Glucose and auxin signaling interaction in controlling Arabidopsis thaliana seedlings root growth and development

Unveiling the impact of microplastics and nanoplastics on vascular plants: A cellular metabolomic and transcriptomic review

With increasing plastic manufacture and consumption, microplastics/nanoplastics (MP/NP) pollution has become one of the world's pressing global environmental issues, which poses significant threats to ecosystems and human health. In recent years, sharp increasing researches have confirmed that MP/NP had direct or indirect effects on vegetative growth and sexual process of vascular plant. But the potential mechanisms remain ambiguous. MP/NP particles can be adsorbed and/or absorbed by plant roots or leaves and thus cause diverse effects on plant. This holistic review aims to discuss the direct effects of MP/NP on vascular plant, with special emphasis on the changes of metabolic and molecular levels. MP/NP can alter substance and energy metabolism, as well as shifts in gene expression patterns. Key aspects affected by MP/NP stress include carbon and nitrogen metabolism, amino acids biosynthesis and plant hormone signal transduction, expression of stress related genes, carbon and nitrogen metabolism related genes, as well as those involved in pathogen defense. Additionally, the review provides updated insights into the growth and physiological responses of plants exposed to MP/NP, encompassing phenomena such as seed/spore germination, photosynthesis, oxidative stress, cytotoxicity, and genotoxicity. By examining the direct impact of MP/NP from both physiological and molecular perspectives, this review sets the stage for future investigations into the complex interactions between plants and plastic pollutants.

MORF9-dependent specific plastid RNA editing inhibits root growth under sugar starvation in Arabidopsis

Multiple organellar RNA editing factor (MORF) complex was shown to be highly associated with C-to-U RNA editing of vascular plant editosome. However, mechanisms by which MORF9-dependent plastid RNA editing controls plant development and responses to environmental alteration remain obscure. In this study, we found that loss of MORF9 function impaired PSII efficiency, NDH activity, and carbohydrate production, rapidly promoted nuclear gene expression including sucrose transporter and sugar/energy responsive genes, and attenuated root growth under sugar starvation conditions. Sugar repletion increased MORF9 and MORF2 expression in wild-type seedlings and reduced RNA editing of matK-706, accD-794, ndhD-383 and ndhF-290 in the morf9 mutant. RNA editing efficiency of ndhD-383 and ndhF-290 sites was diminished in the gin2/morf9 double mutants, and that of matK-706, accD-794, ndhD-383 and ndhF-290 sites were significantly diminished in the snrk1/morf9 double mutants. In contrast, overexpressing HXK1 or SnRK1 promoted RNA editing rate of matK-706, accD-794, ndhD-383 and ndhF-290 in leaves of morf9 mutants, suggesting that HXK1 partially impacts MORF9 mediated ndhD-383 and ndhF-290 editing, while SnRK1 may only affect MORF9-mediated ndhF-290 site editing. Collectively, these findings suggest that sugar and/or its intermediary metabolites impair MORF9-dependent plastid RNA editing resulting in derangements of plant root development.

Effects of water and exogenous glucose on apple seedling growth and soil enzyme activity in semiarid area

BACKGROUND

Soil water and organic carbon (C) are key factors affecting the growth and development of apple seedlings. The objective of the study was to investigate the effects of different soil moisture and glucose supplies on apple seedling growth and soil enzyme activities. We hypothesized that the growth of apple seedlings was affected by soil water and C content through their effects on root structure, plant physiological properties and soil enzymatic activities. A pot experiment consisting of nine treatments was set up, including three water treatments with soil moisture contents at 75-85% (normal irrigation, CK), 65-75% (light water stress, LS), and 55-65% (mild water stress, MS) of the soil field capacity, in combination with three glucose treatments with carbon/nitrogen (C/N) ratio of 7.5 (C1, no adding glucose), 10 (C2) and 15 (C3), respectively.

RESULTS

Results showed that the LSC2 treatment significantly increased plant height by 7%, stem diameter by 5% and leaf area by 17%, as compared with LSC1. Also, LSC2 significantly increased root dry weight, root vitality and soil enzyme activities. Moreover, results of leaf photosynthetic, malondialdehyde (MDA), peroxidase (POD), superoxide dismutase (SOD) and proline contents also proved that adding glucose improved the drought resistance of plants.

CONCLUSION

LSC2 treatment is more conducive to the growth of apple seedlings, and application of carbon has a good alleviation effect on plant water stress. The study demonstrated that addition of exogenous glucose alleviated light water deficiency, significantly affected root vitality, and promoted apple seedling growth. © 2024 Society of Chemical Industry.

Microcystin Contamination in Irrigation Water and Health Risk

Microcystins (MCs), natural hepatotoxic compounds produced by cyanobacteria, pose significant risks to water quality, ecosystem stability, and the well-being of animals, plants, and humans when present in elevated concentrations. The escalating contamination of irrigation water with MCs presents a growing threat to terrestrial plants. The customary practice of irrigating crops from local water sources, including lakes and ponds hosting cyanobacterial blooms, serves as a primary conduit for transferring these toxins. Due to their high chemical stability and low molecular weight, MCs have the potential to accumulate in various parts of plants, thereby increasing health hazards for consumers of agricultural products, which serve as the foundation of the Earth's food chain. MCs can bioaccumulate, migrate, potentially biodegrade, and pose health hazards to humans within terrestrial food systems. This study highlights that MCs from irrigation water reservoirs can bioaccumulate and come into contact with plants, transferring into the food chain. Additionally, it investigates the natural mechanisms that organisms employ for conjugation and the microbial processes involved in MC degradation. To gain a comprehensive understanding of the role of MCs in the terrestrial food chain and to elucidate the specific health risks associated with consuming crops irrigated with water contaminated with these toxins, further research is necessary.

Rhizosphere engineering for soil carbon sequestration

The rhizosphere is the central hotspot of water and nutrient uptake by plants, rhizodeposition, microbial activities, and plant-soil-microbial interactions. The plasticity of plants offers possibilities to engineer the rhizosphere to mitigate climate change. We define rhizosphere engineering as targeted manipulation of plants, soil, microorganisms, and management to shift rhizosphere processes for specific aims [e.g., carbon (C) sequestration]. The rhizosphere components can be engineered by agronomic, physical, chemical, biological, and genomic approaches. These approaches increase plant productivity with a special focus on C inputs belowground, increase microbial necromass production, protect organic compounds and necromass by aggregation, and decrease C losses. Finally, we outline multifunctional options for rhizosphere engineering: how to boost C sequestration, increase soil health, and mitigate global change effects.

Exploring the role of GhN/AINV23: implications for plant growth, development, and drought tolerance

BACKGROUND

Neutral/alkaline invertases (N/AINVs) play a crucial role in plant growth, development, and stress response, by irreversibly hydrolyzing sucrose into glucose and fructose. However, research on cotton in this area is limited. This study aims to investigate GhN/AINV23, a neutral/alkaline invertase in cotton, including its characteristics and biological functions.

RESULTS

In our study, we analyzed the sequence information, three-dimensional (3D) model, phylogenetic tree, and cis-elements of GhN/AINV23. The localization of GhN/AINV23 was determined to be in the cytoplasm and cell membrane. Quantitative real-time polymerase chain reaction (qRT-PCR) results showed that GhN/AINV23 expression was induced by abscisic acid (ABA), exogenous sucrose and low exogenous glucose, and inhibited by high exogenous glucose. In Arabidopsis, overexpression of GhN/AINV23 promoted vegetative phase change, root development, and drought tolerance. Additionally, the virus-induced gene silencing (VIGS) assay indicated that the inhibition of GhN/AINV23 expression made cotton more susceptible to drought stress, suggesting that GhN/AINV23 positively regulates plant drought tolerance.

CONCLUSION

Our research indicates that GhN/AINV23 plays a significant role in plant vegetative phase change, root development, and drought response. These findings provide a valuable foundation for utilizing GhN/AINV23 to improve cotton yield.

ZjHXK5 and ZjHXK6 negatively regulate the sugar metabolism of Ziziphus jujuba Mill

Hexokinase (HXK) plays a crucial role in plants, catalyzing the phosphorylation of hexose substances, which is one of the key steps in sugar metabolism and energy production. While HXK genes have been well-studied in model plants, the evolutionary and functional characteristics of HXK gene family in jujube is unknow. In this study, the HXK gene family members were identified by bioinformatics methods, the key members regulating glucose metabolism were identified by transcriptome data, and finally the function of the key genes was verified by instantaneous and stable genetic transformation. Our results showed that seven HXK genes were identified in the jujube genome, all of which were predict located in the chloroplast and contain Hexokinase-1 (PF00349) and Hexokinase-2 (PF03727) conserved domains. Most of HXK proteins were transmembrane protein with stable, lipid-soluble, hydrophilic. The secondary structure of ZjHXK proteins main α-helix, and contains two distinct tertiary structure. All ZjHXK genes contain nine exons and eight introns. Predictions of cis-regulatory elements indicate that the promoter region of ZjHXK contains a large number of MeJA responsive elements. Finally, combined with the analysis of the relationship between the expression and glucose metabolism, found that ZjHXK5 and ZjHXK6 may the key genes regulating sugar metabolism. Transient overexpression of ZjHXK5 and ZjHXK6 on jujube, or allogeneic overexpression of ZjHXK5 and ZjHXK6 on tomato would significantly reduce the content of total sugar and various sugar components. Transient silencing of ZjHXK5 and ZjHXK6 genes results in a significant increase in sucrose and total sugar content. Interestingly, the expression of ZjHXK5 and ZjHXK6 were also affected by methyl jasmonate.

Genetic regulation of lateral root development

Lateral roots (LRs) are an important part of plant root systems. In dicots, for example, after plants adapted from aquatic to terrestrial environments, filamentous pseudorhizae evolved to allow nutrient absorption. A typical plant root system comprises a primary root, LRs, root hairs, and a root cap. Classical plant roots exhibit geotropism (the tendency to grow downward into the ground) and can synthesize plant hormones and other essential substances. Root vascular bundles and complex spatial structures enable plants to absorb water and nutrients to meet their nutrient quotas and grow. The primary root carries out most functions during early growth stages but is later overtaken by LRs, underscoring the importance of LR development water and mineral uptake and the soil fixation capacity of the root. LR development is modulated by endogenous plant hormones and external environmental factors, and its underlying mechanisms have been dissected in great detail in Arabidopsis, thanks to its simple root anatomy and the ease of obtaining mutants. This review comprehensively and systematically summarizes past research (largely in Arabidopsis) on LR basic structure, development stages, and molecular mechanisms regulated by different factors, as well as future prospects in LR research, to provide broad background knowledge for root researchers.

Transcriptomic and Metabolomic Profiling Reveals the Variations in Carbohydrate Metabolism between Two Blueberry Cultivars

Blueberry is a high-quality fruit tree with significant nutritional and economic value, but the intricate mechanism of sugar accumulation in its fruit remains unclear. In this study, the ripe fruits of blueberry cultivars 'Anna' and 'Misty' were utilized as experimental materials, and physiological and multi-omics methodologies were applied to analyze the regulatory mechanisms of the difference in sugar content between them. The results demonstrated that the 'Anna' fruit was smaller and had less hardness than the 'Misty' fruit, as well as higher sugar content, antioxidant capability, and lower active substance content. A total of 7067 differentially expressed genes (DEGs) (3674 up-regulated and 3393 down-regulated) and 140 differentially abundant metabolites (DAMs) (82 up-regulated and 58 down-regulated) were identified between the fruits of the two cultivars. According to KEGG analysis, DEGs were primarily abundant in phenylpropanoid synthesis and hormone signal transduction pathways, whereas DAMs were primarily enriched in ascorbate and aldarate metabolism, phenylpropanoid biosynthesis, and the pentose phosphate pathway. A combined multi-omics study showed that 116 DEGs and 3 DAMs in starch and sucrose metabolism (48 DEGs and 1 DAM), glycolysis and gluconeogenesis (54 DEGs and 1 DAM), and the pentose phosphate pathway (14 DEGs and 1 DAM) were significantly enriched. These findings suggest that blueberries predominantly increase sugar accumulation by activating carbon metabolism network pathways. Moreover, we identified critical transcription factors linked to the sugar response. This study presents new understandings regarding the molecular mechanisms underlying blueberry sugar accumulation and will be helpful in improving blueberry fruit quality through breeding.

MYB6/bHLH13-AbSUS2 involved in sugar metabolism regulates root hair initiation of Abies beshanzuensis

Root hair is regarded as a pivotal complementary survival tactic for mycorrhizal plant like Abies beshanzuensis when symbiosis is disrupted. Relatively little is known about the mechanism underlying root hair morphogenesis in plant species that are strongly dependent on mycorrhizal symbiosis. Many of these species are endangered, and this knowledge is critical for ensuring their survival. Here, a MYB6/bHLH13-sucrose synthase 2 (AbSUS2) module was newly identified and characterized in A. beshanzuensis using bioinformatics, histochemistry, molecular biology, and transgenesis. Functional, expression pattern, and localization analysis showed that AbSUS2 participated in sucrose synthesis and was involved in root hair initiation in A. beshanzuensis. Additionally, the major enzymatic product of AbSUS2 was found to suppress root hair initiation in vitro. Our data further showed that a complex involving the transcription factors AbMYB6 and AbbHLH13 directly interacted with the promoter of AbSUS2 and strengthened its expression, thereby inhibiting root hair initiation in response to exogenous sucrose. Our findings offer novel insights into how root hair morphogenesis is regulated in mycorrhizal plants and also provide a new strategy for the preservation of endangered mycorrhizal plant species.

Leaf senescence attributes: the novel and emerging role of sugars as signaling molecules and the overlap of sugars and hormones signaling nodes

Sugars are the primary products of photosynthesis and play multiple roles in plants. Although sugars are usually considered to be the building blocks of energy storage and carbon transport molecules, they have also gradually come to be acknowledged as signaling molecules that can initiate senescence. Senescence is an active and essential process that occurs at the last developmental stage and corresponds to programmed degradation of: cells, tissues, organs, and entire organisms. It is a complex process involving: numerous biochemical changes, transporters, genes, and transcription factors. The process is controlled by multiple developmental signals, among which sugar signals are considered to play a vital role; however, the regulatory pathways involved are not fully understood. The dynamic mechanistic framework of sugar accumulation has an inconsistent effect on senescence through the sugar signaling pathway. Key metabolizing enzymes produce different sugar signals in response to the onset of senescence. Diverse sugar signal transduction pathways and a variety of sugar sensors are involved in controlling leaf senescence. This review highlights the processes underlying initiation of sugar signaling and crosstalk between sugars and hormones signal transduction pathways affecting leaf senescence. This summary of the state of current knowledge across different plants aids in filling knowledge gaps and raises key questions that remain to be answered with respect to regulation of leaf senescence by sugar signaling pathways.

Exogenous application of stevioside enhances root growth promotion in soybean (Glycine max (L.) Merrill)

The present study aims to investigate the impact of externally applied stevioside (a sugar-based glycoside) on soybean root growth by examining morpho-physiological characteristics, biochemical parameters, and gene expression. Soybean seedlings (10-day-old) were treated with stevioside (0, 8.0 μM, 24.5 μM, and 40.5 μM) for four times at six days' intervals by soil drenching. Treatment with 24.5 μM stevioside significantly increased root length (29.18 cm plant-1), root numbers (38.5 plant-1), root biomass (0.95 g plant-1 FW; 0.18 g plant-1 DW), shoot length (30.96 cm plant-1), and shoot biomass (2.14 g plant-1 FW; 0.36 g plant-1 DW) compared to the control. Moreover, 24.5 μM of stevioside was effective in enhancing photosynthetic pigments, leaf relative water content, and antioxidant enzymes compared to control. Conversely, plants exposed to a higher concentration of stevioside (40.5 μM), elevated total polyphenolic content, total flavonoid content, DPPH activity, total soluble sugars, reducing sugars, and proline content. Furthermore, gene expression of root growth development-related genes such as GmYUC2a, GmAUX2, GmPIN1A, GmABI5, GmPIF, GmSLR1, and GmLBD14 in stevioside-treated soybean plants were evaluated. Stevioside (8.0 μM) showed significant expression of GmPIN1A, whereas, 40.5 μM of stevioside enhanced GmABI5 expression. In contrast, most of the root growth development genes such as GmYUC2a, GmAUX2, GmPIF, GmSLR1, and GmLBD14, were highly expressed at 24.5 μM of stevioside treatment. Taken together, our results demonstrate the potential of stevioside in improving morpho-physiological traits, biochemical status, and the expression of root development genes in soybean. Hence, stevioside could be used as a supplement to enhance plant performance.

Ethylene-mediated metabolic priming increases photosynthesis and metabolism to enhance plant growth and stress tolerance

Enhancing crop yields is a major challenge because of an increasing human population, climate change, and reduction in arable land. Here, we demonstrate that long-lasting growth enhancement and increased stress tolerance occur by pretreatment of dark grown Arabidopsis seedlings with ethylene before transitioning into light. Plants treated this way had longer primary roots, more and longer lateral roots, and larger aerial tissue and were more tolerant to high temperature, salt, and recovery from hypoxia stress. We attributed the increase in plant growth and stress tolerance to ethylene-induced photosynthetic-derived sugars because ethylene pretreatment caused a 23% increase in carbon assimilation and increased the levels of glucose (266%), sucrose/trehalose (446%), and starch (87%). Metabolomic and transcriptomic analyses several days posttreatment showed a significant increase in metabolic processes and gene transcripts implicated in cell division, photosynthesis, and carbohydrate metabolism. Because of this large effect on metabolism, we term this "ethylene-mediated metabolic priming." Reducing photosynthesis with inhibitors or mutants prevented the growth enhancement, but this was partially rescued by exogenous sucrose, implicating sugars in this growth phenomenon. Additionally, ethylene pretreatment increased the levels of CINV1 and CINV2 encoding invertases that hydrolyze sucrose, and cinv1;cinv2 mutants did not respond to ethylene pretreatment with increased growth indicating increased sucrose breakdown is critical for this trait. A model is proposed where ethylene-mediated metabolic priming causes long-term increases in photosynthesis and carbohydrate utilization to increase growth. These responses may be part of the natural development of seedlings as they navigate through the soil to emerge into light.

Mining genes regulating root system architecture in maize based on data integration analysis

KEY MESSAGE

A new strategy that integrated multiple public data resources was established to construct root gene co-expression network and mine genes regulating root system architecture in maize. A root gene co-expression network, containing 13,874 genes, was constructed. A total of 53 root hub genes and 16 priority root candidate genes were identified. One priority root candidate was further functionally verified using overexpression transgenic maize lines. Root system architecture (RSA) is crucial for crops productivity and stress tolerance. In maize, few RSA genes are functionally cloned, and effective discovery of RSA genes remains a great of challenge. In this work, we established a strategy to mine maize RSA genes by integrating functionally characterized root genes, root transcriptome, weighted gene co-expression network analysis (WGCNA) and genome-wide association analysis (GWAS) of RSA traits based on public data resources. A total of 589 maize root genes were collected by searching well-characterized root genes in maize or homologous genes of other species. We performed WGCNA to construct a maize root gene co-expression network containing 13874 genes based on public available root transcriptome data, and further discovered the 53 hub genes related to root traits. In addition, by the prediction function of obtained root gene co-expression network, a total of 1082 new root candidate genes were explored. By further overlapping the obtained new root candidate gene with the root-related GWAS of RSA candidate genes, 16 priority root candidate genes were identified. Finally, a priority root candidate gene, Zm00001d023379 (encodes pyruvate kinase 2), was validated to modulate root open angle and shoot-borne roots number using its overexpression transgenic lines. Our results develop an integration analysis method for effectively exploring regulatory genes of RSA in maize and open a new avenue to mine the candidate genes underlying complex traits.

Photosynthetic sucrose drives the lateral root clock in Arabidopsis seedlings

The development of plant roots is subject to control by light. Here, we show that, similar to monotonous root elongation, the periodic induction of lateral roots (LRs) depends on the activation by light of photomorphogenic and photosynthetic photoreceptors in the shoot in a hierarchical order. The prevailing belief is that the plant hormone auxin serves as a mobile signal transmitter, responsible for interorgan communication, including light-controlled shoot-to-root connections. Alternatively, it has been proposed that the transcription factor HY5 assumes the role as a mobile shoot-to-root signal transmitter. Here, we provide evidence that photosynthetic sucrose produced in the shoot acts as the long-distance signal carrier regulating the local, tryptophan-based biosynthesis of auxin in the LR generation zone of the primary root tip, where the LR clock controls the pace of LR initiation in an auxin-tunable manner. Synchronization of LR formation with primary root elongation allows the adjustment of overall root growth to the photosynthetic performance of the shoot and the maintenance of a constant LR density during light-dark changes in a variable light environment.

Sucrose-induced auxin conjugate hydrolase restores symbiosis in a Medicago cytokinin perception mutant

Rhizobia-legume interactions recruit cytokinin for the induction of nodule primordia in the cortex. Cytokinin signaling regulates auxin transport and biosynthesis, causing local auxin accumulation, which triggers cortical cell division. Since sugar signaling can trigger auxin responses, we explored whether sugar treatments could rescue symbiosis in the Medicago truncatula cytokinin response 1 (cre1) mutant. Herein, we demonstrate that sucrose and its nonmetabolizable isomer turanose can trigger auxin response and recover functional symbiosis in cre1, indicating sucrose signaling to be necessary for the restoration of symbiosis. In both M. truncatula A17 (wild type) and cre1, sucrose signaling significantly upregulated IAA-Ala Resistant 3 (IAR33), encoding an auxin conjugate hydrolase, in rhizobia-infected as well as in uninfected roots. Knockdown of IAR33 (IAR33-KD) significantly reduced nodulation in A17, highlighting the importance of deconjugation-mediated auxin accumulation during nodule inception. In cre1, IAR33-KD restricted the sucrose-mediated restoration of functional symbiosis, suggesting that deconjugation-mediated auxin accumulation plays a key role in the absence of CRE1-mediated auxin biosynthesis and transport control. Overexpression of IAR33 also restored functional symbiosis in cre1, further suggesting that IAR33 mediates auxin accumulation in response to sucrose signaling. Since all the observed sucrose-mediated responses were common to A17 and cre1, deconjugation-mediated auxin response appeared to be independent of CRE1, which normally governs local auxin accumulation in the presence of rhizobia. We propose that sucrose-dependent restoration of symbiosis in cre1 occurs by the activation of IAR33-mediated auxin deconjugation.

Fine Tuning of ROS, Redox and Energy Regulatory Systems Associated with the Functions of Chloroplasts and Mitochondria in Plants under Heat Stress

Heat stress severely affects plant growth and crop production. It is therefore urgent to uncover the mechanisms underlying heat stress responses of plants and establish the strategies to enhance heat tolerance of crops. The chloroplasts and mitochondria are known to be highly sensitive to heat stress. Heat stress negatively impacts on the electron transport chains, leading to increased production of reactive oxygen species (ROS) that can cause damages on the chloroplasts and mitochondria. Disruptions of photosynthetic and respiratory metabolisms under heat stress also trigger increase in ROS and alterations in redox status in the chloroplasts and mitochondria. However, ROS and altered redox status in these organelles also activate important mechanisms that maintain functions of these organelles under heat stress, which include HSP-dependent pathways, ROS scavenging systems and retrograde signaling. To discuss heat responses associated with energy regulating organelles, we should not neglect the energy regulatory hub involving TARGET OF RAPAMYCIN (TOR) and SNF-RELATED PROTEIN KINASE 1 (SnRK1). Although roles of TOR and SnRK1 in the regulation of heat responses are still unknown, contributions of these proteins to the regulation of the functions of energy producing organelles implicate the possible involvement of this energy regulatory hub in heat acclimation of plants.

Phenotypic effect of growth media on Arabidopsis thaliana root hair growth

Over the years, many different growth media have been used to grow Arabidopsis thaliana in vitro in petri dishes. For these media the nutrient composition may vary, sugars may or may not be added, the medium may or may not be buffered and there is a choice between different gelling agents. The magnitude of possible combinations of these variables obstructs easy comparison of seedling phenotypes grown on the different media. This is especially obvious when it concerns the study of root hairs that are extremely sensitive to changes in their environment. To demonstrate this effect, we have grown Arabidopsis thaliana wild-type seeds on 18 different combinations of growth media and quantified root hair development. Comparison of root hair length and the respective root hair profiles identified the media that result in the formation of the longest root hairs. On these favored media they elongate through tip growth at a constant growth rate until they reach their final length (around 0.6 mm) at a distance of ±4 mm from the root tip.

Transcriptome analysis reveals that jasmonic acid biosynthesis and signaling is associated with the biosynthesis of asperosaponin VI in Dipsacus asperoides

Dipsacus asperoides is a perennial herb, the roots of which are abundant in asperosaponin VI, which has important medicinal value. However, the molecular mechanism underlying the biosynthesis of asperosaponin VI in D. asperoides remains unclear. In present study, a comprehensive investigation of asperosaponin VI biosynthesis was conducted at the levels of metabolite and transcript during root development. The content of asperosaponin VI was significantly accumulated in two-leaf stage roots, and the spatial distribution of asperosaponin VI was localized in the xylem. The concentration of asperosaponin VI gradually increased in the root with the development process. Transcriptome analysis revealed 3916 unique differentially expressed genes (DEGs) including 146 transcription factors (TFs) during root development in D. asperoides. In addition, α-linolenic acid metabolism, jasmonic acid (JA) biosynthesis, JA signal transduction, sesquiterpenoid and triterpenoid biosynthesis, and terpenoid backbone biosynthesis were prominently enriched. Furthermore, the concentration of JA gradually increased, and genes involved in α-linolenic acid metabolism, JA biosynthesis, and triterpenoid biosynthesis were up-regulated during root development. Moreover, the concentration of asperosaponin VI was increased following methyl jasmonate (MeJA) treatment by activating the expression of genes in the triterpenoid biosynthesis pathway, including acetyl-CoA acetyltransferase (DaAACT), 3-hydroxy-3-methylglutaryl coenzyme A synthase (DaHMGCS), 3-hydroxy-3-methylglutaryl coenzyme-A reductase (DaHMGCR). We speculate that JA biosynthesis and signaling regulates the expression of triterpenoid biosynthetic genes and facilitate the biosynthesis of asperosaponin VI. The results suggest a regulatory network wherein triterpenoids, JA, and TFs co-modulate the biosynthesis of asperosaponin VI in D. asperoides.

Metabolites from Bacillus subtilis J-15 Affect Seedling Growth of Arabidopsis thaliana and Cotton Plants

Bacillus subtilis J-15 is a plant growth-promoting rhizobacteria isolated from the soil rhizosphere of cotton and is resistant to cotton verticillium wilt. This study evaluated the effects of metabolites of J-15 (J-15-Ms), including mycosubtilin, on plant growth using Arabidopsis and cotton plants. The results showed that J-15-Ms promoted Arabidopsis seeding growth at lower concentrations of 0.2 μg/mL but inhibited the growth at higher concentrations, such as 20 μg/mL. Similar results were obtained in cotton. Thus, J-15-Ms-treated plants showed low-concentration-induced growth promotion and high-concentration-induced growth inhibition. The J-15-Ms components were analyzed by liquid chromatography-mass spectrometry. Correlation analysis using the J-15 genomic databases suggested that J-15 may synthesize indoleacetic acid via the indole-3-pymvate pathway and indole-3-acetamide pathway. Treatment with mycosubtilin, a purified peptide from J-15-Ms, showed that the peptide promoted Arabidopsis growth at a low concentration (0.1 μg/mL) and inhibited plant growth at high concentrations (higher than 1 μg/mL), which also significantly increased plant lateral root number. Transcriptomic analysis showed that mycosubtilin might promote lateral root development and inhibit plant primary root growth by regulating the expression of the plant hormone signaling pathway. This study reveals the mechanism of Bacillus subtilis J-15 in affecting plant growth.

A glucose-target of rapamycin signaling axis integrates environmental history of heat stress through maintenance of transcription-associated epigenetic memory in Arabidopsis

In nature, plants cope with adversity and have established strategies that recall past episodes and enable them to better cope with stress recurrences by establishing a 'stress memory'. Emerging evidence suggests that glucose (Glc) and target of rapamycin (TOR), central regulators of plant growth, have remarkable functions in stress adaptation. However, whether TOR modulates a stress memory response is so far unknown. Global transcriptome profiling identified that Glc, through TOR, regulates the expression of numerous genes involved in thermomemory. Priming of TOR overexpressors with mild heat showed better stress endurance, whereas TOR RNAi showed reduced thermomemory. This thermomemory is linked with histone methylation at specific sites of heat stress (HS) genes. TOR promotes long-term accumulation of H3K4me3 on thermomemory-associated gene promoters, even when transcription of those genes reverts to their basal level. Our results suggest that ARABIDOPSIS TRITHORAX 1 (ATX1), an H3K4 methyltransferase already shown to regulate H3K4me3 levels at the promoters of HS recovery genes, is a direct target of TOR signaling. The TOR-activating E2Fa binds to the promoter of ATX1 and regulates its expression, which ultimately regulates thermomemory. Collectively, our findings reveal a mechanistic framework in which Glc-TOR signaling determines the integration of stress and energy signaling to regulate thermomemory.

Long-distance transport of sucrose in source leaves promotes sink root growth by the EIN3-SUC2 module

In most plants, sucrose, a major storage sugar, is transported into sink organs to support their growth. This key physiological process is dependent on the function of sucrose transporters. Sucrose export from source tissues is predominantly controlled through the activity of SUCROSE TRANSPORTER 2 (SUC2), required for the loading of sucrose into the phloem of Arabidopsis plants. However, how SUC2 activity is controlled to support root growth remains unclear. Glucose is perceived via the function of HEXOKINASE 1 (HXK1), the only known nuclear glucose sensor. HXK1 negatively regulates the stability of ETHYLENE-INSENSITIVE3 (EIN3), a key ethylene/glucose interaction component. Here we show that HXK1 functions upstream of EIN3 in the regulation of root sink growth mediated by glucose signaling. Furthermore, the transcription factor EIN3 directly inhibits SUC2 activity by binding to the SUC2 promoter, regulating glucose signaling linked to root sink growth. We demonstrate that these molecular components form a HXK1-EIN3-SUC2 module integral to the control of root sink growth. Also, we demonstrate that with increasing age, the HXK1-EIN3-SUC2 module promotes sucrose phloem loading in source tissues thereby elevating sucrose levels in sink roots. As a result, glucose signaling mediated-sink root growth is facilitated. Our findings thus establish a direct molecular link between the HXK1-EIN3-SUC2 module, the source-to sink transport of sucrose and root growth.

In Arabidopsis and most crops, sucrose transporters are positioned in the vascular bundles of leaf blades where they have crucial roles in balancing source and sink activities. However, little molecular detail is currently available regarding the modulation of sucrose transporter activity. Here, we demonstrate that the transcriptional regulator, EIN3, functions downstream of HEXOKINASE 1 (HXK1), which acts upstream of SUC2 in the regulation of root sink growth mediated by glucose signaling. Further, EIN3 directly represses SUC2 function by negatively regulating SUC2 transcription. We further demonstrate that these components form the HXK1-EIN3-SUC2 module to facilitate sucrose phloem loading in source tissues thereby elevating sucrose content in sink roots.

Abscisic Acid Induces Adventitious Rooting in Cucumber (Cucumis sativus L.) by Enhancing Sugar Synthesis

Abscisic acid (ABA) affects many important plant processes, such as seed germination, root elongation and stomatal movement. However, little information is available about the relationship between ABA and sugar synthesis during adventitious root formation. The aim of this study was to evaluate the effect of ABA on adventitious root formation in cucumber and whether the effect of this plant hormone on sugar synthesis could be included as a causative factor for adventitious root development. We determined the contents of glucose, sucrose, starch, total sugar and sugar-related enzymes, including sucrose synthase (SS), sucrose phosphate synthase (SPS), hexokinase (HK) and pyruvate kinase (PK) activities in ABA treatment. We also quantified the relative expression of sucrose or glucose synthesis genes during this process. Increasing ABA concentrations significantly improved adventitious root formation, with the most considerable effect at 0.05 μM. Compared to the control, ABA treatment showed higher glucose, sucrose, starch and total sugar contents. Moreover, ABA treatment increased glucose-6-phosphate (G6P), fructose-6-phosphate (F6P) and glucose-1-phosphate (G1P) contents in cucumber explants during adventitious root development, which was followed by an increase of activities of sucrose-related enzymes SS and SPS, glucose-related enzymes HK and PK. ABA, meanwhile, upregulated the expression levels of sucrose or glucose synthesis-related genes, including CsSuSy1, CsSuSy6, CsHK1 and CsHK3. These results suggest that ABA may promote adventitious root development by increasing the contents of glucose, sucrose, starch, total sugar, G6P, F6P and G1P, the activities of SS, SPS, HK, SPS and the expression levels of CsSuSy1, CsSuSy6, CsHK1 and CsHK3 genes. These findings provide evidence for the physiological role of ABA during adventitious root formation and provide a new understanding of the possible relationship between ABA and sugar synthesis during adventitious rooting in plants.

Transcriptomic profiles of poplar (Populus simonii × P. nigra) cuttings during adventitious root formation

The formation of adventitious roots (ARs) is vital for the vegetative propagation of poplars. However, the relevant mechanisms remain unclear. To reveal the underlying molecular mechanism, we used RNA-seq to investigate the transcriptional alterations of poplar cuttings soaked in water for 0, 2, 4, 6, 8, and 10 d; 3,798 genes were differentially expressed at all the time points, including 2,448 upregulated and 1,350 downregulated genes. Biological processes including “cell cycle,” “photosynthesis,” “regulation of hormone levels,” and “auxin transport” were enriched in the differentially expressed genes (DEGs). KEGG results showed that the common DEGs were most enriched in the pathway of “Carbon fixation in photosynthetic organisms” and “Starch and sucrose metabolism.” We further dissected 38 DEGs related to root and auxin, including two lateral root primordium 1 (LRP1), one root meristem growth factor (RGF9), one auxin-induced in the root (AIR12), three rooting-associated genes (AUR1 and AUR3), eight auxin transcription factors (ARFs and LBDs), 10 auxin respective genes (SAURs and GH3s), nine auxin transporters (PINs, ABCs, LAX2, and AUXs), and four auxin signal genes (IAAs and TIR1). We found that the rooting abilities of poplar cuttings with and without leaves are different. By applying different concentrations of IBA and sucrose to the top of cuttings without leaves, we found that 0.2 mg/ml IBA and 2 mg/ml sucrose had the best effect on promoting AR formation. The transcriptome results indicated photosynthesis may influence AR formation in poplar cuttings with leaves and revealed a potential regulatory mechanism of leafy cuttage from poplar cuttings. In addition, we provided a new perspective to resolve rooting difficulties in recalcitrant species.

The interaction between exogenous IBA with sucrose, light and ventilation alters the expression of ARFs and Aux/IAA genes in Carica papaya plantlets

The interaction between exogenous IBA with sucrose, light and ventilation, alters the expression of ARFs and Aux/IAA genes in in vitro grown Carica papaya plantlets. In vitro papaya plantlets normally show low rooting percentages during their ex vitro establishment that eventually leads to high mortality when transferred to field conditions. Indole-3-butyric acid (IBA) auxin is normally added to culture medium, to achieve adventitious root formation on in vitro papaya plantlets. However, the molecular mechanisms occurring when IBA is added to the medium under varying external conditions of sugar, light and ventilation have not been studied. Auxin response factors (ARF) are auxin-transcription activators, while auxin/indole-3-acetic acid (Aux/IAA) are auxin-transcription repressors, that modulate key components involved in auxin signaling in plants. In the present study, we identified 12 CpARF and 18 CpAux/IAA sequences in the papaya genome. The cis-acting regulatory elements associated to those CpARFs and CpAux/IAA gene families were associated with stress and hormone responses. Furthermore, a comprehensive characterization and expression profiling analysis was performed on 6 genes involved in rhizogenesis formation (CpARF5, 6, 7 and CpAux/IAA11, 13, 14) from in vitro papaya plantlets exposed to different rhizogenesis-inducing treatments. In general, intact in vitro plantlets were not able to produce adventitious roots, when IBA (2 mg L^-1) was added to the culture medium; they became capable to produce roots and increased their ex-vitro survival. However, the best rooting and survival % were obtained when IBA was added in combination with adequate sucrose supply (20 g L^-1), increased light intensity (750 µmol photon m^-2 s^-1) and ventilation systems within the culture vessel. Interestingly, it was precisely under those conditions that promoted high rooting and survival %, where the highest expression of CpARFs, but the lowest expression of CpAux/IAAs occurred. One interesting case occurred when in vitro plantlets were exposed to high levels of light in the absence of added IBA, as high rooting and survival occurred, even though no exogenous auxin was added. In fact, plantlets from this treatment showed the right expression profile between auxin activators/repressors genes, in both stem base and root tissues.

Mutation of OsPIN1b by CRISPR/Cas9 Reveals a Role for Auxin Transport in Modulating Rice Architecture and Root Gravitropism

The distribution and content of auxin within plant tissues affect a variety of important growth and developmental processes. Polar auxin transport (PAT), mainly mediated by auxin influx and efflux transporters, plays a vital role in determining auxin maxima and gradients in plants. The auxin efflux carrier PIN-FORMED (PIN) family is one of the major protein families involved in PAT. Rice (Oryza sativa L.) genome possesses 12 OsPIN genes. However, the detailed functions of OsPIN genes involved in regulating the rice architecture and gravity response are less well understood. In the present study, OsPIN1b was disrupted by CRISPR/Cas9 technology, and its roles in modulating rice architecture and root gravitropism were investigated. Tissue-specific analysis showed that OsPIN1b was mainly expressed in roots, stems and sheaths at the seedling stage, and the transcript abundance was progressively decreased during the seedling stages. Expression of OsPIN1b could be quickly and greatly induced by NAA, indicating that OsPIN1b played a vital role in PAT. IAA homeostasis was disturbed in ospin1b mutants, as evidenced by the changed sensitivity of shoot and root to NAA and NPA treatment, respectively. Mutation of OsPIN1b resulted in pleiotropic phenotypes, including decreased growth of shoots and primary roots, reduced adventitious root number in rice seedlings, as well as shorter and narrower leaves, increased leaf angle, more tiller number and decreased plant height and panicle length at the late developmental stage. Moreover, ospin1b mutants displayed a curly root phenotype cultured with tap water regardless of lighting conditions, while nutrient solution culture could partially rescue the curly root phenotype in light and almost completely abolish this phenotype in darkness, indicating the involvement of the integration of light and nutrient signals in root gravitropism regulation. Additionally, amyloplast sedimentation was impaired in the peripheral tiers of the ospin1b root cap columella cell, while it was not the main contributor to the abnormal root gravitropism. These data suggest that OsPIN1b not only plays a vital role in regulating rice architecture but also functions in regulating root gravitropism by the integration of light and nutrient signals.

Root Foraging Strategy Improves the Adaptability of Tea Plants (Camellia sinensis L.) to Soil Potassium Heterogeneity

Root foraging enables plants to obtain more soil nutrients in a constantly changing nutrient environment. Little is known about the adaptation mechanism of adventitious roots of plants dominated by asexual reproduction (such as tea plants) to soil potassium heterogeneity. We investigated root foraging strategies for K by two tea plants (low-K tolerant genotype “1511” and low-K intolerant genotype “1601”) using a multi-layer split-root system. Root exudates, root architecture and transcriptional responses to K heterogeneity were analyzed by HPLC, WinRHIZO and RNA-seq. With the higher leaf K concentrations and K biological utilization indexes, “1511” acclimated to K heterogeneity better than “1601”. For “1511”, maximum total root length and fine root length proportion appeared on the K-enriched side; the solubilization of soil K reached the maximum on the low-K side, which was consistent with the amount of organic acids released through root exudation. The cellulose decomposition genes that were abundant on the K-enriched side may have promoted root proliferation for “1511”. This did not happen in “1601”. The low-K tolerant tea genotype “1511” was better at acclimating to K heterogeneity, which was due to a smart root foraging strategy: more roots (especially fine roots) were developed in the K-enriched side; more organic acids were secreted in the low-K side to activate soil K and the root proliferation in the K-enriched side might be due to cellulose decomposition. The present research provides a practical basis for a better understanding of the adaptation strategies of clonal woody plants to soil nutrient availability.

Roles of auxin in the inhibition of shoot branching in 'Dugan' fir

Shoot branching substantially impacts vegetative and reproductive growth as well as wood characteristics in perennial woody species by shaping the shoot system architecture. Although plant hormones have been shown to play a fundamental role in shoot branching in annual species, their corresponding actions in perennial woody plants are largely unknown, in part due to the lack of branching mutants. Here, we demonstrated the role of plant hormones in bud dormancy transition toward activation and outgrowth in woody plants by comparing the physiological and molecular changes in the apical shoot stems of 'Yangkou' 020 fir and 'Dugan' fir, two Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) clones with normal and completely abolished branching phenotypes, respectively. Our studies showed that the defect in bud outgrowth was the cause of failed shoot branching in 'Dugan' fir whereas apically derived signals acted as triggers of this ectopic bud activity. Further studies indicated that auxin played a key role in inhibiting bud outgrowth in 'Dugan' fir. During bud dormancy release, the differential auxin resistant 1/Like AUX1 (AUX1/LAX) and PIN-formed (PIN) activity resulted in an ectopic auxin/indole-3-acetic acid (IAA) accumulation in the apical shoot stem of 'Dugan' fir, which could inhibit the cell cycle in the axillary meristem by decreasing cytokinin (CK) biosynthesis but increasing abscisic acid (ABA) production and response through the signaling pathway. In contrast, during bud activation and outgrowth, the striking increase in auxin biosynthesis and PIN activity in the shoot tip of 'Dugan' fir may trigger the correlative inhibition of axillary buds by modulating the polar auxin transport stream (PATS) and connective auxin transport (CAT) in shoots, and by influencing the biosynthesis of secondary messengers, including CK, gibberellin (GA) and ABA, thereby inducing the paradormancy of axillary buds in 'Dugan' fir by apical dominance under favorable conditions. The findings of this study provide important insights into the roles of plant hormones in bud outgrowth control in perennial woody plants.

Roles of TOR signaling in nutrient deprivation and abiotic stress

In living organisms, nutrient, energy, and environmental stimuli sensing and signaling are considered as the most primordial regulatory networks governing growth and development. Target of Rapamycin (TOR) is a diversified Serine/Threonine protein kinase existing in all eukaryotes that regulates distinct salient growth and developmental signaling pathways. TOR signaling acts as a central hub in plants that allows a variety of nutrients, energy, hormones, and environmental stimuli to be integrated. TOR is activated by several nutrients and promotes energy-consuming processes such as cell division, protein translation, mRNA translation and ribosome biogenesis. We summarized the recent findings on the TOR function in regulating the dynamic networks of nutrients, including sugar, sulfur, nitrogen, carbon, phosphorus, potassium, and amino acids. TOR's role in abiotic stress was discussed, in which TOR orchestrating stress signaling, including heat, cold, salt, and osmotic stress, to regulate transcriptional and metabolic reprogramming, as well as growth and development. The interconnections between TOR and SnRK1 kinase were discussed in controlling nutrient deprivation and abiotic stress.

Alkaline α-galactosidase 2 (CsAGA2) plays a pivotal role in mediating source-sink communication in cucumber

Sugars are necessary for plant growth and fruit development. Cucumber (Cucumis sativus L.) transports sugars, mainly raffinose family oligosaccharides (RFOs), in the vascular bundle. As the dominant sugars in cucumber fruit, glucose and fructose are derived from sucrose, which is the product of RFO hydrolysis by α-galactosidase (α-Gal). Here, we characterized the cucumber alkaline α-galactosidase 2 (CsAGA2) gene and found that CsAGA2 has undergone human selection during cucumber domestication. Further experiments showed that the expression of CsAGA2 increases gradually during fruit development, especially in fruit vasculature. In CsAGA2-RNA interference (RNAi) lines, fruit growth was delayed because of lower hexose production in the peduncle and fruit main vascular bundle (MVB). In contrast, CsAGA2-overexpressing (OE) plants displayed bigger fruits. Functional enrichment analysis of transcriptional data indicated that genes related to sugar metabolism, cell wall metabolism, and hormone signaling were significantly downregulated in the peduncle and fruit MVBs of CsAGA2-RNAi plants. Moreover, downregulation of CsAGA2 also caused negative feedback regulation on source leaves, which was shown by reduced photosynthetic efficiency, fewer plasmodesmata at the surface between mesophyll cell and intermediary cell (IC) or between IC and sieve element, and downregulated gene expression and enzyme activities related to phloem loading, as well as decreased sugar production and exportation from leaves and petioles. The opposite trend was observed in CsAGA2-OE lines. Overall, we conclude that CsAGA2 is essential for cucumber fruit set and development through mediation of sugar communication between sink strength and source activity.

Review: Isoprenoid and aromatic cytokinins in shoot branching

Shoot branching is an important event of plant development that defines growth and reproduction. The BRANCHED1 gene (BRC1/TB1/FC1) is crucial for this process. Within the phytohormones, cytokinins directly activate axillary buds to promote shoot branching. In addition, strigolactones and auxins inhibit bud outgrowth. This review addresses the involvement of aromatic and isoprenoid cytokinins in shoot branching. And how auxins and strigolactones contribute to regulating this process also. The results obtained by others and our working group with lemongrass (Cymbopogon citratus) show that cytokinins affect both shoot and root apical meristem development, consistent with other plant species. However, many questions remain about how cytokinins and strigolactones antagonistically regulate BRC1 gene expression. Additionally, many details of the interaction among cytokinins, auxins, and strigolactones need to be clarified. We will gain a more comprehensive scheme of bud outgrowth with these details.

Jasmonic acid coordinates with light, glucose and auxin signalling in regulating branching angle of Arabidopsis lateral roots

The role of jasmonates (JAs) in primary root growth and development and in plant response to external stimuli is already known. However, its role in lateral root (LR) development remains to be explored. Our work identified methyl jasmonate (MeJA) as a key phytohormone in determining the branching angle of Arabidopsis LRs. MeJA inclines the LRs to a more vertical orientation, which was dependent on the canonical JAR1-COI1-MYC2,3,4 signalling. Our work also highlights the dual roles of light in governing LR angle. Light signalling enhances JA biosynthesis, leading to erect root architecture; whereas, glucose (Glc) induces wider branching angles. Combining physiological and molecular assays, we revealed that Glc antagonises the MeJA response via TARGET OF RAPAMYCIN (TOR) signalling. Moreover, physiological assays using auxin mutants, MYC2-mediated transcriptional activation of LAZY2, LAZY4 and auxin biosynthetic gene CYP79B2, and asymmetric distribution of DR5::GFP and PIN2::GFP pinpointed the role of an intact auxin machinery required by MeJA for vertical growth of LRs. We also demonstrated that light perception and signalling are indispensable for inducing vertical angles by MeJA. Thus, our investigation highlights antagonism between light and Glc signalling and how they interact with JA-auxin signals to optimise the branching angle of LRs.

An improved Raphanus sativus cv. WK10039 genome localizes centromeres, uncovers variation of DNA methylation and resolves arrangement of the ancestral Brassica genome blocks in radish chromosomes

This study presents an improved genome of Raphanus sativus cv. WK10039 uncovering centromeres and differentially methylated regions of radish chromosomes. Comprehensive genome comparison of radish and diploid Brassica species of U's triangle reveals that R. sativus arose from the Brassica B genome lineage and is a sibling species of B. nigra. Radish (Raphanus sativus L.) is a key root vegetable crop closely related to the Brassica crop species of the family Brassicaceae. We reported a draft genome of R. sativus cv. WK10039 (Rs1.0), which had 54.6 Mb gaps. To study the radish genome and explore previously unknown regions, we generated an improved genome assembly (Rs2.0) by long-read sequencing and high-resolution genome-wide mapping of chromatin interactions. Rs2.0 was 434.9 Mb in size with 0.27 Mb gaps, and the N50 scaffold length was 37.3 Mb (40-fold larger assembly compared to Rs1.0). Approximately 38% of Rs2.0 was comprised of repetitive sequences, and 52,768 protein-coding genes and 4845 non-protein-coding genes were predicted and annotated. The improved contiguity and coverage of Rs2.0, along with the detection of highly methylated regions, enabled localization of centromeres where R. sativus-specific centromere-associated repeats, full-length OTA and CRM LTR-Gypsy retrotransposons, hAT-Ac, CMC-EnSpm and Helitron DNA transposons, and sequences highly homologous to B. nigra centromere-specific CENH3-associated CL sequences were enriched. Whole-genome bisulfite sequencing combined with mRNA sequencing identified differential epigenetic marks in the radish genome related to tissue development. Synteny comparison and genomic distance analysis of radish and three diploid Brassica species of U's triangle suggested that the radish genome arose from the Brassica B genome lineage through unique rearrangement of the triplicated ancestral Brassica genome after splitting of the Brassica A/C and B genomes.

Sucrose Synthase and Fructokinase Are Required for Proper Meristematic and Vascular Development

Sucrose synthase (SuSy) and fructokinase (FRK) work together to control carbohydrate flux in sink tissues. SuSy cleaves sucrose into fructose and UDP-glucose; whereas FRK phosphorylates fructose. Previous results have shown that suppression of the SUS1,3&4 genes by SUS-RNAi alters auxin transport in the shoot apical meristems of tomato plants and affects cotyledons and leaf structure; whereas antisense suppression of FRK2 affects vascular development. To explore the joint developmental roles of SuSy and FRK, we crossed SUS-RNAi plants with FRK2-antisense plants to create double-mutant plants. The double-mutant plants exhibited novel phenotypes that were absent from the parent lines. About a third of the plants showed arrested shoot apical meristem around the transition to flowering and developed ectopic meristems. Use of the auxin reporter DR5::VENUS revealed a significantly reduced auxin response in the shoot apical meristems of the double-mutant, indicating that auxin levels were low. Altered inflorescence phyllotaxis and significant disorientation of vascular tissues were also observed. In addition, the fruits and the seeds of the double-mutant plants were very small and the seeds had very low germination rates. These results show that SUS1,3&4 and FRK2 enzymes are jointly essential for proper meristematic and vascular development, and for fruit and seed development.

A negative feedback loop of TOR signaling balances growth and stress-response trade-offs in plants

TOR kinase is a central coordinator of nutrient-dependent growth in eukaryotes. Maintaining optimal TOR signaling is critical for the normal development of organisms. In this study, we describe a negative feedback loop of TOR signaling helping in the adaptability of plants in changing environmental conditions. Using an interdisciplinary approach, we show that the plant-specific zinc finger protein FLZ8 acts as a regulator of TOR signaling in Arabidopsis. In sugar sufficiency, TOR-dependent and -independent histone modifications upregulate the expression of FLZ8. FLZ8 negatively regulates TOR signaling by promoting antagonistic SnRK1α1 signaling and bridging the interaction of SnRK1α1 with RAPTOR1B, a crucial accessory protein of TOR. This negative feedback loop moderates the TOR-growth signaling axis in the favorable condition and helps in the activation of stress signaling in unfavorable conditions, establishing its importance in the adaptability of plants.

MdbHLH3 modulates apple soluble sugar content by activating phosphofructokinase gene expression

Sugars are involved in plant growth, fruit quality, and signaling perception. Therefore, understanding the mechanisms involved in soluble sugar accumulation is essential to understand fruit development. Here, we report that MdPFPβ, a pyrophosphate-dependent phosphofructokinase gene, regulates soluble sugar accumulation by enhancing the photosynthetic performance and sugar-metabolizing enzyme activities in apple (Malus domestica Borkh.). Biochemical analysis revealed that a basic helix-loop-helix (bHLH) transcription factor, MdbHLH3, binds to the MdPFPβ promoter and activates its expression, thus promoting soluble sugar accumulation in apple fruit. In addition, MdPFPβ overexpression in tomato influenced photosynthesis and carbon metabolism in the plant. Furthermore, we determined that MdbHLH3 increases photosynthetic rates and soluble sugar accumulation in apple by activating MdPFPβ expression. Our results thus shed light on the mechanism of soluble sugar accumulation in apple leaves and fruit: MdbHLH3 regulates soluble sugar accumulation by activating MdPFPβ gene expression and coordinating carbohydrate allocation.

Sugar metabolism during pre- and post-fertilization events in plants under high temperature stress

High temperature challenges global crop production by limiting the growth and development of the reproductive structures and seed. It impairs the developmental stages of male and female gametogenesis, pollination, fertilization, endosperm formation and embryo development. Among these, the male reproductive processes are highly prone to abnormalities under high temperature at various stages of development. The disruption of source-sink balance is the main constraint for satisfactory growth of the reproductive structures which is disturbed at the level of sucrose import and utilization within the tissue. Seed development after fertilization is affected by modulation in the activity of enzymes involved in starch metabolism. In addition, the alteration in the seed-filling rate and its duration affects the seed weight and quality. The present review critically discusses the role of sugar metabolism in influencing the various stages of gamete and seed development under high temperature stress. It also highlights the interaction of the sugars with hormones that mediate the transport of sugars to sink tissues. The role of transcription factors for the regulation of sugar availability under high temperature has also been discussed. Further, the omics-based systematic investigation has been suggested to understand the synergistic or antagonistic interactions between sugars, hormones and reactive oxygen species at various points of sucrose flow from source to sink under high temperature stress.

Throttling Growth Speed: Evaluation of aux1-7 Root Growth Profile by Combining D-Root system and Root Penetration Assay

Directional root growth control is crucial for plant fitness. The degree of root growth deviation depends on several factors, whereby exogenous growth conditions have a profound impact. The perception of mechanical impedance by wild-type roots results in the modulation of root growth traits, and it is known that gravitropic stimulus influences distinct root movement patterns in concert with mechanoadaptation. Mutants with reduced shootward auxin transport are described as being numb towards mechanostimulus and gravistimulus, whereby different growth conditions on agar-supplemented medium have a profound effect on how much directional root growth and root movement patterns differ between wild types and mutants. To reduce the impact of unilateral mechanostimulus on roots grown along agar-supplemented medium, we compared the root movement of Col-0 and auxin resistant 1-7 in a root penetration assay to test how both lines adjust the growth patterns of evenly mechanostimulated roots. We combined the assay with the D-root system to reduce light-induced growth deviation. Moreover, the impact of sucrose supplementation in the growth medium was investigated because exogenous sugar enhances root growth deviation in the vertical direction. Overall, we observed a more regular growth pattern for Col-0 but evaluated a higher level of skewing of aux1-7 compared to the wild type than known from published data. Finally, the tracking of the growth rate of the gravistimulated roots revealed that Col-0 has a throttling elongation rate during the bending process, but aux1-7 does not.

Comprehensive Analysis of Long Non-coding RNA Modulates Axillary Bud Development in Tobacco (Nicotiana tabacum L.)

Long non-coding RNAs (lncRNAs) regulate gene expression and are crucial for plant growth and development. However, the mechanisms underlying the effects of activated lncRNAs on axillary bud development remain largely unknown. By lncRNA transcriptomes of axillary buds in topped and untopped tobacco plants, we identified a total of 13,694 lncRNAs. LncRNA analysis indicated that the promoted growth of axillary bud by topping might be partially ascribed to the genes related to hormone signal transduction and glycometabolism, trans-regulated by differentially expressed lncRNAs, such as MSTRG.52498.1, MSTRG.60026.1, MSTRG.17770.1, and MSTRG.32431.1. Metabolite profiling indicated that auxin, abscisic acid and gibberellin were decreased in axillary buds of topped tobacco lines, while cytokinin was increased, consistent with the expression levels of related lncRNAs. MSTRG.52498.1, MSTRG.60026.1, MSTRG.17770.1, and MSTRG.32431.1 were shown to be influenced by hormones and sucrose treatments, and were associated with changes of axillary bud growth in the overexpression of NtCCD8 plants (with reduced axillary buds) and RNA interference of NtTB1 plants (with increased axillary buds). Moreover, MSTRG.28151.1 was identified as the antisense lncRNA of NtTB1. Silencing of MSTRG.28151.1 in tobacco significantly attenuated the expression of NtTB1 and resulted in larger axillary buds, suggesting the vital function of MSTRG.28151.1 axillary bud developmen by NtTB1. Our findings shed light on lncRNA-mRNA interactions and their functional roles in axillary bud growth, which would improve our understanding of lncRNAs as important regulators of axillary bud development and plant architecture.

Glucose regulates cotton fiber elongation by interacting with brassinosteroid

In plants, glucose (Glc) plays important roles, as a nutrient and signal molecule, in the regulation of growth and development. However, the function of Glc in fiber development of upland cotton (Gossypium hirsutum) is unclear. Here, using gas chromatography-mass spectrometry (GC-MS), we found that the Glc content in fibers was higher than that in ovules during the fiber elongation stage. In vitro ovule culture revealed that lower Glc concentrations promoted cotton fiber elongation, while higher concentrations had inhibitory effects. The hexokinase inhibitor N-acetylglucosamine (NAG) inhibited cotton fiber elongation in the cultured ovules, indicating that Glc-mediated fiber elongation depends on the Glc signal transduced by hexokinase. RNA sequencing (RNA-seq) analysis and hormone content detection showed that 150mM Glc significantly activated brassinosteroid (BR) biosynthesis, and the expression of signaling-related genes was also increased, which promoted fiber elongation. In vitro ovule culture clarified that BR induced cotton fiber elongation in a dose-dependent manner. In hormone recovery experiments, only BR compensated for the inhibitory effects of NAG on fiber elongation in a Glc-containing medium. However, the ovules cultured with the BR biosynthetic inhibitor brassinazole and from the BR-deficient cotton mutant pag1 had greatly reduced fiber elongation at all the Glc concentrations tested. This demonstrates that Glc does not compensate for the inhibition of fiber elongation caused by BR biosynthetic defects, suggesting that the BR signaling pathway works downstream of Glc during cotton fiber elongation. Altogether, our study showed that Glc plays an important role in cotton fibre elongation, and crosstalk occurs between Glc and BR signaling during modulation of fiber elongation.

Critical factors influencing in vitro propagation and modulation of important secondary metabolites in Withania somnifera (L.) dunal

Withania somnifera (L.) Dunal is a valuable medicinal plant in the Solanaceae family. It is commonly known as Ashwagandha and is widely distributed around the globe. It has multiple pharmacological properties owing to the existence of diverse secondary metabolites viz., withanolide A, withanolide D, withaferin A, and withanone. It is in great demand in the herbal industry because of its extensive use. In this background, the major challenge lies in the rapid multiplication of elite cultivars of W. somnifera in order to produce genetically and phytoconstituents uniform plant material for pharmaceutical industries. Thus it is necessary to explore various biotechnological approaches for the clonal mass propagation and synthesis of pharmaceutically important constituents in W. somnifera. Though there are several studies on in vitro propagation on W. somnifera, yet many factors that critically influence the in vitro response and withanolides production need to be fine-tuned in the pretext of the existing knowledge. The current review focuses on the advancements and prospects in biotechnological interventions to meet the worldwide demands for W. somnifera and its bioactive compounds. This update on in vitro studies on W. somnifera will be useful to many researchers, entrepreneurs, and herbal industries looking for its in vitro mass multiplication and scientific utilization.

The Gene FvTST1 From Strawberry Modulates Endogenous Sugars Enhancing Plant Growth and Fruit Ripening

Sugar is an important carbon source and contributes significantly to the improvement of plant growth and fruit flavor quality. Sugar transport through the tonoplast is important for intracellular homeostasis and metabolic balance in plant cells. There are four tonoplast sugar transporters (FvTST1-4) in strawberry genome. The qRT-PCR results indicated that FvTST1 has a differential expression pattern in different tissues and developmental stages, and exhibited highest expression level in mature fruits. The yeast complementation assay showed that FvTST1 can mediate the uptake of different sugars, such as fructose, glucose, sucrose, and mannose. Subcellular localization analyses revealed that FvTST1 was mainly targeted to the tonoplast. Transient expression of FvTST1 in strawberry fruits enhanced both fruit ripening and sugar accumulation. Furthermore, FvTST1-transformed tomato plants exhibited higher sucrose and auxin content, enhanced seed germination and vegetative growth, higher photosynthetic rate, early flowering, and bore fruit; fructose and glucose levels were higher in transgenic fruits than those in the control. Transcriptomic analysis indicated that the auxin signaling pathway was highly enriched pathway in up-regulated Gene-ontology terms. In transgenic plants, genes encoding transcription factors, such as phytochrome-interacting factors PIF1, -3, and -4, as well as their potential target genes, were also induced. Collectively, the results show that FvTST1 enhances plant growth and fruit ripening by modulating endogenous sugars, and highlight the biological significance of this gene for future breeding purposes.

Role of sugar and auxin crosstalk in plant growth and development

Under the natural environment, nutrient signals interact with phytohormones to coordinate and reprogram plant growth and survival. Sugars are important molecules that control almost all morphological and physiological processes in plants, ranging from seed germination to senescence. In addition to their functions as energy resources, osmoregulation, storage molecules, and structural components, sugars function as signaling molecules and interact with various plant signaling pathways, such as hormones, stress, and light to modulate growth and development according to fluctuating environmental conditions. Auxin, being an important phytohormone, is associated with almost all stages of the plant's life cycle and also plays a vital role in response to the dynamic environment for better growth and survival. In the previous years, substantial progress has been made that showed a range of common responses mediated by sugars and auxin signaling. This review discusses how sugar signaling affects auxin at various levels from its biosynthesis to perception and downstream gene activation. On the same note, the review also highlights the role of auxin signaling in fine-tuning sugar metabolism and carbon partitioning. Furthermore, we discussed the crosstalk between the two signaling machineries in the regulation of various biological processes, such as gene expression, cell cycle, development, root system architecture, and shoot growth. In conclusion, the review emphasized the role of sugar and auxin crosstalk in the regulation of several agriculturally important traits. Thus, engineering of sugar and auxin signaling pathways could potentially provide new avenues to manipulate for agricultural purposes.

The hexokinase Gene Family in Cotton: Genome-Wide Characterization and Bioinformatics Analysis

Hexokinase (HXK) is involved in hexose phosphorylation, sugar sensing, and signal transduction, all of which regulate plant growth and adaptation to stresses. Gossypium hirsutum L. is one of the most important fiber crops in the world, however, little is known about the HXKs gene family in G. hirsutum L. We identified 17 GhHXKs from the allotetraploid G. hirsutum L. genome (AADD). G. raimondii (DD) and G. arboreum (AA) are the diploid progenitors of G. hirsutum L. and contributed equally to the At_genome and Dt_genome GhHXKs genes. The chromosomal locations and exon-intron structures of GhHXK genes among cotton species are conservative. Phylogenetic analysis grouped the HXK proteins into four and three groups based on whether they were monocotyledons and dicotyledons, respectively. Duplication event analysis demonstrated that HXKs in G. hirsutum L. primarily originated from segmental duplication, which prior to diploid hybridization. Experiments of qRT-PCR, transcriptome and promoter cis-elements demonstrated that GhHXKs' promoters have auxin and GA responsive elements that are highly expressed in the fiber initiation and elongation stages, while the promoters contain ABA-, MeJA-, and SA-responsive elements that are highly expressed during the synthesis of the secondary cell wall. We performed a comprehensive analysis of the GhHXK gene family is a vital fiber crop, which lays the foundation for future studies assessing its role in fiber development.

The interface of central metabolism with hormone signaling in plants

Amongst the myriad of metabolites produced by plants, primary metabolites and hormones play crucial housekeeping roles in the cell and are essential for proper plant growth and development. While the biosynthetic pathways of primary metabolism are well characterized, those of hormones are yet to be completely defined. Central metabolism provides precursors for hormone biosynthesis and the regulation and function of primary metabolites and hormones are tightly entwined. The combination of reverse genetics and technological advances in our ability to evaluate the levels of the molecular entities of the cell (transcripts, proteins and metabolites) has led to considerable improvements in our understanding of both the regulatory interaction between primary metabolites and hormones and its coordination in response to different conditions. Here, we provide an overview of the interaction of primary and hormone metabolism at the metabolic and signaling levels, as well as a perspective regarding the tools that can be used to tackle our current knowledge gaps at the signaling level.

Vacuolar fructose transporter SWEET17 is critical for root development and drought tolerance

Root growth and architecture are markedly influenced by both developmental and environmental cues. Sugars integrate different stimuli and are essential building blocks and signaling molecules for modulating the root system. Members from the SUGAR WILL EVENTUALLY BE EXPORTED TRANSPORTER (SWEET) family facilitate the transport of different sugars over cellular membranes and steer both inter and intracellular distribution of sugars. SWEET17 represents a fructose-specific sugar porter localized to the vacuolar membrane, the tonoplast. Here, we analyzed how SWEET17-dependent fructose released from vacuoles affects root growth during drought stress in Arabidopsis (Arabidopsis thaliana). We found that the SWEET17 gene was predominantly expressed in the root vasculature and in meristematic cells of the root tip. SWEET17 expression appeared markedly induced during lateral root (LR) outgrowth and under drought. Moreover, fructose repressed primary root growth but induced density and length of first order LRs. Consistently, sweet17 knock-out mutants exhibited reduced LR growth and a diminished expression of LR-development-related transcription factors during drought stress, resulting in impaired drought tolerance of sweet17 mutants. We discuss how SWEET17 activity integrates drought-induced cellular responses into fructose signaling necessary for modulation of the root system and maximal drought tolerance.

Lessons Learned from the Studies of Roots Shaded from Direct Root Illumination

The root is the below-ground organ of a plant, and it has evolved multiple signaling pathways that allow adaptation of architecture, growth rate, and direction to an ever-changing environment. Roots grow along the gravitropic vector towards beneficial areas in the soil to provide the plant with proper nutrients to ensure its survival and productivity. In addition, roots have developed escape mechanisms to avoid adverse environments, which include direct illumination. Standard laboratory growth conditions for basic research of plant development and stress adaptation include growing seedlings in Petri dishes on medium with roots exposed to light. Several studies have shown that direct illumination of roots alters their morphology, cellular and biochemical responses, which results in reduced nutrient uptake and adaptability upon additive stress stimuli. In this review, we summarize recent methods that allow the study of shaded roots under controlled laboratory conditions and discuss the observed changes in the results depending on the root illumination status.

Exogenous carbon source supplementation counteracts root and hypocotyl growth limitations under increased cotyledon shading, with glucose and sucrose differentially modulating growth curves

Plant growth is continuously modulated by endogenous and exogenous stimuli. By no means the only, but well described, signaling molecules produced in plants and distributed through the plant body to orchestrate efficient growth are photosynthates. Light is a potent exogenous stimulus that determines, first, the rate of photosynthesis, but also the rate of plant growth. Root meristem activity is reduced with direct illumination but enhanced with increased sugar levels. With reduced cotyledon illumination, the seedling increases hypocotyl elongation until adequate light exposure is again provided. If endogenous carbon sources are limited, this leads to a temporary inhibition of root growth. Experimental growth conditions include exogenous supplementation of sucrose or glucose in addition to culturing seedlings under light exposure in Petri dishes. We compared total root length and hypocotyl elongation of Arabidopsis thaliana wild type Col-0 in response to illumination status and carbon source in the growth medium. Overall, sucrose supplementation promoted hypocotyl and root length to a greater extent than glucose supplementation. Glucose promoted root length compared to non-supplemented seedlings especially when cotyledon illumination was greatly reduced.