Gibberellin mediates spermidine-induced salt tolerance and the expression of GT-3b in cucumber

Single-cell transcriptomic analysis reveals the developmental trajectory and transcriptional regulatory networks of quinoa salt bladders

Salt bladders, specialized structures on the surface of quinoa leaves, secrete Na+ to mitigate the effects of the plant from abiotic stresses, particularly salt exposure. Understanding the development of these structures is crucial for elucidating quinoa's salt tolerance mechanisms. In this study, we employed transmission electron microscopy to detail cellular differentiation across the developmental stages of quinoa salt bladders. To further explore the developmental trajectory and underlying molecular mechanisms, we conducted single-cell RNA sequencing on quinoa protoplasts derived from young leaves. This allowed us to construct a cellular atlas, identifying 13 distinct cell clusters. Through pseudotime analysis, we mapped the developmental pathways of salt bladders and identified regulatory factors involved in cell fate decisions. GO and KEGG enrichment analyses, as well as experimental results, revealed the impacts of salt stress and the deprivation of sulfur and nitrogen on the development of quinoa salt bladders. Analysis of the transcription factor interaction network in pre-stalk cells (pre-SC), stalk cells (SC), and epidermal bladder cells (EBCs) indicated that TCP5, YAB5, NAC078, SCL8, GT-3B, and T1P17.40 play crucial roles in EBC development. Based on our findings, we developed an informative model elucidating salt bladder formation. This study provides a vital resource for mapping quinoa leaf cells and contributes to our understanding of its salt tolerance mechanisms.

The role of gibberellin synthase gene VvGA2ox7 acts as a positive regulator to salt stress in Arabidopsis thaliana

BACKGROUND

Soil salinity is an important environmental component affecting plant growth and yield, but high-salinity soils are a major constraint to the development of the grape industry. Previous studies have provided lines of evidence that gibberellins (GAs) play a significant regulatory role in plant responses to salt stress. However, it remains unclear whether GA2ox, a key enzyme that maintains the balance of bioactive gibberellins and intermediates in plants, is involved in the mechanism of salt stress tolerance in grapes.

RESULTS

In this study, we found that GA2ox7 positively modulates salt stress via its ectopic expression in Arabidopsis thaliana. The GA2ox7 gene cloned from grape was a hydrophilic protein, its CDS length was 1002 bp. Besides, VvGA2ox7 protein contained DIOX_N and 2OG-FeII_Oxy domains and was localized at the nucleus and cytoplasm. Yeast two-hybrid (Y2H) showed VvARCN1, VvB5R, VvRUB2, and VvCAR11 might be potential interaction proteins of VvGA2ox7. Compared with the wild type, overexpression of VvGA2ox7 in Arabidopsis thaliana enhanced antioxidant enzymatic activities and proline, chlorophyll, and ABA contents, and decreased relative electrical conductivity, malondialdehyde, and GA3 contents. Moreover, overexpression of VvGA2ox7 positively regulated the expression of salt stress response genes (KAT1, APX1, LEA, P5CS1, AVP1, CBF1), indicating that the VvGA2ox7 overexpression improved the salt stress tolerance of plants.

CONCLUSIONS

Taken together, this investigation indicates that VvGA2ox7 may act as a positive regulator in response to salt stress and provide novel insights for a deeper understanding of the role of VvGA2ox7 in grapes.

Regulatory mechanisms of miR171d-SCL6 module in the rooting process of Acer rubrum L

MAIN CONCLUSION

MiR171d and SCL6 are induced by the plant hormone auxin. MiR171d negatively regulates the expression of SCL6, thereby regulating the growth and development of plant adventitious roots. Under natural conditions, it is difficult to induce rooting in the process of propagating Acer rubrum L. via branches, which seriously limits its wide application in landscaping construction. In this study, the expression of Ar-miR171d was downregulated and the expression of ArSCL6 was upregulated after 300 mg/L indole-3-butyric acid (IBA) treatment. The transient interaction of Ar-miR171d and ArSCL6 in tobacco cells further confirmed their cleavage activity. Transgenic function verification confirmed that OE-Ar-miR171d inhibited adventitious root (AR) development, while OE-ArSCL6 promoted AR development. Tissue-specific expression verification of the ArSCL6 promoter demonstrated that it was specifically expressed in the plant root and leaf organs. Subcellular localization and transcriptional activation assays revealed that both ArSCL6 and ArbHLH089 were located in the nucleus and exhibited transcriptional activation activity. The interaction between the two was verified by bimolecular fluorescence complementarity (BIFC) experiments. These results help elucidate the regulatory mechanisms of the Ar-miR171d-ArSCL6 module during the propagation of A. rubrum and provide a molecular basis for the rooting of branches.

Fine mapping and identification of ERF transcription factor ERF017 as a candidate gene for cold tolerance in pumpkin

KEY MESSAGE

Two major QTLs for cold tolerance in pumpkin were localised, and CmoERF017 was identified as a key candidate gene within these QTLs via RNA-seq. Functional analysis revealed that CmoERF017 was a positive regulator of pumpkin in response to low-temperature stress. Low temperature is a key environmental factor that affects the protected cultivation of cucumber (Cucumis sativus L.) in winter, and the cold tolerance of cucumber/pumpkin-grafted seedlings depends on the rootstock. Pumpkin (Cucurbita spp.) has a well-developed root system, high resistance and wide adaptation, commonly used as rootstock for cucumber to improve the cold tolerance of grafted seedlings. This study used two high-generation inbred lines of Cucurbita moschata with significant differences in cold tolerance. We identified key candidate genes within the major cold tolerance QTL of rootstocks using QTL-seq and RNA-seq and investigated the function and molecular mechanisms of these genes in response to low-temperature stress. Results showed that QTL-seq located two cold tolerance QTLs, qCII-1 and qCII-2, while RNA-seq located 28 differentially expressed genes within these QTLs. CmoERF017 was finally identified as a key candidate gene. Functional validation results indicated that CmoERF017 is a positive regulator of pumpkin in response to low-temperature stress and affected root ABA synthesis and signalling by directly regulating the expression of SDR7 and ABI5. This study identified a key gene for low-temperature stress tolerance in rootstock pumpkin and clarified its role in the molecular mechanism of hormone-mediated plant cold tolerance. The study findings enrich the theoretical understanding of low-temperature stress tolerance in pumpkin and are valuable for the selection and breeding of cold-tolerant varieties of pumpkin used for rootstocks.

Spermidine Improves Freezing Tolerance by Regulating H2O2 in Brassica napus L

Low temperature is a common abiotic stress that causes significant damage to crop production. Polyamines (PAs) are a class of aliphatic amine compounds that serve as regulatory molecules involved in plant growth, development, and response to abiotic and biotic stresses. In this study, we found that the exogenous application of two concentrations of spermidine (Spd) significantly enhanced the freezing tolerance of three differently matured rapeseed (Brassica napus L.) varieties, as manifested by higher survival rates, lower freezing injury indexes, and reduced H2O2 content. RNA-seq and qRT-PCR analyses showed that Spd enhanced the freezing tolerance of rapeseed by regulating genes related to the PA metabolic pathway and antioxidant mechanism, and generally inhibited the expression of genes related to the JA signaling pathway. This study provides a reference basis for understanding the functionality and molecular mechanisms of polyamines in the response of rapeseed to freezing stress.

Research Advancements in Salt Tolerance of Cucurbitaceae: From Salt Response to Molecular Mechanisms

Soil salinization severely limits the quality and productivity of economic crops, threatening global food security. Recent advancements have improved our understanding of how plants perceive, signal, and respond to salt stress. The discovery of the Salt Overly Sensitive (SOS) pathway has been crucial in revealing the molecular mechanisms behind plant salinity tolerance. Additionally, extensive research into various plant hormones, transcription factors, and signaling molecules has greatly enhanced our knowledge of plants' salinity tolerance mechanisms. Cucurbitaceae plants, cherished for their economic value as fruits and vegetables, display sensitivity to salt stress. Despite garnering some attention, research on the salinity tolerance of these plants remains somewhat scattered and disorganized. Consequently, this article offers a review centered on three aspects: the salt response of Cucurbitaceae under stress; physiological and biochemical responses to salt stress; and the current research status of their molecular mechanisms in economically significant crops, like cucumbers, watermelons, melon, and loofahs. Additionally, some measures to improve the salt tolerance of Cucurbitaceae crops are summarized. It aims to provide insights for the in-depth exploration of Cucurbitaceae's salt response mechanisms, uncovering the roles of salt-resistant genes and fostering the cultivation of novel varieties through molecular biology in the future.

IAA-miR164a-NAC100L1 module mediates symbiotic incompatibility of cucumber/pumpkin grafted seedlings through regulating callose deposition

Grafting is one of the key technologies to overcome the obstacles of continuous cropping, and improve crop yield and quality. However, the symbiotic incompatibility between rootstock and scion affects the normal growth and development of grafted seedlings after survival. The specific molecular regulation mechanism of graft incompatibility is still largely unclear. In this study, we found that the IAA-miR164a-NAC100L1 module induced callose deposition to mediate the symbiotic incompatibility of cucumber/pumpkin grafted seedlings. The incompatible combination (IG) grafting interface accumulated more callose, and the activity of callose synthase (CmCalS1) and IAA content were significantly higher than in the compatible combination (CG). Treatment with IAA polar transport inhibitor in the root of the IG plants decreased CmCalS activity and callose content. Furthermore, IAA negatively regulated the expression of Cm-miR164a, which directly targeted cleavage of CmNAC100L1. Interestingly, CmNAC100L1 interacted with CmCalS1 to regulate its activity. Further analysis showed that the interaction between CmNAC100L1 and CmCalS1 increased the activity of CmCalS1 in the IG plants but decreased it in the CG plants. Point mutation analysis revealed that threonine at the 57th position of CmCalS1 protein played a critical role to maintain its enzyme activity in the incompatible rootstock. Thus, IAA inhibited the expression of Cm-miR164a to elevate the expression of CmNAC100L1, which promoted CmNAC100L1 interaction with CmCalS1 to enhance CmCalS1 activity, resulting in callose deposition and symbiotic incompatibility of cucumber/pumpkin grafted seedlings.

Exogenous Putrescine Modulates Nitrate Reductase-Dependent NO Production in Cucumber Seedlings Subjected to Salt Stress

Polyamines (PAs) are small aliphatic compounds that participate in the plant response to abiotic stresses. They also participate in nitric oxide (NO) production in plants; however, their role in this process remains unknown. Therefore, the study aimed to investigate the role of putrescine (Put) in NO production in the roots of cucumber seedlings subjected to salt stress (120 mM NaCl) for 1 and 24 h. In salinity, exogenous Put can regulate NO levels by managing NO biosynthesis pathways in a time-dependent manner. In cucumber roots exposed to 1 h of salinity, exogenous Put reduced NO level by decreasing nitrate reductase (NR)-dependent NO production and reduced nitric oxide synthase-like (NOS-like) activity. In contrast, during a 24 h salinity exposure, Put treatment boosted NO levels, counteracting the inhibitory effect of salinity on the NR and plasma membrane nitrate reductase (PM-NR) activity in cucumber roots. The role of endogenous Put in salt-induced NO generation was confirmed using Put biosynthesis inhibitors. Furthermore, the application of Put can modulate the NR activity at the genetic and post-translational levels. After 1 h of salt stress, exogenous Put upregulated CsNR1 and CsNR2 expression and downregulated CsNR3 expression. Put also decreased the NR activation state, indicating a reduction in the level of active dephosphorylated NR (dpNR) in the total enzyme pool. Conversely, in the roots of plants subjected to 24 h of salinity, exogenous Put enhanced the NR activation state, indicating an enhancement of the dpNR form in the total NR pool. These changes were accompanied by a modification of endogenous PA content. Application of exogenous Put led to an increase in the amount of Put in the roots and reduced endogenous spermine (Spm) content in cucumber roots under 24 h salinity. The regulatory role of exogenous Put on NO biosynthesis pathways may link with plant mechanisms of response to salt stress.

Interactions of Polyamines and Phytohormones in Plant Response to Abiotic Stress

Numerous environmental conditions negatively affect plant production. Abiotic stresses, such as salinity, drought, temperature, and heavy metals, cause damage at the physiological, biochemical, and molecular level, and limit plant growth, development, and survival. Studies have indicated that small amine compounds, polyamines (PAs), play a key role in plant tolerance to various abiotic stresses. Pharmacological and molecular studies, as well as research using genetic and transgenic approaches, have revealed the favorable effects of PAs on growth, ion homeostasis, water maintenance, photosynthesis, reactive oxygen species (ROS) accumulation, and antioxidant systems in many plant species under abiotic stress. PAs display a multitrack action: regulating the expression of stress response genes and the activity of ion channels; improving the stability of membranes, DNA, and other biomolecules; and interacting with signaling molecules and plant hormones. In recent years the number of reports indicating crosstalk between PAs and phytohormones in plant response to abiotic stresses has increased. Interestingly, some plant hormones, previously known as plant growth regulators, can also participate in plant response to abiotic stresses. Therefore, the main goal of this review is to summarize the most significant results that represent the interactions between PAs and plant hormones, such as abscisic acid, brassinosteroids, ethylene, jasmonates, and gibberellins, in plants under abiotic stress. The future perspectives for research focusing on the crosstalk between PAs and plant hormones were also discussed.

Versatile roles of polyamines in improving abiotic stress tolerance of plants

In recent years, extreme environmental cues such as abiotic stresses, including frequent droughts with irregular precipitation, salinity, metal contamination, and temperature fluctuations, have been escalating the damage to plants' optimal productivity worldwide. Therefore, yield maintenance under extreme events needs improvement in multiple mechanisms that can minimize the influence of abiotic stresses. Polyamines (PAs) are pivotally necessary for a defensive purpose under adverse abiotic conditions, but their molecular interplay in this remains speculative. The PAs' accretion is one of the most notable metabolic responses of plants under stress challenges. Recent studies reported the beneficial roles of PAs in plant development, including metabolic and physiological processes, unveiling their potential for inducing tolerance against adverse conditions. This review presents an overview of research about the most illustrious and remarkable achievements in strengthening plant tolerance to drought, salt, and temperature stresses by the exogenous application of PAs. The knowledge of underlying processes associated with stress tolerance and PA signaling pathways was also summarized, focusing on up-to-date evidence regarding the metabolic and physiological role of PAs with exogenous applications that protect plants under unfavorable climatic conditions. Conclusively, the literature proposes that PAs impart an imperative role in abiotic stress tolerance in plants. This implies potentially important feedback on PAs and plants' stress tolerance under unfavorable cues.

WRKY41/WRKY46-miR396b-5p-TPR module mediates abscisic acid-induced cold tolerance of grafted cucumber seedlings

Grafting is one of the key agronomic measures to enhance the tolerance to environmental stresses in horticultural plants, but the specific molecular regulation mechanism in this tolerance largely remains unclear. Here, we found that cucumber grafted onto figleaf gourd rootstock increased cold tolerance through abscisic acid (ABA) activating WRKY41/WRKY46-miR396b-5p-TPR (tetratricopeptide repeat-like superfamily protein) module. Cucumber seedlings grafted onto figleaf gourd increased cold tolerance and induced the expression of miR396b-5p. Furthermore, overexpression of cucumber miR396b-5p in Arabidopsis improved cold tolerance. 5' RNA ligase-mediated rapid amplification of cDNA ends (5' RLM-RACE) and transient transformation experiments demonstrated that TPR was the target gene of miR396b-5p, while TPR overexpression plants were hypersensitive to cold stress. The yeast one-hybrid and dual-luciferase assays showed that both WRKY41 and WRKY46 bound to MIR396b-5p promoter to induce its expression. Furthermore, cold stress enhanced the content of ABA in the roots and leaves of figleaf gourd grafted cucumber seedlings. Exogenous application of ABA induced the expression of WRKY41 and WRKY46, and cold tolerance of grafted cucumber seedlings. However, figleaf gourd rootstock-induced cold tolerance was compromised when plants were pretreated with ABA biosynthesis inhibitor. Thus, ABA mediated figleaf gourd grafting-induced cold tolerance of cucumber seedlings through activating the WRKY41/WRKY46-miR396b-5p-TPR module.

CsbZIP2-miR9748-CsNPF4.4 Module Mediates High Temperature Tolerance of Cucumber Through Jasmonic Acid Pathway

High temperature stress seriously affects the growth of cucumber seedlings, and even leads to a decline in yield and quality. miRNAs have been shown to be involved in regulating the response to stress in plants, but little is known about its effects on cucumber high temperature stress tolerance. Here, we found that high temperature stress induced the expression of miR9748 in cucumber. Overexpression of cucumber miR9748 in Arabidopsis improved high temperature tolerance. Transcriptome analysis revealed that miR9748 might mediate high temperature tolerance through plant hormone signal pathway. 5' RNA ligase-mediated rapid amplification of cDNA ends (5' RLM-RACE) and transient transformation technology demonstrated that CsNPF4.4 was the target gene of miR9748. CsNPF4.4 overexpression plants decreased high temperature tolerance accompanied by reducing the content of jasmonic acid (JA), but alleviated by foliar application of methyl jasmonate, indicating that CsNPF4.4 negatively regulated high temperature stress tolerance through inhibition JA signal pathway. Furthermore, high temperature stress also increased the expression level of CsbZIP2. Yeast one-hybrid and dual-luciferase assays showed that CsbZIP2 directly bound to the promoter of MIR9748 to induce its expression. Taken together, our results indicated that CsbZIP2 directly regulated miR9748 expression to cleave CsNPF4.4 to mediate high temperature tolerance through JA pathway.

Gibberellins regulate lateral root development that is associated with auxin and cell wall metabolisms in cucumber

Cucumber is an economically important crop cultivated worldwide. Gibberellins (GAs) play important roles in the development of lateral roots (LRs), which are critical for plant stress tolerance and productivity. Therefore, it is of great importance for cucumber production to study the role of GAs in LR development. Here, the results showed that GAs regulated cucumber LR development in a concentration-dependent manner. Treatment with 1, 10, 50 and 100 μM GA₃ significantly increased secondary root length, tertiary root number and length. Of these, 50 μM GA₃ treatment had strong effects on increasing root dry weight and the root/shoot dry weight ratio. Pairwise comparisons identified 417 down-regulated genes enriched for GA metabolism-related processes and 447 up-regulated genes enriched for cell wall metabolism-related processes in GA₃-treated roots. A total of 3523 non-redundant DEGs were identified in our RNA-Seq data through pairwise comparisons and linear factorial modeling. Of these, most of the genes involved in auxin and cell wall metabolisms were up-regulated in GA₃-treated roots. Our findings not only shed light on LR regulation mediated by GA but also offer an important resource for functional studies of candidate genes putatively involved in the regulation of LR development in cucumber and other crops.

Climate change regulated abiotic stress mechanisms in plants: a comprehensive review

Global climate change is identified as a major threat to survival of natural ecosystems. Climate change is a dynamic, multifaceted system of alterations in environmental conditions that affect abiotic and biotic components of the world. It results in alteration in environmental conditions such as heat waves, intensity of rainfall, CO₂ concentration and temperature that lead to rise in new pests, weeds and pathogens. Climate change is one of the major constraints limiting plant growth and development worldwide. It impairs growth, disturbs photosynthesis, and reduces physiological responses in plants. The variations in global climate have gained the attention of researchers worldwide, as these changes negatively affect the agriculture by reducing crop productivity and food security. With this background, this review focuses on the effects of elevated atmospheric CO₂ concentration, temperature, drought and salinity on the morphology, physiology and biochemistry of plants. Furthermore, this paper outlines an overview on the reactive oxygen species (ROS) production and their impact on the biochemical and molecular status of plants with increased climatic variations. Also additionally, different tolerance strategies adopted by plants to combat environmental adversities have been discussed.

Auxin is involved in arbuscular mycorrhizal fungi-promoted tomato growth and NADP-malic enzymes expression in continuous cropping substrates

BACKGROUND

Despite significant limitations of growth medium reuse, a large amount of organic substrate is reused in soilless cultivation of horticultural crops in China. Arbuscular mycorrhizal fungi (AMF) can promote nutrient absorption and improve plant tolerance to biotic and abiotic stresses. However, the mechanisms governing the effects of AMF on crop growth in organic continuous cropping substrates have not been elucidated.

RESULTS

In this study, we showed that the inoculation of AMF in continuous cropping substrates promoted growth and root development, and increased the root and NADP-malic enzyme (NADP-ME) activity of tomato seedlings. Root transcriptome analysis demonstrated that the plant hormone signal transduction pathway was highly enriched, and 109 genes that positively correlated with the AMF-inoculated plant phenotype were obtained by gene set enrichment analysis (GSEA), which identified 9 genes related to indole acetic acid (IAA). Importantly, the levels of endogenous IAA in tomato seedlings significantly increased after AMF inoculation. Furthermore, the application of AMF significantly increased the expression levels of NADP-ME1 and NADP-ME2, as well as the activity of NADP-ME, and enhanced the root activity of tomato seedlings in comparison to that observed without inoculation of AMF. However, these effects were blocked in plants treated with 2,3,5-triiodobenzoic acid (TIBA), a polar transport inhibitor of IAA.

CONCLUSIONS

These results suggest that IAA mediates the AMF-promoted tomato growth and expression of NADP-MEs in continuous cropping substrates. The study provides convincing evidence for the reuse of continuous cropping substrates by adding AMF as an amendment.