RBOH-Dependent ROS Synthesis and ROS Scavenging by Plant Specialized Metabolites To Modulate Plant Development and Stress Responses

Roles of ROS and redox in regulating cell-to-cell communication: Spotlight on viral modulation of redox for local spread

Reactive oxygen species (ROS) are important signalling molecules that influence many aspects of plant biology. One way in which ROS influence plant growth and development is by modifying intercellular trafficking through plasmodesmata (PD). Viruses have evolved to use PD for their local cell-to-cell spread between plant cells, so it is therefore not surprising that they have found ways to modulate ROS and redox signalling to optimise PD function for their benefit. This review examines how intracellular signalling via ROS and redox pathways regulate intercellular trafficking via PD during development and stress. The relationship between viruses and ROS-redox systems, and the strategies viruses employ to control PD function by interfering with ROS-redox in plants is also discussed.

g-C3N4@CuO electrostatic self-assembly toward Ralstonia solanacearum: Insights from cytomembrane and motility disruption

BACKGROUND

Ralstonia solanacearum, a notorious and refractory bacterial plant pathogen, threatens multiple vegetable crops and causes significant economic loss in agriculture. Long-term use of traditional medicines not only increases the problem of drug resistance, but also causes great environmental pollution. Therefore, there is an urgent need to develop new agents with high efficacy and low toxicity.

RESULTS

In this study, we have synthesized and characterized graphitic carbon nitride incorporated copper oxide composite (g-C3N4@CuO), which showed higher antimicrobial effect than graphitic carbon nitride nanosheets (g-C3N4 nanosheets) and copper oxide nanoparticles (CuONPs). Ralstonia solanacearum exposed to g-C3N4@CuO exhibited higher levels of oxygen toxicity, cell membrane damage, DNA damage, motility disruption and even cell death compared to g-C3N4 nanosheets and CuONPs. In addition, g-C3N4@CuO was more effective in the control of tobacco bacterial wilt than g-C3N4 nanosheets and CuONPs.

CONCLUSION

Thus, this study provides a new perspective on g-C3N4@CuO control of bacterial diseases in crops, and the mechanism is related to the destruction of cell membrane damage and motility disruption. © 2024 Society of Chemical Industry.

Comparative transcriptomic insights into molecular mechanisms of the susceptibility wheat variety MX169 response to Puccinia striiformis f. sp. tritici (Pst) infection

Stripe rust of wheat is caused by the fungal pathogen Puccinia striiformis f. sp. tritici (Pst). Breeding durably resistant wheat varieties by disrupting the susceptibility (S) gene has an important impact on the control of wheat stripe rust. Mingxian169 (MX169) showed strong stripe rust susceptibility to all the races of Pst. However, molecular mechanisms and responsive genes underlying susceptibility of the wheat variety MX169 to Pst have not been elucidated. Here, we utilized next-generation sequencing technology to analyze transcriptomics data of "MX169" and high-resistance wheat "Zhong4" at 24, 48, and 120 h post-inoculation (hpi) with Pst. Comparative transcriptome analysis revealed 3,494, 2,831, and 2,700 differentially expressed genes (DEGs) at different time points. We observed an upregulation of DEGs involved in photosynthesis, flavonoid biosynthesis, pyruvate metabolism, thiamine metabolism, and other biological processes, suggesting their involvement in MX169's response to Pst. DEGs encoding transcription factors were also identified. Our study suggested the potential susceptibility gene resources in MX169 related to stripe rust response could be valuable for understanding the mechanisms involved in stripe rust susceptibility and for improving wheat resistance to Pst.

IMPORTANCE

Our study suggests the potential susceptibility gene resources in MX169 related to stripe rust response could be valuable for understanding the mechanisms involved in stripe rust susceptibility and for improving wheat resistance to Pst.

Integrated analyses of ionomics, phytohormone profiles, transcriptomics, and metabolomics reveal a pivotal role of carbon-nano sol in promoting the growth of tobacco plants

BACKGROUND

Carbon nano sol (CNS) can markedly affect the plant growth and development. However, few systematic analyses have been conducted on the underlying regulatory mechanisms in plants, including tobacco (Nicotiana tabacum L.).

RESULTS

Integrated analyses of phenome, ionome, transcriptome, and metabolome were performed in this study to elucidate the physiological and molecular mechanisms underlying the CNS-promoting growth of tobacco plants. We found that 0.3% CNS, facilitating the shoot and root growth of tobacco plants, significantly increased shoot potassium concentrations. Antioxidant, metabolite, and phytohormone profiles showed that 0.3% CNS obviously reduced reactive oxygen species production and increased antioxidant enzyme activity and auxin accumulation. Comparative transcriptomics revealed that the GO and KEGG terms involving responses to oxidative stress, DNA binding, and photosynthesis were highly enriched in response to exogenous CNS application. Differential expression profiling showed that NtNPF7.3/NtNRT1.5, potentially involved in potassium/auxin transport, was significantly upregulated under the 0.3% CNS treatment. High-resolution metabolic fingerprints showed that 141 and 163 metabolites, some of which were proposed as growth regulators, were differentially accumulated in the roots and shoots under the 0.3% CNS treatment, respectively.

CONCLUSIONS

Taken together, this study revealed the physiological and molecular mechanism underlying CNS-mediated growth promotion in tobacco plants, and these findings provide potential support for improving plant growth through the use of CNS.

Phytomelatonin maintained chromium toxicity induced oxidative burst in Brassica juncea L. through improving antioxidant system and gene expression

Chromium (Cr) contamination in soils reduces crop yields and poses a remarkable risk to human and plant system. The main objective of this study was to observe the protective mechanisms of exogenously applied melatonin (Mel- 0.05, 0.1, and 0.15 μM) in seedlings of Brassica juncea L. under Cr (0.2 mM) stress. This was accomplished by analysing the plant's morpho-physiological, biochemical, nuclear, membrane, and cellular characteristics, as well as electrolyte leakage. Superoxide, malondialdehyde, and hydrogen peroxide increased with Cr toxicity. Cr also increased electrolyte leakage. Seedlings under Cr stress had 86.4% more superoxide anion and 27.4% more hydrogen peroxide. Electrolyte leakage increased 35.7% owing to Cr toxicity. B. juncea L. cells with high radical levels had membrane and nuclear damage and decreased viability. Besides this, the activities of the antioxidative enzymes, as POD, APOX, SOD, GST, DHAR, GPOX and GR also elevated in the samples subjected to Cr toxicity. Conversely, the activity of catalase was downregulated due to Cr toxicity. In contrast, Mel reduced oxidative damage and conserved membrane integrity in B. juncea seedlings under Cr stress by suppressing ROS generation. Moreover, the activity of antioxidative enzymes that scavenge reactive oxygen species was substantially upregulated by the exogenous application of Mel. The highest concentration of Mel (Mel c- 0.15 μM) applied showed maximum ameliorative effect on the toxicity caused by Cr. It causes alleviation in the activity of SOD, CAT, POD, GPOX, APOX, DHAR, GST and GR by 51.32%, 114%, 26.44%, 48.91%, 87.51%, 149%, 42.30% and 40.24% respectively. Histochemical investigations showed that Mel increased cell survival and reduced ROS-induced membrane and nuclear damage. The findings showed that Mel treatment upregulated several genes, promoting plant development. Its supplementation decreased RBOH1 gene expression in seedling sunder stress. The results supported the hypothesis that Mel concentrations reduce Cr-induced oxidative burst in B. juncea.

Flavonols improve thermotolerance in tomato pollen during germination and tube elongation by maintaining ROS homeostasis

Elevated temperatures impair pollen performance and reproductive success, resulting in lower crop yields. The Solanum lycopersicum anthocyanin reduced ( are ) mutant has a FLAVANONE 3 HYDROXYLASE ( F3H ) gene mutation resulting in impaired synthesis of flavonol antioxidants. The are mutant has reduced pollen performance and seed set relative to the VF36 parental line, which is accentuated at elevated temperatures. Transformation of are with the wild-type F3H gene, or chemical complementation with flavonols, prevented temperature-dependent ROS accumulation in pollen and reversed are's reduced viability, germination, and tube elongation to VF36 levels. VF36 transformed with an F3H overexpression construct prevented temperature driven ROS increases and impaired pollen performance, revealing thermotolerance results from elevated flavonol synthesis. Although stigmas of are had reduced flavonols and elevated ROS, the growth of are pollen tubes were similarly impaired in both are and VF36 pistils. RNA-Seq was performed at optimal and stress temperatures in are , VF36, and the VF36 F3H overexpression line at multiple timepoints across pollen tube elongation. Differentially expressed gene numbers increased with duration of elevated temperature in all genotypes, with the largest number in are . These findings suggest potential agricultural interventions to combat the negative effects of heat-induced ROS in pollen that leads to reproductive failure.

One sentence summary

Flavonol antioxidants reduce the negative impacts of elevated temperatures on pollen performance by reducing levels of heat induced reactive oxygen species and modulation of heat-induced changes in the pollen transcriptome.

Reactive oxygen species are signaling molecules that modulate plant reproduction

Reactive oxygen species (ROS) can serve as signaling molecules that are essential for plant growth and development but abiotic stress can lead to ROS increases to supraoptimal levels resulting in cellular damage. To ensure efficient ROS signaling, cells have machinery to locally synthesize ROS to initiate cellular responses and to scavenge ROS to prevent it from reaching damaging levels. This review summarizes experimental evidence revealing the role of ROS during multiple stages of plant reproduction. Localized ROS synthesis controls the formation of pollen grains, pollen-stigma interactions, pollen tube growth, ovule development, and fertilization. Plants utilize ROS-producing enzymes such as respiratory burst oxidase homologs and organelle metabolic pathways to generate ROS, while the presence of scavenging mechanisms, including synthesis of antioxidant proteins and small molecules, serves to prevent its escalation to harmful levels. In this review, we summarized the function of ROS and its synthesis and scavenging mechanisms in all reproductive stages from gametophyte development until completion of fertilization. Additionally, we further address the impact of elevated temperatures induced ROS on impairing these reproductive processes and of flavonol antioxidants in maintaining ROS homeostasis to minimize temperature stress to combat the impact of global climate change on agriculture.

Decoding early stress signaling waves in living plants using nanosensor multiplexing

Increased exposure to environmental stresses due to climate change have adversely affected plant growth and productivity. Upon stress, plants activate a signaling cascade, involving multiple molecules like H2O2, and plant hormones such as salicylic acid (SA) leading to resistance or stress adaptation. However, the temporal ordering and composition of the resulting cascade remains largely unknown. In this study we developed a nanosensor for SA and multiplexed it with H2O2 nanosensor for simultaneous monitoring of stress-induced H2O2 and SA signals when Brassica rapa subsp. Chinensis (Pak choi) plants were subjected to distinct stress treatments, namely light, heat, pathogen stress and mechanical wounding. Nanosensors reported distinct dynamics and temporal wave characteristics of H2O2 and SA generation for each stress. Based on these temporal insights, we have formulated a biochemical kinetic model that suggests the early H2O2 waveform encodes information specific to each stress type. These results demonstrate that sensor multiplexing can reveal stress signaling mechanisms in plants, aiding in developing climate-resilient crops and pre-symptomatic stress diagnoses.

Spatial co-transcriptomics reveals discrete stages of the arbuscular mycorrhizal symbiosis

The symbiotic interaction of plants with arbuscular mycorrhizal (AM) fungi is ancient and widespread. Plants provide AM fungi with carbon in exchange for nutrients and water, making this interaction a prime target for crop improvement. However, plant-fungal interactions are restricted to a small subset of root cells, precluding the application of most conventional functional genomic techniques to study the molecular bases of these interactions. Here we used single-nucleus and spatial RNA sequencing to explore both Medicago truncatula and Rhizophagus irregularis transcriptomes in AM symbiosis at cellular and spatial resolution. Integrated, spatially registered single-cell maps revealed infected and uninfected plant root cell types. We observed that cortex cells exhibit distinct transcriptome profiles during different stages of colonization by AM fungi, indicating dynamic interplay between both organisms during establishment of the cellular interface enabling successful symbiosis. Our study provides insight into a symbiotic relationship of major agricultural and environmental importance and demonstrates a paradigm combining single-cell and spatial transcriptomics for the analysis of complex organismal interactions.

Arbuscular mycorrhizal fungal contribution towards plant resilience to drought conditions

Climate changes cause altering rainfall patterns resulting in an increase in drought occurrences globally. These events are disrupting plants and agricultural productivity. To evade droughts, plants try to adapt and modify in the best capacities possible. The plants have adapted by structurally modifying roots, stems, and leaves, as well as modifying functions. Lately, the association of microbial communities with plants has also been proven to be an important factor in aiding resilience. The fungal representatives of the microbial community also help safeguard the plants against drought. We discuss how these fungi associate with plants and contribute to evading drought stress. We specifically focus on Arbuscular mycorrhizal fungi (AMF) mediated mechanisms involving antioxidant defenses, phytohormone mediations, osmotic adjustments, proline expressions, fungal water absorption and transport, morphological modifications, and photosynthesis. We believe understanding the mechanisms would help us to optimize the use of fungi in agricultural practices. That way we could better prepare the plants for the anticipated future drought events.

Evolutionary Analysis of Six Gene Families Part of the Reactive Oxygen Species (ROS) Gene Network in Three Brassicaceae Species

Climate change is expected to intensify the occurrence of abiotic stress in plants, such as hypoxia and salt stresses, leading to the production of reactive oxygen species (ROS), which need to be effectively managed by various oxido-reductases encoded by the so-called ROS gene network. Here, we studied six oxido-reductases families in three Brassicaceae species, Arabidopsis thaliana as well as Nasturtium officinale and Eutrema salsugineum, which are adapted to hypoxia and salt stress, respectively. Using available and new genomic data, we performed a phylogenomic analysis and compared RNA-seq data to study genomic and transcriptomic adaptations. This comprehensive approach allowed for the gaining of insights into the impact of the adaptation to saline or hypoxia conditions on genome organization (gene gains and losses) and transcriptional regulation. Notably, the comparison of the N. officinale and E. salsugineum genomes to that of A. thaliana highlighted changes in the distribution of ohnologs and homologs, particularly affecting class III peroxidase genes (CIII Prxs). These changes were specific to each gene, to gene families subjected to duplication events and to each species, suggesting distinct evolutionary responses. The analysis of transcriptomic data has allowed for the identification of genes related to stress responses in A. thaliana, and, conversely, to adaptation in N. officinale and E. salsugineum.

Identification of NADPH Oxidase Genes Crucial for Rice Multiple Disease Resistance and Yield Traits

Reactive oxygen species (ROS) act as a group of signaling molecules in rice functioning in regulation of development and stress responses. Respiratory burst oxidase homologues (Rbohs) are key enzymes in generation of ROS. However, the role of the nine Rboh family members was not fully understood in rice multiple disease resistance and yield traits. In this study, we constructed mutants of each Rboh genes and detected their requirement in rice multiple disease resistance and yield traits. Our results revealed that mutations of five Rboh genes (RbohA, RbohB, RbohE, RbohH, and RbohI) lead to compromised rice blast disease resistance in a disease nursery and lab conditions; mutations of five Rbohs (RbohA, RbohB, RbohC, RbohE, and RbohH) result in suppressed rice sheath blight resistance in a disease nursery and lab conditions; mutations of six Rbohs (RbohA, RbohB, RbohC, RbohE, RbohH and RbohI) lead to decreased rice leaf blight resistance in a paddy yard and ROS production induced by PAMPs and pathogen. Moreover, all Rboh genes participate in the regulation of rice yield traits, for all rboh mutants display one or more compromised yield traits, such as panicle number, grain number per panicle, seed setting rate, and grain weight, resulting in reduced yield per plant except rbohb and rbohf. Our results identified the Rboh family members involved in the regulation of rice resistance against multiple pathogens that caused the most serious diseases worldwide and provide theoretical supporting for breeding application of these Rbohs to coordinate rice disease resistance and yield traits.

The hidden harmony: Exploring ROS-phytohormone nexus for shaping plant root architecture in response to environmental cues

Root system architecture, encompassing lateral roots and root hairs, plays a vital in overall plant growth and stress tolerance. Reactive oxygen species (ROS) and plant hormones intricately regulate root growth and development, serving as signaling molecules that govern processes such as cell proliferation and differentiation. Manipulating the interplay between ROS and hormones has the potential to enhance nutrient absorption, stress tolerance, and agricultural productivity. In this review, we delve into how studying these processes provides insights into how plants respond to environmental changes and optimize growth patterns to better control cellular processes and stress responses in crops. We discuss various factors and complex signaling networks that may exist among ROS and phytohormones during root development. Additionally, the review highlights possible role of reactive nitrogen species (RNS) in ROS-phytohormone interactions and in shaping root system architecture according to environmental cues.

VvATG6 contributes to copper stress tolerance by enhancing the antioxidant ability in transgenic grape calli

Autophagy, a conserved degradation and reuse process, plays a crucial role in plant cellular homeostasis during abiotic stress. Although numerous autophagy-related genes (ATGs) that regulate abiotic stress have been identified, few functional studies have shown how they confer tolerance to copper (Cu) stress. Here, we cloned a novel Vitis vinifera ATG6 gene (VvATG6) which was induced by 0.5 and 10 mM Cu stress based on transcriptomic data, and transgenic Arabidopsis thaliana, tobacco (Nicotiana tabacum), and grape calli were successfully obtained through Agrobacterium-mediated genetic transformation. The overexpression of VvATG6 enhanced the tolerance of transgenic lines to Cu. After Cu treatment, the lines that overexpressed VvATG6 grew better and increased their production of biomass compared with the wild-type. These changes were accompanied by higher activities of antioxidant enzymes and a lower accumulation of deleterious malondialdehyde and hydrogen peroxide in the transgenic plants. The activities of superoxide dismutase, peroxidase, and catalase were enhanced owing to the elevation of corresponding antioxidant gene expression in the VvATG6 overexpression plants under Cu stress, thereby promoting the clearance of reactive oxygen species (ROS). Simultaneously, there was a decrease in the levels of expression of RbohB and RbohC that are involved in ROS synthesis in transgenic plants under Cu stress. Thus, the accelerated removal of ROS and the inhibition of its synthesis led to a balanced ROS homeostasis environment, which alleviated the damage from Cu. This could benefit from the upregulation of other ATGs that are necessary for the production of autophagosomes under Cu stress. To our knowledge, this study is the first to demonstrate the protective role of VvATG6 in the Cu tolerance of plants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01415-y.

Nanoenabled Enhancement of Plant Tolerance to Heat and Drought Stress on Molecular Response

Global warming has posed significant pressure on agricultural productivity. The resulting abiotic stresses from high temperatures and drought have become serious threats to plants and subsequent global food security. Applying nanomaterials in agriculture can balance the plant's oxidant level and can also regulate phytohormone levels and thus maintain normal plant growth under heat and drought stresses. Nanomaterials can activate and regulate specific stress-related genes, which in turn increase the activity of heat shock protein and aquaporin to enable plants' resistance against abiotic stresses. This review aims to provide a current understanding of nanotechnology-enhanced plant tolerance to heat and drought stress. Molecular mechanisms are explored to see how nanomaterials can alleviate abiotic stresses on plants. In comparison with organic molecules, nanomaterials offer the advantages of targeted transportation and slow release. These advantages help the nanomaterials in mitigating drought and heat stress in plants.

Cross-Species Metabolomic Analyses in the Brassicaceae Reveals Common Responses to Ultraviolet-B Exposure

Exposure to UV-B radiation, an intrinsic component of solar light, is detrimental to all living organisms as chromophore units of DNA, RNA and proteins readily absorb high-energy photons. Indirect damage to the same molecules and lipids is mediated by elevated reactive oxygen species (ROS) levels, a side effect of exposure to UV-B stress. To protect themselves from UV-B radiation, plants produce phytochemical sunscreens, among which flavonoids have shown to be particularly effective. The core aglycone of flavonoid molecules is subjected to chemical decoration, such as glycosylation and acylation, further improving sunscreen properties. In particular, acylation, which adds a phenolic ring to flavonoid molecules, enhances the spectral absorption of UV-A and UV-B rays, providing to this class of compounds exceptional shielding power. In this study, we comprehensively analyzed the responses to UV-B radiation in four Brassicaceae species, including Arabidopsis thaliana, Brassica napus, Brassica oleracea, and Brassica rapa. Our study revealed a complete reprogramming of the central metabolic pathway in response to UV-B radiation characterized by increased production of functional precursors of specialized metabolites with UV-B shielding properties, indicating a targeted effort of plant metabolism to provide increased protection. The analysis of specialized metabolites and transcripts revealed the activation of the phenylpropanoid-acetate pathway, leading to the production of specific classes of flavonoids and a cross-species increase in phenylacylated-flavonoid glucosides with synapoyl glycoside decorations. Interestingly, our analysis also revealed that acyltransferase genes of the class of serine carboxypeptidase-like (SCPLs) proteins are costitutively expressed, but downregulated in response to UV-B radiation, possibly independently of the ELONGATED HYPOCOTYL 5 (HY5) signaling pathway.

Effects of Humic Substances and Mycorrhizal Fungi on Drought-Stressed Cactus: Focus on Growth, Physiology, and Biochemistry

Utilizing water resources rationally has become critical due to the expected increase in water scarcity. Cacti are capable of surviving with minimal water requirements and in poor soils. Despite being highly drought-resistant, cacti still faces limitations in realizing its full potential under drought-stress conditions. To this end, we investigated the interactive effect of humic substances (Hs) and arbuscular mycorrhizal fungi (AMF) on cactus plants under drought stress. In the study, a cactus pot experiment had three irrigation levels (W1: no irrigation, W2: 15% of field capacity, and W3: 30% of field capacity) and two biostimulants (Hs soil amendment and AMF inoculation), applied alone or combined. The findings show that the W1 and W2 regimes affected cactus performance. However, Hs and/or AMF significantly improved growth. Our results revealed that drought increased the generation of reactive oxygen species. However, Hs and/or AMF application improved nutrient uptake and increased anthocyanin content and free amino acids. Furthermore, the soil's organic matter, phosphorus, nitrogen, and potassium contents were improved by the application of these biostimulants. Altogether, using Hs alone or in combination with AMF can be an effective and sustainable approach to enhance the tolerance of cactus plants to drought conditions, while also improving the soil quality.

Seed Priming with Reactive Oxygen Species-Generating Nanoparticles Enhanced Maize Tolerance to Multiple Abiotic Stresses

Climate change-induced extreme weather events (heat, cold, drought, and flooding) will severely affect crop production. Increasing the resilience of crops to fluctuating environmental conditions is critically important. Here, we report that nanomaterials (NMs) with reactive oxygen species (ROS)-generating properties can be used as seed priming agents to simultaneously enhance the tolerance of maize seeds and seedlings to diverse and even multiple stresses. Maize seeds primed with 40 mg/L silver nanoparticles (AgNPs) exhibited accelerated seed germination and an increased germination rate, greater seedling vigor, and better seedling growth under drought (10% and 20% PEG), saline (50 and 100 mM NaCl), and cold (15 °C) stress conditions, indicating enhanced resilience to diverse stresses. Importantly, maize resistance to simultaneous multiple stresses (drought and cold, drought and salt, and salt and cold) was markedly enhanced. Under drought conditions, seed priming significantly boosted root hair density and length (17.3-82.7%), which enabled greater tolerance to water deficiency. RNA-seq analysis reveals that AgNPs seed priming induced a transcriptomic shift in maize seeds. Plant hormone signal transduction and MAPK signaling pathways were activated upon seed priming. Importantly, low-cost and environmentally friendly ROS-generating Fe-based NMs (Fe2O3 and Fe3O4 NPs) were also demonstrated to enhance the resistance of seeds and seedlings to drought, salt, and cold stresses. These findings demonstrate that a simple seed priming strategy can be used to significantly enhance the climate resilience of crops through modulated ROS homeostasis and that this approach could be a powerful nanoenabled tool for addressing worsening food insecurity.

Stress- and phospholipid signalling responses in Arabidopsis PLC4-KO and -overexpression lines under salt- and osmotic stress

Several drought and salt tolerant phenotypes have been reported when overexpressing (OE) phospholipase C (PLC) genes across plant species. In contrast, a negative role for Arabidopsis PLC4 in salinity stress was recently proposed, showing that roots of PLC4-OE seedlings were more sensitive to NaCl while plc4 knock-out (KO) mutants were more tolerant. To investigate this apparent contradiction, and to analyse the phospholipid signalling responses associated with salinity stress, we performed root growth- and phospholipid analyses on plc4-KO and PLC4-OE seedlings subjected to salinity (NaCl) or osmotic (sorbitol) stress and compared these with wild type (WT). Only very minor differences between PLC4 mutants and WT were observed, which even disappeared after normalization of the data, while in soil, PLC4-OE plants were clearly more drought tolerant than WT plants, as was found earlier when overexpressing Arabidopsis PLC2, -3, -5, -7 or -9. We conclude that PLC4 plays no opposite role in salt-or osmotic stress and rather behaves like the other Arabidopsis PLCs.

RsCDF3, a member of Cycling Dof Factors, positively regulates cold tolerance via auto-regulation and repressing two RsRbohs transcription in radish (Raphanus sativus L.)

Radish is one of the most economical root vegetable crops worldwide. Cold stress dramatically impedes radish taproot formation and development as well as reduces its yield and quality. Although the Cycling Dof Factors (CDFs) play crucial roles in plant growth, development and abiotic stress responses, how CDF TFs mediate the regulatory network of cold stress response remains largely unexplored in radish. Herein, a total of nine RsCDF genes were identified from the radish genome. Among them, the RsCDF3 exhibited obviously up-regulated expression under cold stress, especially at 12 h and 24 h. RsCDF3 was localized to the nucleus and displayed dramatic cold-induced promoter activity in tobacco leaves. Moreover, overexpression of RsCDF3 significantly enhanced cold tolerance of radish plants, whereas its knock-down plants exhibited the opposite phenotype. Interestingly, both in vitro and in vivo assays indicated that the RsCDF3 repressed the transcription of RsRbohA and RsRbohC via directly binding to their promoters, which contributed to maintaining the cellular homeostasis of reactive oxygen species (ROS) production and scavenging in radish. In addition, the RsCDF3 bound to its own promoter to mediate its transcription, thereby forming an autoregulatory feedback loop to cooperatively trigger RsRbohs-dependent cold tolerance. Together, we revealed a novel RsCDF3-RsRbohs module to promote the cold tolerance in radish plants. These findings would facilitate unveiling the molecular mechanism governing RsCDF3-mediated cold stress response in radish.

Pour some sugar on me: The diverse functions of phenylpropanoid glycosylation

The phenylpropanoid metabolism is the source of a vast array of specialized metabolites that play diverse functions in plant growth and development and contribute to all aspects of plant interactions with their surrounding environment. These compounds protect plants from damaging ultraviolet radiation and reactive oxygen species, provide mechanical support for the plants to stand upright, and mediate plant-plant and plant-microorganism communications. The enormous metabolic diversity of phenylpropanoids is further expanded by chemical modifications known as "decorative reactions", including hydroxylation, methylation, glycosylation, and acylation. Among these modifications, glycosylation is the major driving force of phenylpropanoid structural diversification, also contributing to the expansion of their properties. Phenylpropanoid glycosylation is catalyzed by regioselective uridine diphosphate (UDP)-dependent glycosyltransferases (UGTs), whereas glycosyl hydrolases known as β-glucosidases are the major players in deglycosylation. In this article, we review how the glycosylation process affects key physicochemical properties of phenylpropanoids, such as molecular stability and solubility, as well as metabolite compartmentalization/storage and biological activity/toxicity. We also summarize the recent knowledge on the functional implications of glycosylation of different classes of phenylpropanoid compounds. A balance of glycosylation/deglycosylation might represent an essential molecular mechanism to regulate phenylpropanoid homeostasis, allowing plants to dynamically respond to diverse environmental signals.

Ethanol suppresses rice seed germination through inhibiting ROS signaling

Ethanol is frequently used not only as priming but also as a solvent to dissolve hardly water-soluble phytohormones gibberellic acid (GA3) and abscisic acid (ABA) in seed germination. However, the molecular and physiological mechanisms of ethanol's impact on seed germination remain elusive. In this report, we investigated how ethanol affected reactive oxygen species (ROS) during rice seed germination. Ethanol at a concentration of 3.5% (v/v) inhibited 90% seed germination, which was almost reversed by H2O2. H2O2 contents in embryos were reduced by ethanol after 18 h imbibition. Antioxidant enzymes assays revealed that only superoxide dismutase (SOD) activities in seed embryos were lowered by ethanol, in line with the suppressed mRNA expression of SOD genes during imbibition. Additionally, compared to the mock condition, ethanol increased ABA contents but decreased GA (GA1 and GA3) in seed embryos, resulting in disharmonizing GA/ABA balance. Conceivably ethanol induced transcription of OsNCEDs, the key genes for ABA biosynthesis, and OsABA8ox3, a key gene for ABA catabolism. Furthermore, ethanol promoted ABA signaling by upregulating ABA receptor genes and ABA-responsive element (ABRE)-binding protein/ABRE-binding factors during imbibition. Overall, our results demonstrate that lowering of H2O2 levels due to suppressed SOD activities in rice germinating seed embryos is the decisive factor for ethanol-induced inhibition of seed germination, and GA/ABA balance and ABA signaling also play important roles in ethanol's inhibitory impact on seed germination.

PacBio Full-Length Transcriptome Sequencing Reveals the Mechanism of Salt Stress Response in Sonneratia apetala

Sonneratia apetala is an essential mangrove wetland restoration tree species. Studying its molecular mechanism for salt tolerance could lay a foundation for further cultivating excellent resistant germplasm. This study used a combination of PacBio isoform sequencing (Iso-seq) and BGISEQ RNA sequencing (RNA-seq) to analyze the molecular mechanism to salt stress response of one-year-old S. apetala leaves. The growth and physiological analysis showed that physiological indexes such as growth rate, net photosynthetic rate and antioxidant enzyme activity all exhibit significant changes under salt stress. From Iso-seq, a total of 295,501 full-length transcripts, with an average length of 1418 bp, were obtained. RNA-seq produced 4712 differentially expressed genes (DEGs) as compared to a control group. Of these, 930 were identified to be co-expressed during the STEM time sequence analysis. Further, 715 and 444 co-expressed DEGs were annotated by GO and KEGG analyses, respectively. Moreover, 318 of the co-expressed DEGs were annotated as essential genes that were implicated in salt stress response of S. apetala, which were involved in transcription factors, signal transduction, hormone response, ROS homeostasis, osmotic balance, cell wall synthesis or modification. These results provide candidate targets for further characterization and offer insights into the salt-tolerant mechanism of S. apetala.

Kiwifruit Resistance to Sclerotinia sclerotiorum and Pseudomonas syringae pv. actinidiae and Defence Induction by Acibenzolar-S-methyl and Methyl Jasmonate Are Cultivar Dependent

Pathogen susceptibility and defence gene inducibility were compared between the Actinidia arguta cultivar 'Hortgem Tahi' and the two cultivars of A. chinensis 'Hayward' and 'Zesy002'. Plants were treated with acibenzolar-s-methyl (ASM) or methyl jasmonate (MeJA) one week before inoculation with Pseudomonas syringae pv. actinidiae (Psa biovar3) or Sclerotinia sclerotiorum, or secondary induction with chitosan+glucan (Ch-Glu) as a potential pathogen proxy. Defence expression was evaluated by measuring the expression of 18 putative defence genes. 'Hortgem Tahi' was highly susceptible to sclerotinia and very resistant to Psa, whereas 'Zesy002' was highly resistant to both, and 'Hayward' was moderately susceptible to both. Gene expression in 'Hayward' and 'Zesy002' was alike but differed significantly from 'Hortgem Tahi' which had higher basal levels of PR1-i, PR5-i, JIH1, NPR3 and WRKY70 but lower expression of RD22 and PR2-i. Treatment with ASM caused upregulation of NIMIN2, PR1-i, WRKY70, DMR6 and PR5-i in all cultivars and induced resistance to Psa in 'Zesy002' and 'Hayward' but decreased resistance to sclerotinia in 'Zesy002'. MeJA application caused upregulation of LOX2 and downregulation of NIMIN2, DMR6 and PR2-i but did not affect disease susceptibility. The Ch-Glu inducer induced PR-gene families in each cultivar, highlighting its possible effectiveness as an alternative to actual pathogen inoculation. The significance of variations in fundamental and inducible gene expression among the cultivars is explored.

Integrated multi-omic data and analyses reveal the response pathways of to high-temperature stress

With the intensification of the greenhouse effect and the continuous rise of global temperature, high temperatures in summer seriously affect the growth of green onion (Allium fistulosum L.var.caespitosum Makino) and reduce its yield and quality. It is important to study the mechanism of heat tolerance in green onion for selecting and breeding new varieties with high-temperature tolerance. In this study, we used the heat-tolerant green onion variety AF60 and heat-sensitive green onion variety AF35 and measured their physiological indexes under different durations of heat stress. The results showed that high-temperature stress adversely affected the water content, protein composition and antioxidant system of green onion. In addition, a comprehensive analysis using transcriptomics and metabolomics showed that heat-tolerant green onions responded positively to heat stress by up-regulating the expression of heat shock proteins, whereas heat-sensitive green onions responded to heat stress by activating the galactose metabolic pathway and maintained normal physiological activities. This study revealed the physiological performance and high-temperature response pathways of different heat-tolerant green onion cultivars under heat stress. The results further deepen the understanding of the molecular mechanism of green onion's heat stress response.

ROS interplay between plant growth and stress biology: Challenges and future perspectives

In plants, reactive oxygen species (ROS) have emerged as a multifunctional signaling molecules that modulate diverse stress and growth responses. Earlier studies on ROS in plants primarily focused on its toxicity and ROS-scavenging processes, but recent findings are offering new insights on its role in signal perception and transduction. Further, the interaction of cell wall receptors, calcium channels, HATPase, protein kinases, and hormones with NADPH oxidases (respiratory burst oxidase homologues (RBOHs), provides concrete evidence that ROS regulates major signaling cascades in different cellular compartments related to stress and growth responses. However, at the molecular level there are many knowledge gaps regarding how these players influence ROS signaling and how ROS regulate them during growth and stress events. Furthermore, little is known about how plant sensors or receptors detect ROS under various environmental stresses and induce subsequent signaling cascades. In light of this, we provided an update on the role of ROS signaling in plant growth and stress biology. First, we focused on ROS signaling, its production and regulation by cell wall receptor like kinases. Next, we discussed the interplay between ROS, calcium and hormones, which forms a major signaling trio regulatory network of signal perception and transduction. We also provided an overview on ROS and nitric oxide (NO) crosstalk. Furthermore, we emphasized the function of ROS signaling in biotic, abiotic and mechanical stresses, as well as in plant growth and development. Finally, we conclude by highlighting challenges and future perspectives of ROS signaling in plants that warrants future investigation.

GhRCD1 regulates cotton somatic embryogenesis by modulating the GhMYC3-GhMYB44-GhLBD18 transcriptional cascade

Plant somatic embryogenesis (SE) is a multifactorial developmental process where embryos that can develop into whole plants are produced from somatic cells rather than through the fusion of gametes. The molecular regulation of plant SE, which involves the fate transition of somatic cells into embryogenic cells, is intriguing yet remains elusive. We deciphered the molecular mechanisms by which GhRCD1 interacts with GhMYC3 to regulate cell fate transitions during SE in cotton. While silencing of GhMYC3 had no discernible effect on SE, its overexpression accelerated callus formation, and proliferation. We identified two of GhMYC3 downstream SE regulators, GhMYB44 and GhLBD18. GhMYB44 overexpression was unconducive to callus growth but bolstered EC differentiation. However, GhLBD18 can be triggered by GhMYC3 but inhibited by GhMYB44, which positively regulates callus growth. On top of the regulatory cascade, GhRCD1 antagonistically interacts with GhMYC3 to inhibit the transcriptional function of GhMYC3 on GhMYB44 and GhLBD18, whereby a CRISPR-mediated rcd1 mutation expedites cell fate transition, resembling the effects of GhMYC3 overexpression. Furthermore, we showed that reactive oxygen species (ROS) are involved in SE regulation. Our findings elucidated that SE homeostasis is maintained by the tetrapartite module, GhRCD1-GhMYC3-GhMYB44-GhLBD18, which acts to modulate intracellular ROS in a temporal manner.

Examining the Transcriptomic and Biochemical Signatures of Bacillus subtilis Strains: Impacts on Plant Growth and Abiotic Stress Tolerance

Rhizobacteria from various ecological niches display variations in physiological characteristics. This study investigates the transcriptome profiling of two Bacillus subtilis strains, BsCP1 and BsPG1, each isolated from distinct environments. Gene expression linked to the synthesis of seven types of antibiotic compounds was detected in both BsCP1 and BsPG1 cultures. Among these, the genes associated with plipastatin synthesis were predominantly expressed in both bacterial strains. However, genes responsible for the synthesis of polyketide, subtilosin, and surfactin showed distinct transcriptional patterns. Additionally, genes involved in producing exopolysaccharides (EPS) showed higher expression levels in BsPG1 than in BsCP1. Consistently with this, a greater quantity of EPS was found in the BsPG1 culture compared to BsCP1. Both bacterial strains exhibited similar effects on Arabidopsis seedlings, promoting root branching and increasing seedling fresh weight. However, BsPG1 was a more potent enhancer of drought, heat, and copper stress tolerance than BsCP1. Treatment with BsPG1 had a greater impact on improving survival rates, increasing starch accumulation, and stabilizing chlorophyll content during the post-stress stage. qPCR analysis was used to measure transcriptional changes in Arabidopsis seedlings in response to BsCP1 and BsPG1 treatment. The results show that both bacterial strains had a similar impact on the expression of genes involved in the salicylic acid (SA) and jasmonic acid (JA) signaling pathways. Likewise, genes associated with stress response, root development, and disease resistance showed comparable responses to both bacterial strains. However, treatment with BsCP1 and BsPG1 induced distinct activation of genes associated with the ABA signaling pathway. The results of this study demonstrate that bacterial strains from different ecological environments have varying abilities to produce beneficial metabolites for plant growth. Apart from the SA and JA signaling pathways, ABA signaling triggered by PGPR bacterial strains could play a crucial role in building an effective resistance to various abiotic stresses in the plants they colonize.

Reactive oxygen species and NADPH oxidase-encoding genes underly the plant growth and developmental responses to Trichoderma

The modulation of plant growth and development through reactive oxygen species (ROS) is a hallmark during the interactions with microorganisms, but how fungi and their molecules influence endogenous ROS production in the root remains unknown. In this report, we correlated the biostimulant effect of Trichoderma atroviride with Arabidopsis root development via ROS signaling. T. atroviride enhanced ROS accumulation in primary root tips, lateral root primordia, and emerged lateral roots as revealed by total ROS imaging through the fluorescent probe H2DCF-DA and NBT detection. Acidification of the substrate and emission of the volatile organic compound 6-pentyl-2H-pyran-2-one appear to be major factors by which the fungus triggers ROS accumulation. Besides, the disruption of plant NADPH oxidases, also known as respiratory burst oxidase homologs (RBOHs) including ROBHA, RBOHD, but mainly RBOHE, impaired root and shoot fresh weight and the root branching enhanced by the fungus in vitro. RbohE mutant plants displayed poor lateral root proliferation and lower superoxide levels than wild-type seedlings in both primary and lateral roots, indicating a role for this enzyme for T. atroviride-induced root branching. These data shed light on the roles of ROS as messengers for plant growth and root architectural changes during the plant-Trichoderma interaction.

The protein phosphatase PC1 dephosphorylates and deactivates CatC to negatively regulate H2O2 homeostasis and salt tolerance in rice

Catalase (CAT) is often phosphorylated and activated by protein kinases to maintain hydrogen peroxide (H2O2) homeostasis and protect cells against stresses, but whether and how CAT is switched off by protein phosphatases remains inconclusive. Here, we identified a manganese (Mn2+)-dependent protein phosphatase, which we named PHOSPHATASE OF CATALASE 1 (PC1), from rice (Oryza sativa L.) that negatively regulates salt and oxidative stress tolerance. PC1 specifically dephosphorylates CatC at Ser-9 to inhibit its tetramerization and thus activity in the peroxisome. PC1 overexpressing lines exhibited hypersensitivity to salt and oxidative stresses with a lower phospho-serine level of CATs. Phosphatase activity and seminal root growth assays indicated that PC1 promotes growth and plays a vital role during the transition from salt stress to normal growth conditions. Our findings demonstrate that PC1 acts as a molecular switch to dephosphorylate and deactivate CatC and negatively regulate H2O2 homeostasis and salt tolerance in rice. Moreover, knockout of PC1 not only improved H2O2-scavenging capacity and salt tolerance but also limited rice grain yield loss under salt stress conditions. Together, these results shed light on the mechanisms that switch off CAT and provide a strategy for breeding highly salt-tolerant rice.

Hydrogen peroxide sensor HyPer7 illuminates tissue-specific plastid redox dynamics

The visualization of photosynthesis-derived reactive oxygen species has been experimentally limited to pH-sensitive probes, unspecific redox dyes, and whole-plant phenotyping. Recent emergence of probes that circumvent these limitations permits advanced experimental approaches to investigate in situ plastid redox properties. Despite growing evidence of heterogeneity in photosynthetic plastids, investigations have not addressed the potential for spatial variation in redox and/or reactive oxygen dynamics. To study the dynamics of H2O2 in distinct plastid types, we targeted the pH-insensitive, highly specific probe HyPer7 to the plastid stroma in Arabidopsis (Arabidopsis thaliana). Using HyPer7 and glutathione redox potential (EGSH) probe for redox-active green fluorescent protein 2 genetically fused to the redox enzyme human glutaredoxin-1 with live cell imaging and optical dissection of cell types, we report heterogeneities in H2O2 accumulation and redox buffering within distinct epidermal plastids in response to excess light and hormone application. Our observations suggest that plastid types can be differentiated by their physiological redox features. These data underscore the variation in photosynthetic plastid redox dynamics and demonstrate the need for cell-type-specific observations in future plastid phenotyping.

Genome-Wide Identification and Expression Analysis of Respiratory Burst Oxidase Homolog (RBOH) Gene Family in Eggplant (Solanum melongena L.) under Abiotic and Biotic Stress

Respiratory burst oxidase homologs (RBOHs) are important proteins that catalyze the production of reactive oxygen species (ROS), which play important roles in growth and stress response. For a comprehensive analysis of SmRBOH genes, we conducted genome-wide identification of the SmRBOH gene family in eggplant (Solanum melongena L.) and analyzed the expression of SmRBOHs under abiotic (salt, high-temperature, and low-temperature) and biotic stress (Verticillium dahliae inoculation) by quantitative real-time PCR (qRT-PCR). The result showed that a total of eight SmRBOH members were identified from the genome database of eggplant, and they were relatively evenly distributed across seven chromosomes. The analysis of Motif and the conserved domain showed that SmRBOHs have high similarity in protein sequences and functions. Based on phylogenetics, SmRBOHs were classified into three distinct clades. Furthermore, the promoter regions of SmRBOHs were found to contain different cis-elements. Additionally, the results of the qRT-PCR demonstrated differential expression patterns of SmRBOHs in different tissues (the roots, stems, and leaves) and stress conditions. SmRBOHB, SmRBOHD, SmRBOHH1, and SmRBOHH2 showed significant upregulation (>20-fold) under at least one stress condition. Subcellular localization analysis of the above four members further confirmed that they localized on the plasma membrane. This study provides a theoretical foundation for understanding the functions of SmRBOHs in eggplant.

Chemiluminescence-Based Assay to Monitor Early Oxidative Bursts in Soybean (Glycine max) Lateral Roots

The reactive oxygen species (ROS) burst assay is a valuable tool for studying pattern-triggered immunity (PTI) in plants. During PTI, the interaction between pathogen recognition receptors (PRRs) and pathogen-associated molecular patterns (PAMPs) leads to the rapid production of ROS in the apoplastic space. The resultant ROS can be measured using a chemiluminescent approach that involves the usage of horseradish peroxidase and luminol. Although several methods and protocols are available to detect early ROS bursts in leaf tissues, no dedicated method is available for root tissues. Here, we have established a reliable method to measure the PAMP-triggered ROS burst response in soybean lateral roots. In plants, lateral roots are the potential entry and colonization sites for pathogens in the rhizosphere. We have used important PAMPs such as chitohexaose, flagellin 22 peptide fragment, and laminarin to validate our method. In addition, we provide a detailed methodology for the isolation and application of fungal cell wall components to monitor the oxidative burst in soybean lateral roots. Furthermore, we provide methodology for performing ROS burst assays in soybean leaf discs with laminarin and fungal cell walls. This approach could also be applied to leaf and root tissues of other plant species to study the PTI response upon elicitor treatment. © 2023 Wiley Periodicals LLC. Basic Protocol: Reactive oxygen species (ROS) burst assay in soybean lateral root tissues Alternate Protocol: ROS burst assay in soybean leaf discs Support Protocol: Isolating fungal cell wall fractions.

Molecular Characterization of Defense of Brassica napus (Oilseed Rape) to Rhizoctonia solani AG2-1 Confirmed by Functional Analysis in Arabidopsis thaliana

Rhizoctonia solani is a necrotrophic, soilborne fungal pathogen associated with significant establishment losses in Brassica napus (oilseed rape; OSR). The anastomosis group (AG) 2-1 of R. solani is the most virulent to OSR, causing damping-off, root and hypocotyl rot, and seedling death. Resistance to R. solani AG2-1 in OSR has not been identified, and the regulation of OSR defense to its adapted pathogen, AG2-1, has not been investigated. In this work, we used confocal microscopy to visualize the progress of infection by sclerotia of AG2-1 on B. napus varieties with contrasting disease phenotypes. We defined their defense response using gene expression studies and functional analysis with Arabidopsis thaliana mutants. Our results showed existing variation in susceptibility to AG2-1 and plant growth between OSR varieties, and differential expression of genes of hormonal and defense pathways related to auxin, ethylene, jasmonic acid, abscisic acid, salicylic acid, and reactive oxygen species regulation. Auxin, abscisic acid signaling, and the MYC2 branch of jasmonate signaling contributed to the susceptibility to AG2-1, while induced systemic resistance was enhanced by NAPDH RBOHD, ethylene signaling, and the ERF/PDF branch of jasmonate signaling. These results pave the way for future research, which will lead to the development of Brassica crops that are more resistant to AG2-1 of R. solani and reduce dependence on chemical control options.

Full-Length Transcriptome Sequencing Reveals the Molecular Mechanism of Metasequoia glyptostroboides Seed Responding to Aging

Metasequoia glyptostroboides, Hu and W. C. Cheng, as the only surviving relict species of the Taxodiaceae Metasequoia genus, is a critically endangered and protected species in China. There is a risk of extinction due to the low vigor of M. glyptostroboides seeds, and the physiological mechanism of seed aging in M. glyptostroboides is not yet clear. In order to investigate the physiological and molecular mechanisms underlying the aging process of M. glyptostroboides seeds, we analyzed the antioxidant system and transcriptome at 0, 2, 4, 6, and 8 days after artificial accelerated aging treatment at 40 °C and 100% relative humidity. It was found that the germination percentage of fresh dried M. glyptostroboides seeds was 54 ± 5.29%, and significantly declined to 9.33 ± 1.88% after 6 days of aging, and then gradually decreased until the seed died on day 8. Superoxide dismutase (SOD) activity, ascorbic acid (AsA), glutathione (GSH) content and superoxide anion (O₂^·-) content and production rate significantly decreased, while malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) content and glutathione peroxidase (GPX) and catalase (CAT) activity gradually increased during the aging process. A total of 42,189 unigenes were identified in the whole transcriptome, and 40,446 (95.86%) unigenes were annotated in at least one protein database. A total of 15,376 differentially expressed genes (DEGs) were obtained; KEGG enrichment analysis results revealed that seed aging may be mainly involved in the protein-processing pathways in endoplasmic reticulum, oxidative phosphorylation, and ascorbate and aldarate metabolism. Weighted gene co-expression network analysis (WGCNA) revealed that the dark magenta, orange, and medium purple modules were highly correlated with physiological indicators such as SOD, CAT, and GSH and further identified 40 hub genes such as Rboh, ACO, HSF, and CML as playing important roles in the antioxidant network of M. glyptostroboides seeds. These findings provide a broader perspective for studying the regulatory mechanism of seed aging and a large number of potential target genes for the breeding of other endangered gymnosperms.

Changes in terpene biosynthesis and submergence tolerance in cotton

BACKGROUND

Flooding is among the most severe abiotic stresses in plant growth and development. The mechanism of submergence tolerance of cotton in response to submergence stress is unknown.

RESULTS

The transcriptome results showed that a total of 6,893 differentially expressed genes (DEGs) were discovered under submergence stress. Gene Ontology (GO) enrichment analysis showed that DEGs were involved in various stress or stimulus responses. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that DEGs related to plant hormone signal transduction, starch and sucrose metabolism, glycolysis and the biosynthesis of secondary metabolites were regulated by submergence stress. Eight DEGs related to ethylene signaling and 3 ethylene synthesis genes were identified in the hormone signal transduction. For respiratory metabolism, alcohol dehydrogenase (ADH, GH_A02G0728) and pyruvate decarboxylase (PDC, GH_D09G1778) were significantly upregulated but 6-phosphofructokinase (PFK, GH_D05G0280), phosphoglycerate kinase (PGK, GH_A01G0945 and GH_D01G0967) and sucrose synthase genes (SUS, GH_A06G0873 and GH_D06G0851) were significantly downregulated in the submergence treatment. Terpene biosynthetic pathway-related genes in the secondary metabolites were regulated in submergence stress.

CONCLUSIONS

Regulation of terpene biosynthesis by respiratory metabolism may play a role in enhancing the tolerance of cotton to submergence under flooding. Our findings showed that the mevalonate pathway, which occurs in the cytoplasm of the terpenoid backbone biosynthesis pathway (ko00900), may be the main response to submergence stress.

Regulation of reactive oxygen species and phytohormones in osmotic stress tolerance during seed germination in indica rice

Climate change due to global warming is now affecting agricultural production worldwide. In rice, one of the most important crops, water limitation due to irregular rainfall in rainfed lowlands during crop growth limits yield. Dry direct-sowing has been proposed as a water-efficient approach to cope with water stress during rice growth, but poor seedling establishment due to drought during germination and emergence is a problem. Here, we germinated indica rice cultivars Rc348 (drought tolerant) and Rc10 (drought sensitive) under osmotic stress induced by PEG to elucidate mechanisms of germination under drought. Rc348 had higher germination rate and germination index under severe osmotic stress of -1.5 MPa, above those of Rc10. Rc348 showed up-regulated GA biosynthesis, down-regulated ABA catabolism, and up-regulated α-amylase gene expression in imbibed seeds under PEG treatment compared to that of Rc10. During germination, reactive oxygen species (ROS) play important roles in antagonism between gibberellic acid (GA) and abscisic acid (ABA). Embryo of Rc348 treated with PEG had significantly greater expression of NADPH oxidase genes and higher endogenous ROS levels, together with significantly increased endogenous GA₁, GA₄ and ABA contents compared to that of Rc10. In aleurone layers treated with exogenous GA, expression of α-amylase genes was higher in Rc348 than in Rc10, and expression of NADPH oxidase genes was enhanced with significantly higher ROS content in Rc348, suggesting higher sensitivity of GA to ROS production and starch degradation in aleurone cells of Rc348. These results suggest that the osmotic stress tolerance of Rc348 is due to enhancement of ROS production, GA biosynthesis, and GA sensitivity, resulting in a higher germination rate under osmotic stress.

A prospective study of short-term apoplastic responses to ammonium treatment

The integration of external stimuli into plant cells has been extensively studied. Ammonium is a metabolic trigger because it affects plant nutrition status; on the contrary, it is also a stress factor inducing oxidative changes. Plants, upon quick reaction to the presence of ammonium, can avoid the development of toxicity symptoms, but their primary ammonium sensing mechanisms remain unknown. This study aimed to investigate the different signaling routes available in the extracellular space in response to supplying ammonium to plants. During short-term (30 min-24 h) ammonium treatment of Arabidopsis seedlings, no indication of oxidative stress development or cell wall modifications was observed. However, specific changes in reactive oxygen species (ROS) and redox status were observed in the apoplast, consequently leading to the activation of several ROS (RBOH, NQR), redox (MPK, OXI), and cell-wall (WAK, FER, THE, HERK) related genes. Therefore, it is expected that immediately after ammonium supply, a defense signaling route is initiated in the extracellular space. To conclude, the presence of ammonium is primarily perceived as a typical immune reaction.

Genome-wide identification of the myo-inositol oxygenase gene family in alfalfa (Medicago sativa L.) and expression analysis under abiotic stress

Myo-inositol oxygenase (MIOX), a pivotal enzyme in the myo-inositol oxygenation pathway, catalyzes the cleavage of myo-inositol to UDP-glucuronic acid and plays a major role in plant adaptation to abiotic stress factors. However, studies pertaining to the MIOX gene family in alfalfa (Medicago sativa L.) are lacking. Therefore, this study characterized ten MsMIOX genes in the alfalfa genome. These genes were divisible into two classes distributed over three chromosomes and produced 12 pairs of fragment repeats and one pair of tandem repeats. Physicochemical properties, subcellular location, protein structure, conserved motifs, and gene structure pertinent to these MsMIOX genes were analyzed. Construction of a phylogenetic tree revealed that similar gene structures and conserved motifs were present in the same MsMIOX groups. Analysis of cis-acting elements revealed the presence of stress- and hormone-induced expression elements in the promoter regions of the MsMIOX genes. qRT-PCR analysis revealed that MsMIOX genes could be induced by various abiotic stress factors, such as salt, saline-alkali, drought, and cold. Under such conditions, MIOX activity in alfalfa was significantly increased. Heterologous MsMIOX2 expression in yeast enhanced salt, saline-alkali, drought, and cold tolerance. Overexpression of MsMIOX2 in the hairy roots of alfalfa decreased O₂^- and H₂O₂ content and enhanced the abiotic stress tolerance. This study offers comprehensive perspectives on the functional features of the MsMIOX family and provides a candidate gene for improving the abiotic stress tolerance of alfalfa.

Abscisic acid increases hydrogen peroxide in mitochondria to facilitate stomatal closure

Abscisic acid (ABA) drives stomatal closure to minimize water loss due to transpiration in response to drought. We examined the subcellular location of ABA-increased accumulation of reactive oxygen species (ROS) in guard cells, which drive stomatal closure, in Arabidopsis (Arabidopsis thaliana). ABA-dependent increases in fluorescence of the generic ROS sensor, dichlorofluorescein (DCF), were observed in mitochondria, chloroplasts, cytosol, and nuclei. The ABA response in all these locations was lost in an ABA-insensitive quintuple receptor mutant. The ABA-increased fluorescence in mitochondria of both DCF- and an H2O2-selective probe, Peroxy Orange 1, colocalized with Mitotracker Red. ABA treatment of guard cells transformed with the genetically encoded H2O2 reporter targeted to the cytoplasm (roGFP2-Orp1), or mitochondria (mt-roGFP2-Orp1), revealed H2O2 increases. Consistent with mitochondrial ROS changes functioning in stomatal closure, we found that guard cells of a mutant with mitochondrial defects, ABA overly sensitive 6 (abo6), have elevated ABA-induced ROS in mitochondria and enhanced stomatal closure. These effects were phenocopied with rotenone, which increased mitochondrial ROS. In contrast, the mitochondrially targeted antioxidant, MitoQ, dampened ABA effects on mitochondrial ROS accumulation and stomatal closure in Col-0 and reversed the guard cell closure phenotype of the abo6 mutant. ABA-induced ROS accumulation in guard cell mitochondria was lost in mutants in genes encoding respiratory burst oxidase homolog (RBOH) enzymes and reduced by treatment with the RBOH inhibitor, VAS2870, consistent with RBOH machinery acting in ABA-increased ROS in guard cell mitochondria. These results demonstrate that ABA elevates H2O2 accumulation in guard cell mitochondria to promote stomatal closure.

GA signaling protein LsRGL1 interacts with the abscisic acid signaling-related gene LsWRKY70 to affect the bolting of leaf lettuce

A variety of endogenous hormone signals, developmental cues, and environmental stressors can trigger and promote leaf lettuce bolting. One such factor is gibberellin (GA), which has been linked to bolting. However, the signaling pathways and the mechanisms that regulate the process have not been discussed in full detail. To clarify the potential role of GAs in leaf lettuce, significant enrichment of GA pathway genes was found by RNA-seq, among which the LsRGL1 gene was considered significant. Upon overexpression of LsRGL1, a noticeable inhibition of leaf lettuce bolting was observed, whereas its knockdown by RNA interference led to an increase in bolting. In situ hybridization analysis indicated a significant accumulation of LsRGL1 in the stem tip cells of overexpressing plants. Leaf lettuce plants stably expressing LsRGL1 were examined concerning differentially expressed genes through RNA-seq analysis, and the data indicated enhanced enrichment of these genes in the 'plant hormone signal transduction' and 'phenylpropanoid biosynthesis' pathways. Additionally, significant changes in LsWRKY70 gene expression were identified in COG (Clusters of Orthologous Groups) functional classification. The results of yeast one-hybrid, β-glucuronidase (GUS), and biolayer interferometry (BLI) experiments showed that LsRGL1 proteins directly bind to the LsWRKY70 promoter. Silencing LsWRKY70 by virus-induced gene silencing (VIGS) can delay bolting, regulate the expression of endogenous hormones, abscisic acid (ABA)-linked genes, and flowering genes, and improve the nutritional quality of leaf lettuce. These results strongly associate the positive regulation of bolting with LsWRKY70 by identifying its vital functions in the GA-mediated signaling pathway. The data obtained in this research are invaluable for further experiments concerning the development and growth of leaf lettuce.

Brachypodium BdCHS is a homolog of Arabidopsis AtCHS involved in the synthesis of flavonoids and lateral root development

Flavonoids are a kind of plant-specific secondary metabolites, which play an important role in regulating plant growth and development, stress response, and also have medicinal value. Chalcone synthase is the key enzyme in the synthesis of flavonoids. The function of chalcone synthase in Arabidopsis thaliana has been well studied, but its homologous protein in Brachypodium distachyon has not been reported. In this study, we identified a homolog of AtCHS in B. distachyon, named BdCHS, and described its function. Phylogenetic tree analysis showed that BdCHS was most closely related to CHS in Triticum aestivum. Transgene analysis revealed that BdCHS protein was localized in the cytoplasm of Arabidopsis root cells. BdCHS protein can complement the phenotype of AtCHS mutants with lighter seed coat color and increased lateral root density. The content of superoxide anion in the cortical cells above the lateral root primordium in AtCHS mutants was higher than that in the wild-type, and BdCHS protein could restore the content of superoxide anion in AtCHS mutant to the level of that in the wild-type. The results showed that BdCHS was a functional homolog of AtCHS, which laid a foundation for the subsequent application of BdCHS in genetic breeding and crop improvement.

Interplay between membrane proteins and membrane protein-lipid pertaining to plant salinity stress

High salinity in agricultural lands is one of the predominant issues limiting agricultural yields. Plants have developed several mechanisms to withstand salinity stress, but the mechanisms are not effective enough for most crops to prevent and persist the salinity stress. Plant salt tolerance pathways involve membrane proteins that have a crucial role in sensing and mitigating salinity stress. Due to a strategic location interfacing two distinct cellular environments, membrane proteins can be considered checkpoints to the salt tolerance pathways in plants. Related membrane proteins functions include ion homeostasis, osmosensing or ion sensing, signal transduction, redox homeostasis, and small molecule transport. Therefore, modulating plant membrane proteins' function, expression, and distribution can improve plant salt tolerance. This review discusses the membrane protein-protein and protein-lipid interactions related to plant salinity stress. It will also highlight the finding of membrane protein-lipid interactions from the context of recent structural evidence. Finally, the importance of membrane protein-protein and protein-lipid interaction is discussed, and a future perspective on studying the membrane protein-protein and protein-lipid interactions to develop strategies for improving salinity tolerance is proposed.

Multi-copper oxidases SKU5 and SKS1 coordinate cell wall formation using apoplastic redox-based reactions in roots

The primary cell wall is a fundamental plant constituent that is flexible but sufficiently rigid to support the plant cell shape. Although many studies have demonstrated that reactive oxygen species (ROS) serve as important signaling messengers to modify the cell wall structure and affect cellular growth, the regulatory mechanism underlying the spatial-temporal regulation of ROS activity for cell wall maintenance remains largely unclear. Here, we demonstrate a role of the Arabidopsis (Arabidopsis thaliana) multi-copper oxidase-like protein skewed 5 (SKU5) and its homolog SKU5-similar 1 (SKS1) in root cell wall formation through modulating ROS homeostasis. Loss of SKU5 and SKS1 function resulted in aberrant division planes, protruding cell walls, ectopic deposition of iron, and NADPH oxidase-dependent ROS overproduction in the root epidermis-cortex and cortex-endodermis junctions. A decrease of ROS level or inhibition of NADPH oxidase activity rescued the cell wall defects of sku5 sks1 double mutants. SKU5 and SKS1 proteins were activated by iron treatment, and iron over-accumulated in the walls between root epidermis and cortex cell layers of sku5 sks1. The glycosylphosphatidylinositol-anchored motif was crucial for membrane association and functionality of SKU5 and SKS1. Overall, our results identified SKU5 and SKS1 as regulators of ROS at the cell surface for regulation of cell wall structure and root cell growth.

Flavonols modulate plant development, signaling, and stress responses

Flavonols are plant-specialized metabolites with important functions in plant growth and development. Isolation and characterization of mutants with reduced flavonol levels, especially the transparent testa mutants in Arabidopsis thaliana, have contributed to our understanding of the flavonol biosynthetic pathway. These mutants have also uncovered the roles of flavonols in controlling development in above- and below-ground tissues, notably in the regulation of root architecture, guard cell signaling, and pollen development. In this review, we present recent progress made towards a mechanistic understanding of flavonol function in plant growth and development. Specifically, we highlight findings that flavonols act as reactive oxygen species (ROS) scavengers and inhibitors of auxin transport in diverse tissues and cell types to modulate plant growth and development and responses to abiotic stresses.

Role of reactive oxygen species in the modulation of auxin flux and root development in Arabidopsis thaliana

Reactive oxygen species (ROS) play a dual role in plant biology, acting as important signal transduction molecules and as toxic byproducts of aerobic metabolism that accumulate in cells upon exposure to different stressors and lead to cell death. In plants, root architecture is regulated by the distribution and intercellular flow of the phytohormone auxin. In this study, we identified ROS as an important modulator of auxin distribution and response in the root. ROS production is necessary for root growth, proper tissue patterning, cell growth, and lateral root (LR) induction. Alterations in ROS balance led to altered auxin distribution and response in SOD and RHD2 loss-of-function mutants. Treatment of Arabidopsis seedlings with additional sources of ROS (hydrogen peroxide) or an ROS production inhibitor (diphenylene iodonium) induced phenocopies of the mutants studied. Simultaneous application of auxin and ROS increased LR primordia induction, and PIN-FORMED protein immunolocalization further demonstrated the existing link between auxin and ROS in orchestrating cell division and auxin flux during root development. In Arabidopsis roots, genetic alterations in ROS balance led to defective auxin distribution and growth-related responses in roots. Exogenous hydrogen peroxide alters the establishment of the endogenous auxin gradient in the root meristem through regulation of PIN-FORMED polarity, while the simultaneous application of hydrogen peroxide and auxin enhanced LR induction in a dose- and position-dependent manner through activation of cell division.

Physiological and molecular mechanism of ginger (Zingiber officinale Roscoe) seedling response to salt stress

We used 'Shannong No.1' experimental material to simulate higher salt concentration in ginger and analyzed the physiological responses of different parts of ginger seedlings under salt stress. The results showed that salt stress led to a significant decrease in fresh and dry weight of ginger, lipid membrane peroxidation, increased sodium ion content and enhanced activity of antioxidant enzymes. Compared with the control, the overall plant dry weight of ginger under salt stress decreased by about 60%, and the MDA content in roots, stems, leaves, and rhizomes increased by 372.27%, 184.88%, 291.5%, and 171.13%, respectively, and the APX content increased by 188.85%, 165.56%, 195.38%, and 40.08%, respectively. After analysis of the physiological indicators, it was found that the roots and leaves of ginger were the most significantly changed parts. We analyzed the transcriptional differences between ginger roots and leaves by RNA-seq and found that they jointly initiated MAPK signaling pathways in response to salt stress. By combining physiological and molecular indicators, we elucidated the response of different tissues and parts of ginger to salt stress during the seedling stage.

Untargeted profiling of secondary metabolites and phytotoxins associated with stemphylium blight of lentil

Stemphylium botryosum alters lentil secondary metabolism and differentially affects resistant and susceptible genotypes. Untargeted metabolomics identifies metabolites and their potential biosynthetic pathways that play a crucial role in resistance to S. botryosum. The molecular and metabolic processes that mediate resistance to stemphylium blight caused by Stemphylium botryosum Wallr. in lentil are largely unknown. Identifying metabolites and pathways associated with Stemphylium infection may provide valuable insights and novel targets to breed for enhanced resistance. The metabolic changes following infection of four lentil genotypes by S. botryosum were investigated by comprehensive untargeted metabolic profiling employing reversed-phase or hydrophilic interaction liquid chromatography (HILIC) coupled to a Q-Exactive mass spectrometer. At the pre-flowering stage, plants were inoculated with S. botryosum isolate SB19 spore suspension and leaf samples were collected at 24, 96 and 144 h post-inoculation (hpi). Mock-inoculated plants were used as negative controls. After analyte separation, high-resolution mass spectrometry data was acquired in positive and negative ionization modes. Multivariate modeling revealed significant treatment, genotype and hpi effects on metabolic profile changes that reflect lentil response to Stemphylium infection. In addition, univariate analyses highlighted numerous differentially accumulated metabolites. By contrasting the metabolic profiles of SB19-inoculated and mock-inoculated plants and among lentil genotypes, 840 pathogenesis-related metabolites were detected including seven S. botryosum phytotoxins. These metabolites included amino acids, sugars, fatty acids and flavonoids in primary and secondary metabolism. Metabolic pathway analysis revealed 11 significant pathways including flavonoid and phenylpropanoid biosynthesis, which were affected upon S. botryosum infection. This research contributes to ongoing efforts toward a comprehensive understanding of the regulation and reprogramming of lentil metabolism under biotic stress, which will provide targets for potential applications in breeding for enhanced disease resistance.

Calcium lignosulfonate modulates physiological and biochemical responses to enhance shoot multiplication in Vanilla planifolia Andrews

Utilisation of calcium lignosulfonate (CaLS) in Vanilla planifolia has been reported to improve shoot multiplication. However, mechanisms responsible for such observation remain unknown. Here, we elucidated the underlying mechanisms of CaLS in promoting shoot multiplication of V. planifolia via comparative proteomics, biochemical assays, and nutrient analysis. The proteome profile of CaLS-treated plants showed enhancement of several important cellular metabolisms such as photosynthesis, protein synthesis, Krebs cycle, glycolysis, gluconeogenesis, and carbohydrate synthesis. Further biochemical analysis recorded that CaLS increased Rubisco activity, hexokinase activity, isocitrate dehydrogenase activity, total carbohydrate content, glutamate synthase activity and total protein content in plant shoot, suggesting the role of CaLS in enhancing shoot growth via upregulation of cellular metabolism. Subsequent nutrient analysis showed that CaLS treatment elevated the contents of several nutrient ions especially calcium and sodium ions. In addition, our study also revealed that CaLS successfully maintained the cellular homeostasis level through the regulation of signalling molecules such as reactive oxygen species and calcium ions. These results demonstrated that the CaLS treatment can enhance shoot multiplication in V. planifolia Andrews by stimulating nutrient uptake, inducing cell metabolism, and regulating cell homeostasis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01293-w.