRS5. In this work, we performed protein-protein interaction studies of VRS5. Our analysis shows that VRS5 potentially interacts with a diverse set of proteins, including other class II TCP's, NF-Y TF, but also chromatin remodelers. Zooming in on the interaction capacity of VRS5 with other TCP TFs shows that VRS5 preferably interacts with other class II TCP TFs in the TB1 clade. Induced mutagenesis through CRISPR-Cas of one of the putative VRS5 interactors, HvTB2 (also referred to as COMPOSITUM 1 and BRANCHED AND INDETERMINATE SPIKELET 1), resulted in plants that have lost their characteristic unbranched spike architecture. More specifically, hvtb2 mutants exhibited branches arising at the main spike, suggesting that HvTB2 acts as inhibitor of branching. Our protein-protein interaction studies of VRS5 resulted in the identification of HvTB2 as putative interactor of VRS5, another key regulator of spike architecture in barley. The study presented here provides a first step to underpin the protein-protein interactome of VRS5 and to identify other, yet unknown, key regulators of barley plant architecture.

CisCross: A gene list enrichment analysis to predict upstream regulators in Arabidopsis thaliana

Having DNA-binding profiles for a sufficient number of genome-encoded transcription factors (TFs) opens up the perspectives for systematic evaluation of the upstream regulators for the gene lists. Plant Cistrome database, a large collection of TF binding profiles detected using the DAP-seq method, made it possible for Arabidopsis. Here we re-processed raw DAP-seq data with MACS2, the most popular peak caller that leads among other ones according to quality metrics. In the benchmarking study, we confirmed that the improved collection of TF binding profiles supported a more precise gene list enrichment procedure, and resulted in a more relevant ranking of potential upstream regulators. Moreover, we consistently recovered the TF binding profiles that were missing in the previous collection of DAP-seq peak sets. We developed the CisCross web service (https://plamorph.sysbio.ru/ciscross/) that gives more flexibility in the analysis of potential upstream TF regulators for Arabidopsis thaliana genes.

Integrated omics reveal novel functions and underlying mechanisms of the receptor kinase FERONIA in Arabidopsis thaliana

The receptor kinase FERONIA (FER) is a versatile regulator of plant growth and development, biotic and abiotic stress responses, and reproduction. To gain new insights into the molecular interplay of these processes and to identify new FER functions, we carried out quantitative transcriptome, proteome, and phosphoproteome profiling of Arabidopsis (Arabidopsis thaliana) wild-type and fer-4 loss-of-function mutant plants. Gene ontology terms for phytohormone signaling, abiotic stress, and biotic stress were significantly enriched among differentially expressed transcripts, differentially abundant proteins, and/or misphosphorylated proteins, in agreement with the known roles for FER in these processes. Analysis of multiomics data and subsequent experimental evidence revealed previously unknown functions for FER in endoplasmic reticulum (ER) body formation and glucosinolate biosynthesis. FER functions through the transcription factor NAI1 to mediate ER body formation. FER also negatively regulates indole glucosinolate biosynthesis, partially through NAI1. Furthermore, we found that a group of abscisic acid (ABA)-induced transcription factors is hypophosphorylated in the fer-4 mutant and demonstrated that FER acts through the transcription factor ABA INSENSITIVE5 (ABI5) to negatively regulate the ABA response during cotyledon greening. Our integrated omics study, therefore, reveals novel functions for FER and provides new insights into the underlying mechanisms of FER function.

The bZIP Transcription Factor Family in Adzuki Bean (Vigna Angularis): Genome-Wide Identification, Evolution, and Expression Under Abiotic Stress During the Bud Stage

Adzuki bean (Vigna angularis) is an important dietary legume crop that was first cultivated and domesticated in Asia. Currently, little is known concerning the evolution and expression patterns of the basic leucine zipper (bZIP) family transcription factors in the adzuki bean. Through the PFAM search, 72 bZIP members of adzuki bean (VabZIP) were identified from the reference genome. Most of them were located on 11 chromosomes and seven on an unknown chromosome. A comprehensive analysis, including evolutionary, motifs, gene structure, cis-elements, and collinearity was performed to identify VabZIP members. The subcellular localization results showed VabZIPs might locate on the nuclear. Quantitative real-time PCR (qRT-PCR) analysis of the relative expression of VabZIPs in different tissues at the bud stage revealed that VabZIPs had a tissue-specific expression pattern, and its expression was influenced by abiotic stress. These characteristics of VabZIPs provide insights for future research aimed at developing interventions to improve abiotic stress resistance.

Transcription factor dynamics in plants: Insights and technologies for in vivo imaging

Biochemical and genetic approaches have been extensively used to study transcription factor (TF) functions, but their dynamic behaviors and the complex ways in which they regulate transcription in plant cells remain unexplored, particularly behaviors such as translocation and binding to DNA. Recent developments in labeling and imaging techniques provide the necessary sensitivity and resolution to study these behaviors in living cells. In this review, we present an up-to-date portrait of the dynamics and regulation of TFs under physiologically relevant conditions and then summarize recent advances in fluorescent labeling strategies and imaging techniques. We then discuss future prospects and challenges associated with the application of these techniques to examine TFs' intricate dance in living plants.

Transcriptional competition shapes proteotoxic ER stress resolution

Through dynamic activities of conserved master transcription factors (mTFs), the unfolded protein response (UPR) relieves proteostasis imbalance of the endoplasmic reticulum (ER), a condition known as ER stress^1,2. Because dysregulated UPR is lethal, the competence for fate changes of the UPR mTFs must be tightly controlled^3,4. However, the molecular mechanisms underlying regulatory dynamics of mTFs remain largely elusive. Here, we identified the abscisic acid-related regulator G-class bZIP TF2 (GBF2) and the cis-regulatory element G-box as regulatory components of the plant UPR led by the mTFs, bZIP28 and bZIP60. We demonstrate that, by competing with the mTFs at G-box, GBF2 represses UPR gene expression. Conversely, a gbf2 null mutation enhances UPR gene expression and suppresses the lethality of a bzip28 bzip60 mutant in unresolved ER stress. By demonstrating that GBF2 functions as a transcriptional repressor of the UPR, we address the long-standing challenge of identifying shared signalling components for a better understanding of the dynamic nature and complexity of stress biology. Furthermore, our results identify a new layer of UPR gene regulation hinged upon an antagonistic mTFs-GFB2 competition for proteostasis and cell fate determination.

Mutations that alter Arabidopsis flavonoid metabolism affect the circadian clock

Flavonoids are a well-known class of specialized metabolites that play key roles in plant development, reproduction, and survival. Flavonoids are also of considerable interest from the perspective of human health, as both phytonutrients and pharmaceuticals. RNA sequencing analysis of an Arabidopsis null allele for chalcone synthase (CHS), which catalyzes the first step in flavonoid metabolism, has uncovered evidence that these compounds influence the expression of genes associated with the plant circadian clock. Analysis of promoter-luciferase constructs further showed that the transcriptional activity of CCA1 and TOC1, two key clock genes, is altered in CHS-deficient seedlings across the day/night cycle. Similar findings for a mutant line lacking flavonoid 3'-hydroxylase (F3'H) activity, and thus able to synthesize mono- but not dihydroxylated B-ring flavonoids, suggests that the latter are at least partially responsible; this was further supported by the ability of quercetin to enhance CCA1 promoter activity in wild-type and CHS-deficient seedlings. The effects of flavonoids on circadian function were also reflected in photosynthetic activity, with chlorophyll cycling abolished in CHS- and F3'H-deficient plants. Remarkably, the same phenotype was exhibited by plants with artificially high flavonoid levels, indicating that neither the antioxidant potential nor the light-screening properties of flavonoids contribute to optimal clock function, as has recently also been demonstrated in animal systems. Collectively, the current experiments point to a previously unknown connection between flavonoids and circadian cycling in plants and open the way to better understanding of the molecular basis of flavonoid action.

ORA47 is a transcriptional regulator of a general stress response hub

Transcriptional regulators of the general stress response (GSR) reprogram the expression of selected genes to transduce informational signals into cellular events, ultimately manifested in a plant's ability to cope with environmental challenges. Identification of the core GSR regulatory proteins will uncover the principal modules and their mode of action in the establishment of adaptive responses. To define the GSR regulatory components, we employed a yeast-one-hybrid assay to identify the protein(s) binding to the previously established functional GSR motif, termed the rapid stress response element (RSRE). This led to the isolation of octadecanoid-responsive AP2/ERF-domain transcription factor 47 (ORA47), a methyl jasmonate inducible protein. Subsequently, ORA47 transcriptional activity was confirmed using the RSRE-driven luciferase (LUC) activity assay performed in the ORA47 loss- and gain-of-function lines introgressed into the 4xRSRE::Luc background. In addition, the prime contribution of CALMODULIN-BINDING TRANSCRIPTIONAL ACTIVATOR3 (CAMTA3) protein in the induction of RSRE was reaffirmed by genetic studies. Moreover, exogenous application of methyl jasmonate led to enhanced levels of ORA47 and CAMTA3 transcripts, as well as the induction of RSRE::LUC activity. Metabolic analyses illustrated the reciprocal functional inputs of ORA47 and CAMTA3 in increasing JA levels. Lastly, transient assays identified JASMONATE ZIM-domain1 (JAZ1) as a repressor of RSRE::LUC activity. Collectively, the present study provides fresh insight into the initial features of the mechanism that transduces informational signals into adaptive responses. This mechanism involves the functional interplay between the JA biosynthesis/signaling cascade and the transcriptional reprogramming that potentiates GSR. Furthermore, these findings offer a window into the role of intraorganellar communication in the establishment of adaptive responses.

A single-cell Arabidopsis root atlas reveals developmental trajectories in wild-type and cell identity mutants

In all multicellular organisms, transcriptional networks orchestrate organ development. The Arabidopsis root, with its simple structure and indeterminate growth, is an ideal model for investigating the spatiotemporal transcriptional signatures underlying developmental trajectories. To map gene expression dynamics across root cell types and developmental time, we built a comprehensive, organ-scale atlas at single-cell resolution. In addition to estimating developmental progressions in pseudotime, we employed the mathematical concept of optimal transport to infer developmental trajectories and identify their underlying regulators. To demonstrate the utility of the atlas to interpret new datasets, we profiled mutants for two key transcriptional regulators at single-cell resolution, shortroot and scarecrow. We report transcriptomic and in vivo evidence for tissue trans-differentiation underlying a mixed cell identity phenotype in scarecrow. Our results support the atlas as a rich community resource for unraveling the transcriptional programs that specify and maintain cell identity to regulate spatiotemporal organ development.

A single-cell Arabidopsis root atlas reveals developmental trajectories in wild-type and cell identity mutants

In all multicellular organisms, transcriptional networks orchestrate organ development. The Arabidopsis root, with its simple structure and indeterminate growth, is an ideal model for investigating the spatiotemporal transcriptional signatures underlying developmental trajectories. To map gene expression dynamics across root cell types and developmental time, we built a comprehensive, organ-scale atlas at single-cell resolution. In addition to estimating developmental progressions in pseudotime, we employed the mathematical concept of optimal transport to infer developmental trajectories and identify their underlying regulators. To demonstrate the utility of the atlas to interpret new datasets, we profiled mutants for two key transcriptional regulators at single-cell resolution, shortroot and scarecrow. We report transcriptomic and in vivo evidence for tissue trans-differentiation underlying a mixed cell identity phenotype in scarecrow. Our results support the atlas as a rich community resource for unraveling the transcriptional programs that specify and maintain cell identity to regulate spatiotemporal organ development.

Cis-regulatory sequences in plants: Their importance, discovery, and future challenges

The identification and characterization of cis-regulatory DNA sequences and how they function to coordinate responses to developmental and environmental cues is of paramount importance to plant biology. Key to these regulatory processes are cis-regulatory modules (CRMs), which include enhancers and silencers. Despite the extraordinary advances in high-quality sequence assemblies and genome annotations, the identification and understanding of CRMs, and how they regulate gene expression, lag significantly behind. This is especially true for their distinguishing characteristics and activity states. Here, we review the current knowledge on CRMs and breakthrough technologies enabling identification, characterization, and validation of CRMs; we compare the genomic distributions of CRMs with respect to their target genes between different plant species, and discuss the role of transposable elements harboring CRMs in the evolution of gene expression. This is an exciting time to study cis-regulomes in plants; however, significant existing challenges need to be overcome to fully understand and appreciate the role of CRMs in plant biology and in crop improvement.

Autophagy during drought: function, regulation, and potential application

Drought is a major challenge for agricultural production since it causes substantial yield reduction and economic loss. Autophagy is a subcellular degradation and recycling pathway that functions in plant development and responses to many stresses, including drought. In this review, we summarize the current understanding of the function of autophagy and how autophagy is upregulated during drought stress. Autophagy helps plants to survive drought stress, and the mechanistic basis for this is beginning to be elucidated. Autophagy can selectively degrade aquaporins to adjust water permeability, and also degrades excess heme and damaged proteins to reduce their toxicity. In addition, autophagy can degrade regulators or components of hormone signaling pathways to promote stress responses. During drought recovery, autophagy degrades drought-induced proteins to reset the cell status. Autophagy is activated by multiple mechanisms during drought stress. Several transcription factors are induced by drought to upregulate autophagy-related gene expression, and autophagy is also regulated post-translationally through protein modification and stability. Based on these observations, manipulation of autophagy activity may be a promising approach for conferring drought tolerance in plants.

Multi-omics network-based functional annotation of unknown Arabidopsis genes

Unraveling gene function is pivotal to understanding the signaling cascades that control plant development and stress responses. As experimental profiling is costly and labor intensive, there is a clear need for high-confidence computational annotation. In contrast to detailed gene-specific functional information, transcriptomics data are widely available for both model and crop species. Here, we describe a novel automated function prediction method, which leverages complementary information from multiple expression datasets by analyzing study-specific gene co-expression networks. First, we benchmarked the prediction performance on recently characterized Arabidopsis thaliana genes, and showed that our method outperforms state-of-the-art expression-based approaches. Next, we predicted biological process annotations for known (n = 15 790) and unknown (n = 11 865) genes in A. thaliana and validated our predictions using experimental protein-DNA and protein-protein interaction data (covering >220 000 interactions in total), obtaining a set of high-confidence functional annotations. Our method assigned at least one validated annotation to 5054 (42.6%) unknown genes, and at least one novel validated function to 3408 (53.0%) genes with computational annotations only. These omics-supported functional annotations shed light on a variety of developmental processes and molecular responses, such as flower and root development, defense responses to fungi and bacteria, and phytohormone signaling, and help fill the information gap on biological process annotations in Arabidopsis. An in-depth analysis of two context-specific networks, modeling seed development and response to water deprivation, shows how previously uncharacterized genes function within the respective networks. Moreover, our automated function prediction approach can be applied in future studies to facilitate gene discovery for crop improvement.

A genome-scale TF-DNA interaction network of transcriptional regulation of Arabidopsis primary and specialized metabolism

Plant metabolism is more complex relative to individual microbes. In single-celled microbes, transcriptional regulation by single transcription factors (TFs) is sufficient to shift primary metabolism. Corresponding genome-level transcriptional regulatory maps of metabolism reveal the underlying design principles responsible for these shifts as a model in which master regulators largely coordinate specific metabolic pathways. Plant primary and specialized metabolism occur within innumerable cell types, and their reactions shift depending on internal and external cues. Given the importance of plants and their metabolites in providing humanity with food, fiber, and medicine, we set out to develop a genome-scale transcriptional regulatory map of Arabidopsis metabolic genes. A comprehensive set of protein-DNA interactions between Arabidopsis thaliana TFs and gene promoters in primary and specialized metabolic pathways were mapped. To demonstrate the utility of this resource, we identified and functionally validated regulators of the tricarboxylic acid (TCA) cycle. The resulting network suggests that plant metabolic design principles are distinct from those of microbes. Instead, metabolism appears to be transcriptionally coordinated via developmental- and stress-conditional processes that can coordinate across primary and specialized metabolism. These data represent the most comprehensive resource of interactions between TFs and metabolic genes in plants.

Parasitic modulation of host development by ubiquitin-independent protein degradation

Certain obligate parasites induce complex and substantial phenotypic changes in their hosts in ways that favor their transmission to other trophic levels. However, the mechanisms underlying these changes remain largely unknown. Here we demonstrate how SAP05 protein effectors from insect-vectored plant pathogenic phytoplasmas take control of several plant developmental processes. These effectors simultaneously prolong the host lifespan and induce witches' broom-like proliferations of leaf and sterile shoots, organs colonized by phytoplasmas and vectors. SAP05 acts by mediating the concurrent degradation of SPL and GATA developmental regulators via a process that relies on hijacking the plant ubiquitin receptor RPN10 independent of substrate ubiquitination. RPN10 is highly conserved among eukaryotes, but SAP05 does not bind insect vector RPN10. A two-amino-acid substitution within plant RPN10 generates a functional variant that is resistant to SAP05 activities. Therefore, one effector protein enables obligate parasitic phytoplasmas to induce a plethora of developmental phenotypes in their hosts.

Parasitic modulation of host development by ubiquitin-independent protein degradation

Certain obligate parasites induce complex and substantial phenotypic changes in their hosts in ways that favor their transmission to other trophic levels. However, the mechanisms underlying these changes remain largely unknown. Here we demonstrate how SAP05 protein effectors from insect-vectored plant pathogenic phytoplasmas take control of several plant developmental processes. These effectors simultaneously prolong the host lifespan and induce witches' broom-like proliferations of leaf and sterile shoots, organs colonized by phytoplasmas and vectors. SAP05 acts by mediating the concurrent degradation of SPL and GATA developmental regulators via a process that relies on hijacking the plant ubiquitin receptor RPN10 independent of substrate ubiquitination. RPN10 is highly conserved among eukaryotes, but SAP05 does not bind insect vector RPN10. A two-amino-acid substitution within plant RPN10 generates a functional variant that is resistant to SAP05 activities. Therefore, one effector protein enables obligate parasitic phytoplasmas to induce a plethora of developmental phenotypes in their hosts.

Genome-wide Analysis of Basic Helix-Loop-Helix Family Genes and Expression Analysis in Response to Drought and Salt Stresses in Hibiscus hamabo Sieb. et Zucc

The basic helix-loop-helix (bHLH) family of transcription factors is one of the most significant and biggest in plants. It is involved in the regulation of both growth and development, as well as stress response. Numerous members of the bHLH family have been found and characterized in woody plants in recent years. However, no systematic study of the bHLH gene family has been published for Hibiscus hamabo Sieb. et Zucc. In this research, we identified 162 bHLH proteins (HhbHLHs) from the genomic and transcriptomic datasets of H. hamabo, which were phylogenetically divided into 19 subfamilies. According to a gene structural study, the number of exon-introns in HhbHLHs varied between zero and seventeen. MEME research revealed that the majority of HhbHLH proteins contained three conserved motifs, 1, 4, and 5. The examination of promoter cis-elements revealed that the majority of HhbHLH genes had several cis-elements involved in plant growth and development and abiotic stress responses. In addition, the overexpression of HhbHLH2 increased salt and drought stress tolerance in Arabidopsis.

Time of the day prioritizes the pool of translating mRNAs in response to heat stress

The circadian clock helps organisms to anticipate and coordinate gene regulatory responses to changes in environmental stimuli. Under growth limiting temperatures, the time of the day modulates the accumulation of polyadenylated mRNAs. In response to heat stress, plants will conserve energy and selectively translate mRNAs. How the clock and/or the time of the day regulates polyadenylated mRNAs bound by ribosomes in response to heat stress is unknown. In-depth analysis of Arabidopsis thaliana translating mRNAs found that the time of the day gates the response of approximately one-third of the circadian-regulated heat-responsive translatome. Specifically, the time of the day and heat stress interact to prioritize the pool of mRNAs in cue to be translated. For a subset of mRNAs, we observed a stronger gated response during the day, and preferentially before the peak of expression. We propose previously overlooked transcription factors (TFs) as regulatory nodes and show that the clock plays a role in the temperature response for select TFs. When the stress was removed, the redefined priorities for translation recovered within 1 h, though slower recovery was observed for abiotic stress regulators. Through hierarchical network connections between clock genes and prioritized TFs, our work provides a framework to target key nodes underlying heat stress tolerance throughout the day.

Senescence-Associated Glycine max (Gm)NAC Genes: Integration of Natural and Stress-Induced Leaf Senescence

Leaf senescence is a genetically regulated developmental process that can be triggered by a variety of internal and external signals, including hormones and environmental stimuli. Among the senescence-associated genes controlling leaf senescence, the transcriptional factors (TFs) comprise a functional class that is highly active at the onset and during the progression of leaf senescence. The plant-specific NAC (NAM, ATAF, and CUC) TFs are essential for controlling leaf senescence. Several members of Arabidopsis AtNAC-SAGs are well characterized as players in elucidated regulatory networks. However, only a few soybean members of this class display well-known functions; knowledge about their regulatory circuits is still rudimentary. Here, we describe the expression profile of soybean GmNAC-SAGs upregulated by natural senescence and their functional correlation with putative AtNAC-SAGs orthologs. The mechanisms and the regulatory gene networks underlying GmNAC081- and GmNAC030-positive regulation in leaf senescence are discussed. Furthermore, new insights into the role of GmNAC065 as a negative senescence regulator are presented, demonstrating extraordinary functional conservation with the Arabidopsis counterpart. Finally, we describe a regulatory circuit which integrates a stress-induced cell death program with developmental leaf senescence via the NRP-NAC-VPE signaling module.

AtWAKL10, a Cell Wall Associated Receptor-Like Kinase, Negatively Regulates Leaf Senescence in Arabidopsis thaliana

Receptor-like kinases (RLKs) constitute a large group of cell surface receptors that play crucial roles in multiple biological processes. However, the function of most RLKs in plants has not been extensively explored, and much less for the class of cell wall associated kinases (WAKs) and WAK-like kinases (WAKLs). In this study, analyses of developmental expression patterns uncovered a putative role of AtWAKL10 in modulating leaf senescence, which was further investigated at physiological and molecular levels. The expression level of AtWAKL10 increased with the developmental progression and was rapidly upregulated in senescing leaf tissues. The promoter of AtWAKL10 contains various defense and hormone responsive elements, and its expression could be significantly induced by exogenous ABA, JA and SA. Moreover, the loss-of-function atwakl10 mutant showed earlier senescence along the course of natural development and accelerated leaf senescence under darkness and hormonal stresses, while plants overexpressing AtWAKL10 showed an opposite trend. Additionally, some defense and senescence related WRKY transcription factors could bind to the promoter of AtWAKL10. In addition, deletion and overexpression of AtWAKL10 caused several specific transcriptional alterations, including genes involved in cell extension, cell wall modification, defense response and senescence related WRKYs, which may be implicated in regulatory mechanisms adopted by AtWAKL10 in controlling leaf senescence. Taken together, these results revealed that AtWAKL10 negatively regulated leaf senescence.

A temporal hierarchy underpins the transcription factor-DNA interactome of the maize UPR

Adverse environmental conditions reduce crop productivity and often increase the load of unfolded or misfolded proteins in the endoplasmic reticulum (ER). This potentially lethal condition, known as ER stress, is buffered by the unfolded protein response (UPR), a set of signaling pathways designed to either recover ER functionality or ignite programmed cell death. Despite the biological significance of the UPR to the life of the organism, the regulatory transcriptional landscape underpinning ER stress management is largely unmapped, especially in crops. To fill this significant knowledge gap, we performed a large-scale systems-level analysis of the protein-DNA interaction (PDI) network in maize (Zea mays). Using 23 promoter fragments of six UPR marker genes in a high-throughput enhanced yeast one-hybrid assay, we identified a highly interconnected network of 262 transcription factors (TFs) associated with significant biological traits and 831 PDIs underlying the UPR. We established a temporal hierarchy of TF binding to gene promoters within the same family as well as across different families of TFs. Cistrome analysis revealed the dynamic activities of a variety of cis-regulatory elements (CREs) in ER stress-responsive gene promoters. By integrating the cistrome results into a TF network analysis, we mapped a subnetwork of TFs associated with a CRE that may contribute to UPR management. Finally, we validated the role of a predicted network hub gene using the Arabidopsis system. The PDIs, TF networks, and CREs identified in our work are foundational resources for understanding transcription-regulatory mechanisms in the stress responses and crop improvement.

A Gas-and-Brake Mechanism of bHLH Proteins Modulates Shade Avoidance

Plants detect proximity of competitors through reduction in the ratio between red and far-red light that triggers the shade avoidance syndrome, inducing responses such as accelerated shoot elongation and early flowering. Shade avoidance is regulated by PHYTOCHROME INTERACTING FACTORs, a group of basic helix-loop-helix (bHLH) transcription factors. Another (b)HLH protein, KIDARI (KDR), which is non-DNA-binding, was identified in de-etiolation studies and proposed to interact with LONG HYPOCOTYL IN FAR-RED1 (HFR1), a (b)HLH protein that inhibits shade avoidance. Here, we established roles of KDR in regulating shade avoidance in Arabidopsis (Arabidopsis thaliana) and investigated how KDR regulates the shade avoidance network. We showed that KDR is a positive regulator of shade avoidance and interacts with several negative growth regulators. We identified KDR interactors using a combination of yeast two-hybrid screening and dedicated confirmations with bimolecular fluorescence complementation. We demonstrated that KDR is translocated primarily to the nucleus when coexpressed with these interactors. A genetic approach confirmed that several of these interactions play a functional role in shade avoidance; however, we propose that KDR does not interact with HFR1 to regulate shade avoidance. Based on these observations, we propose that shade avoidance is regulated by a three-layered gas-and-brake mechanism of bHLH protein interactions, adding a layer of complexity to what was previously known.

A bipartite transcription factor module controlling expression in the bundle sheath of Arabidopsis thaliana

C₄ photosynthesis evolved repeatedly from the ancestral C₃ state, improving photosynthetic efficiency by ~50%. In most C₄ lineages, photosynthesis is compartmented between mesophyll and bundle sheath cells, but how gene expression is restricted to these cell types is poorly understood. Using the C₃ model Arabidopsis thaliana, we identified cis-elements and transcription factors driving expression in bundle sheath strands. Upstream of the bundle sheath preferentially expressed MYB76 gene, we identified a region necessary and sufficient for expression containing two cis-elements associated with the MYC and MYB families of transcription factors. MYB76 expression is reduced in mutant alleles for these transcription factors. Moreover, downregulated genes shared by both mutants are preferentially expressed in the bundle sheath. Our findings are broadly relevant for understanding the spatial patterning of gene expression, provide specific insights into mechanisms associated with the evolution of C₄ photosynthesis and identify a short tuneable sequence for manipulating gene expression in the bundle sheath.

Network-based approaches for understanding gene regulation and function in plants

Expression reprogramming directed by transcription factors is a primary gene regulation underlying most aspects of the biology of any organism. Our views of how gene regulation is coordinated are dramatically changing thanks to the advent and constant improvement of high-throughput profiling and transcriptional network inference methods: from activities of individual genes to functional interactions across genes. These technical and analytical advances can reveal the topology of transcriptional networks in which hundreds of genes are hierarchically regulated by multiple transcription factors at systems level. Here we review the state of the art of experimental and computational methods used in plant biology research to obtain large-scale datasets and model transcriptional networks. Examples of direct use of these network models and perspectives on their limitations and future directions are also discussed.

Transient Gene Expression is an Effective Experimental Tool for the Research into the Fine Mechanisms of Plant Gene Function: Advantages, Limitations, and Solutions

A large data array on plant gene expression accumulated thanks to comparative omic studies directs the efforts of researchers to the specific or fine effects of the target gene functions and, as a consequence, elaboration of relatively simple and concurrently effective approaches allowing for the insight into the physiological role of gene products. Numerous studies have convincingly demonstrated the efficacy of transient expression strategy for characterization of the plant gene functions. The review goals are (i) to consider the advantages and limitations of different plant systems and methods of transient expression used to find out the role of gene products; (ii) to summarize the current data on the use of the transient expression approaches for the insight into fine mechanisms underlying the gene function; and (iii) to outline the accomplishments in efficient transient expression of plant genes. In general, the review discusses the main and critical steps in each of the methods of transient gene expression in plants; areas of their application; main results obtained using plant objects; their contribution to our knowledge about the fine mechanisms of the plant gene functions underlying plant growth and development; and clarification of the mechanisms regulating complex metabolic pathways.

A Molecular Signal Integration Network Underpinning Arabidopsis Seed Germination

Seed dormancy is an adaptive trait defining where and when plants are established. Diverse signals from the environment are used to decide when to initiate seed germination, a process driven by the expansion of cells within the embryo. How these signals are integrated and transduced into the biomechanical changes that drive embryo growth remains poorly understood. Using Arabidopsis seeds, we demonstrate that cell-wall-loosening EXPANSIN (EXPA) genes promote gibberellic acid (GA)-mediated germination, identifying EXPAs as downstream molecular targets of this developmental phase transition. Molecular interaction screening identified transcription factors (TFs) that bind to both EXPA promoter fragments and DELLA GA-response regulators. A subset of these TFs is targeted each by nitric oxide (NO) and the phytochrome-interacting TF PIL5. This molecular interaction network therefore directly links the perception of an external environmental signal (light) and internal hormonal signals (GA and NO) with downstream germination-driving EXPA gene expression. Experimental validation of this network established that many of these TFs mediate GA-regulated germination, including TCP14/15, RAP2.2/2.3/2.12, and ZML1. The reduced germination phenotype of the tcp14 tcp15 mutant seed was partially rescued through ectopic expression of their direct target EXPA9. The GA-mediated control of germination by TCP14/15 is regulated through EXPA-mediated control of cell wall loosening, providing a mechanistic explanation for this phenotype and a previously undescribed role for TCPs in the control of cell expansion. This network reveals the paths of signal integration that culminate in seed germination and provides a resource to uncover links between the genetic and biomechanical bases of plant growth.

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The network linking integration of environmental signals to seed growth is mapped

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EXPANSIN gene expression is redundantly regulated and promotes GA-mediated germination

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The TCP14 transcription factor directly regulates EXPANSIN9 expression

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The tcp14/15 germination phenotype is complemented by EXPANSIN9 expression

FRS7 and FRS12 recruit NINJA to regulate expression of glucosinolate biosynthesis genes

The sessile lifestyle of plants requires accurate physiology adjustments to be able to thrive in a changing environment. Plants integrate environmental timing signals to control developmental and stress responses. Here, we identified Far1 Related Sequence (FRS) 7 and FRS12, two transcriptional repressors that accumulate in short-day conditions, as regulators of Arabidopsis glucosinolate (GSL) biosynthesis. Loss of function of FRS7 and FRS12 results in plants with increased amplitudes of diurnal expression of GSL pathway genes. Protein interaction analyses revealed that FRS7 and FRS12 recruit the NOVEL INTERACTOR OF JAZ (NINJA) to assemble a transcriptional repressor complex. Genetic and molecular evidence demonstrated that FRS7, FRS12 and NINJA jointly regulate the expression of GSL biosynthetic genes, and thus constitute a molecular mechanism that modulates specialized metabolite accumulation.

Extensive signal integration by the phytohormone protein network

Plant hormones coordinate responses to environmental cues with developmental programs¹, and are fundamental for stress resilience and agronomic yield². The core signalling pathways underlying the effects of phytohormones have been elucidated by genetic screens and hypothesis-driven approaches, and extended by interactome studies of select pathways³. However, fundamental questions remain about how information from different pathways is integrated. Genetically, most phenotypes seem to be regulated by several hormones, but transcriptional profiling suggests that hormones trigger largely exclusive transcriptional programs⁴. We hypothesized that protein-protein interactions have an important role in phytohormone signal integration. Here, we experimentally generated a systems-level map of the Arabidopsis phytohormone signalling network, consisting of more than 2,000 binary protein-protein interactions. In the highly interconnected network, we identify pathway communities and hundreds of previously unknown pathway contacts that represent potential points of crosstalk. Functional validation of candidates in seven hormone pathways reveals new functions for 74% of tested proteins in 84% of candidate interactions, and indicates that a large majority of signalling proteins function pleiotropically in several pathways. Moreover, we identify several hundred largely small-molecule-dependent interactions of hormone receptors. Comparison with previous reports suggests that noncanonical and nontranscription-mediated receptor signalling is more common than hitherto appreciated.