The multiple stress-responsive transcription factor SlNAC1 improves the chilling tolerance of tomato

An alternative 3' splice site of PeuHKT1;3 improves the response to salt stress through enhancing affinity to K+ in Populus

Alternative splicing (AS) serves as a crucial post-transcriptional regulator in plants that contributes to the resistance to salt stress. However, the underlying mechanism is largely unknown. In this research, we identified an important AS transcript in Populus euphratica, PeuHKT1:3a, generated by alternative 3' splice site splicing mode that resulted in the removal of 252 bases at the 5' end of the first exon in PeuHKT1:3. Protein sequence comparison showed that the site of AS occurred in PeuHKT1:3 is located at a crucial Ser residue within the first pore-loop domain, which leads to inefficient K+ transport in HKT I-type transporters. Expressing PeuHKT1;3a in an axt3 mutant yeast strain can effectively compensate for the lack of intracellular K+, whereas the expression of PeuHKT1;3 cannot yield the effect. Furthermore, in transgenic Arabidopsis and poplar plants, it was observed that lines expressing PeuHKT1;3a exhibited greater salt tolerance compared to those expressing the PeuHKT1;3 strain. Analysis of ion content and flux demonstrated that the transgenic PeuHKT1;3a line exhibited significantly higher K+ content compared to the PeuHKT1;3 line, while there was no significant difference in Na+ content. In conclusion, our findings revealed that AS can give rise to novel variants of HKT I-type proteins in P. euphratica with modified K+ selectivity to keep a higher K+/Na+ ratio to enhanced salt tolerance.

Chilling stress response in tobacco seedlings: insights from transcriptome, proteome, and phosphoproteome analyses

Tobacco (Nicotiana tabacum L.) is an important industrial crop, which is sensitive to chilling stress. Tobacco seedlings that have been subjected to chilling stress readily flower early, which seriously affects the yield and quality of their leaves. Currently, there has been progress in elucidating the molecular mechanisms by which tobacco responds to chilling stress. However, little is known about the phosphorylation that is mediated by chilling. In this study, the transcriptome, proteome and phosphoproteome were analyzed to elucidate the mechanisms of the responses of tobacco shoot and root to chilling stress (4 °C for 24 h). A total of 6,113 differentially expressed genes (DEGs), 153 differentially expressed proteins (DEPs) and 345 differential phosphopeptides were identified in the shoot, and the corresponding numbers in the root were 6,394, 212 and 404, respectively. This study showed that the tobacco seedlings to 24 h of chilling stress primarily responded to this phenomenon by altering their levels of phosphopeptide abundance. Kyoto Encyclopedia of Genes and Genomes analyses revealed that starch and sucrose metabolism and endocytosis were the common pathways in the shoot and root at these levels. In addition, the differential phosphopeptide corresponding proteins were also significantly enriched in the pathways of photosynthesis-antenna proteins and carbon fixation in photosynthetic organisms in the shoot and arginine and proline metabolism, peroxisome and RNA transport in the root. These results suggest that phosphoproteins in these pathways play important roles in the response to chilling stress. Moreover, kinases and transcription factors (TFs) that respond to chilling at the levels of phosphorylation are also crucial for resistance to chilling in tobacco seedlings. The phosphorylation or dephosphorylation of kinases, such as CDPKs and RLKs; and TFs, including VIP1-like, ABI5-like protein 2, TCP7-like, WRKY 6-like, MYC2-like and CAMTA7 among others, may play essential roles in the transduction of tobacco chilling signal and the transcriptional regulation of the genes that respond to chilling stress. Taken together, these findings provide new insights into the molecular mechanisms and regulatory networks of the responses of tobacco to chilling stress.

Characteristics of NAC transcription factors in Solanaceae crops and their roles in responding to abiotic and biotic stresses

As one of the largest transcription factor (TF) families in plants, the NAC (NAM, ATAF1/2, and CUC2) family plays important roles in response pathways to various abiotic and biotic stresses, such as drought, high salinity, low temperature, and pathogen infection. Although, there are a number of reviews on the involvement of NAC TF in plant responses to biotic and abiotic stresses, most of them are focused on the model plants Arabidopsis thaliana and Oryza sativa, and there is a lack of systematic evaluation of specific species. Solanaceae, the world's third most significant cash crop, has been seriously affected by environmental disturbances in recent years in terms of yield and quality, posing a severe threat to global food security. This review focuses on the functional roles of NAC transcription factors in response to external stresses involved in five important Solanaceae crops: tomato, potato, pepper, eggplant and tobacco, and analyzes the affinities between them. It will provide resources for stress-resistant breeding of Solanaceae crops using transgenic technology.

SlNAC3 suppresses cold tolerance in tomatoes by enhancing ethylene biosynthesis

Low temperature stress poses a significant challenge to the productivity of horticultural crops. The dynamic expression of cold-responsive genes plays a crucial role in plant cold tolerance. While NAC transcription factors have been extensively studied in plant growth and development, their involvement in regulating plant cold tolerance remains poorly understood. In this study, we focused on the identification and characterisation of SlNAC3 as the most rapid and robust responsive gene in tomato under low temperature conditions. Manipulating SlNAC3 through overexpression or silencing resulted in reduced or enhanced cold tolerance, respectively. Surprisingly, we discovered a negative correlation between the expression of CBF and cold tolerance in the SlNAC3 transgenic lines. These findings suggest that SlNAC3 regulates tomato cold tolerance likely through a CBF-independent pathway. Furthermore, we conducted additional investigations to identify the molecular mechanisms underlying SINAC3-mediated cold tolerance in tomatoes. Our results revealed that SlNAC3 controls the transcription of ethylene biosynthetic genes, thereby bursting ethylene release in response to cold stress. Indeed, the silencing of these genes led to an augmentation in cold tolerance. This discovery provides valuable insights into the regulatory pathways involved in ethylene-mediated cold tolerance in tomatoes, offering potential strategies for developing innovative approaches to enhance cold stress resilience in this economically important crop species.

NAC61 regulates late- and post-ripening osmotic, oxidative, and biotic stress responses in grapevine

During late- and post-ripening stages, grape berry undergoes profound biochemical and physiological changes whose molecular control is poorly understood. Here, we report the role of NAC61, a grapevine NAC transcription factor, in regulating different processes involved in berry ripening progression. NAC61 is highly expressed during post-harvest berry dehydration and its expression pattern is closely related to sugar concentration. The ectopic expression of NAC61 in Nicotiana benthamiana leaves resulted in low stomatal conductance, high leaf temperature, tissue collapse and a higher relative water content. Transcriptome analysis of grapevine leaves transiently overexpressing NAC61 and DNA affinity purification and sequencing analyses allowed us to narrow down a list of NAC61-regulated genes. Direct regulation of the stilbene synthase regulator MYB14, the osmotic stress-related gene DHN1b, the Botrytis cinerea susceptibility gene WRKY52, and NAC61 itself was validated. We also demonstrate that NAC61 interacts with NAC60, a proposed master regulator of grapevine organ maturation, in the activation of MYB14 and NAC61 expression. Overall, our findings establish NAC61 as a key player in a regulatory network that governs stilbenoid metabolism and osmotic, oxidative, and biotic stress responses that are the hallmark of late- and post-ripening grape stages.

Metabolomics combined with physiology and transcriptomics reveal how Nicotiana tabacum leaves respond to cold stress

Low temperature-induced cold stress is a major threat to plant growth, development and distribution. Unraveling the responses of temperature-sensitive crops to cold stress and the mechanisms of cold acclimation are critical for food demand. In this study, combined physiological, transcriptomic, and metabolomic analyses were conducted on Nicotiana tabacum suffering short-term 4 °C cold stress. Our results showed that cold stress destroyed cellular membrane stability, decreased the chlorophyll (Chl) and carotenoid contents, and closed stomata, resulting in lipid peroxidation and photosynthesis restriction. Chl fluorescence measurements revealed that primary photochemistry, photoelectrochemical quenching and photosynthetic electron transport in Nicotiana tabacum leaves were seriously suppressed upon exposer to cold stress. Enzymatic and nonenzymatic antioxidants, including superoxide dismutase, catalase, peroxidase, reduced glutathione, proline, and soluble sugar, were all profoundly increased to trigger the cold acclimation defense against oxidative damage. A total of 178 metabolites and 16,204 genes were differentially expressed in cold-stressed Nicotiana tabacum leaves. MEturquoise and MEblue modules identified by WGCNA were highly correlated with physiological indices, and the corresponding hub genes were significantly enriched in pathways related to photosynthesis - antenna proteins and flavonoid biosynthesis. Untargeted metabolomic analysis identified specific metabolites, including sucrose, phenylalanine, glutamine, glutamate, and proline, that enhance plant cold acclimation. Combined transcriptomics and metabolomic analysis highlight the vital roles of carbohydrate and amino acid metabolism in enhancing the cold tolerance of Nicotiana tabacum. Our comprehensive investigation provides novel insights for efforts to alleviate low temperature-induced oxidative damage to Nicotiana tabacum plants and proposes a breeding target for cold stress-tolerant cultivars.

CaSnRK2.4-mediated phosphorylation of CaNAC035 regulates abscisic acid synthesis in pepper (Capsicum annuum L.) responding to cold stress

Plant NAC transcription factors play a crucial role in enhancing cold stress tolerance, yet the precise molecular mechanisms underlying cold stress remain elusive. In this study, we identified and characterized CaNAC035, an NAC transcription factor isolated from pepper (Capsicum annuum) leaves. We observed that the expression of the CaNAC035 gene is induced by both cold and abscisic acid (ABA) treatments, and we elucidated its positive regulatory role in cold stress tolerance. Overexpression of CaNAC035 resulted in enhanced cold stress tolerance, while knockdown of CaNAC035 significantly reduced resistance to cold stress. Additionally, we discovered that CaSnRK2.4, a SnRK2 protein, plays an essential role in cold tolerance. In this study, we demonstrated that CaSnRK2.4 physically interacts with and phosphorylates CaNAC035 both in vitro and in vivo. Moreover, the expression of two ABA biosynthesis-related genes, CaAAO3 and CaNCED3, was significantly upregulated in the CaNAC035-overexpressing transgenic pepper lines. Yeast one-hybrid, Dual Luciferase, and electrophoretic mobility shift assays provided evidence that CaNAC035 binds to the promoter regions of both CaAAO3 and CaNCED3 in vivo and in vitro. Notably, treatment of transgenic pepper with 50 μm Fluridone (Flu) enhanced cold tolerance, while the exogenous application of ABA at a concentration of 10 μm noticeably reduced cold tolerance in the virus-induced gene silencing line. Overall, our findings highlight the involvement of CaNAC035 in the cold response of pepper and provide valuable insights into the molecular mechanisms underlying cold tolerance. These results offer promising prospects for molecular breeding strategies aimed at improving cold tolerance in pepper and other crops.

Banana MaNAC1 activates secondary cell wall cellulose biosynthesis to enhance chilling resistance in fruit

Chilling injury has a negative impact on the quantity and quality of crops, especially subtropical and tropical plants. The plant cell wall is not only the main source of biomass production, but also the first barrier to various stresses. Therefore, improving the understanding of the alterations in cell wall architecture is of great significance for both biomass production and stress adaptation. Herein, we demonstrated that the cell wall principal component cellulose accumulated during chilling stress, which was caused by the activation of MaCESA proteins. The sequence-multiple comparisons show that a cold-inducible NAC transcriptional factor MaNAC1, a homologue of Secondary Wall NAC transcription factors, has high sequence similarity with Arabidopsis SND3. An increase in cell wall thickness and cellulosic glucan content was observed in MaNAC1-overexpressing Arabidopsis lines, indicating that MaNAC1 participates in cellulose biosynthesis. Over-expression of MaNAC1 in Arabidopsis mutant snd3 restored the defective secondary growth of thinner cell walls and increased cellulosic glucan content. Furthermore, the activation of MaCESA7 and MaCESA6B cellulose biosynthesis genes can be directly induced by MaNAC1 through binding to SNBE motifs within their promoters, leading to enhanced cellulose content during low-temperature stress. Ultimately, tomato fruit showed greater cold resistance in MaNAC1 overexpression lines with thickened cell walls and increased cellulosic glucan content. Our findings revealed that MaNAC1 performs a vital role as a positive modulator in modulating cell wall cellulose metabolism within banana fruit under chilling stress.

SlMYB41 positively regulates tomato thermotolerance by activating the expression of SlHSP90.3

High-temperature stress has become a major abiotic factor that dramatically limits plant growth and crop yield. Plants have evolved complex mechanisms to cope with high-temperature stress, but the factors that regulate plant thermotolerance remain to be discovered. Here, a high temperature-induced MYB transcription factor SlMYB41 was cloned from tomato (Solanum lycopersicum). Two individual SlMYB41-RNA interference (RNAi) lines (MR) and one CRISPR/Cas9 mediated myb41 mutant (MC) were obtained to investigate the function of SlMYB41 in tomato thermotolerance. Under high-temperature stress, we found that the MR and MC lines showed more wilting than the wild type (WT), with more ion leakage, more MDA accumulation, lower contents of osmotic adjustment substances, and more accumulation of reactive oxygen species (ROS) which was resulted from lower antioxidative enzyme activities. In addition, the photosynthetic capacity and complex of MR and MC lines were damaged more seriously than WT plants under high-temperature stress, mainly manifested in lower photosynthetic rate and Fv/Fm. Moreover, heat stress-related genes, such as SlHSP17.6, SlHSP17.7, and SlHSP90.3 were downregulated in MR and MC lines. Importantly, Y1H and LUC analysis indicated that SlMYB41 can directly activate the transcription of SlHSP90.3. Together, our study suggest that SlMYB41 positively regulates tomato thermotolerance by activating the expression of SlHSP90.3.

Transcriptomic and physiological analyses reveal changes in secondary metabolite and endogenous hormone in ginger (Zingiber officinale Rosc.) in response to postharvest chilling stress

Storing postharvest ginger at low temperatures can extend its shelf life, but can also lead to chilling injury, loss of flavor, and excessive water loss. To investigate the effects of chilling stress on ginger quality, morphological, physiological, and transcriptomic changes were examined after storage at 26 °C, 10 °C, and 2 °C for 24 h. Compared to 26 °C and 10 °C, storage at 2 °C significantly increased the concentrations of lignin, soluble sugar, flavonoids, and phenolics, as well as the accumulation of H2O2, O2-, and thiobarbituric acid reactive substances (TBARS). Additionally, chilling stress inhibited the levels of indoleacetic acid, while enhancing gibberellin, abscisic acid, and jasmonic acid, which may have increased postharvest ginger's adaptation to chilling. Storage at 10 °C decreased lignin concentration and oxidative damage, and induced less fluctuant changes in enzymes and hormones than storage at 2 °C. RNA-seq revealed that the number of differentially expressed genes (DEGs) increased with decreasing temperature. Functional enrichment analysis of the 523 DEGs that exhibited similar expression patterns between all treatments indicated that they were primarily enriched in phytohormone signaling, biosynthesis of secondary metabolites, and cold-associated MAPK signaling pathways. Key enzymes related to 6-gingerol and curcumin biosynthesis were downregulated at 2 °C, suggesting that cold storage may negatively impact ginger quality. Additionally, 2 °C activated the MKK4/5-MPK3/6-related protein kinase pathway, indicating that chilling may increase the risk of ginger pathogenesis.

MdbZIP74 negatively regulates osmotic tolerance and adaptability to moderate drought conditions of apple plants

Drought is the most prominent threat to global agricultural production. The basic leucine zipper (bZIP) family is related to the response to a series of abiotic stress. In this case, apple calli and the seedlings of MdbZIP74-RNAi transgenic lines were obtained. Under osmotic stress and moderate drought conditions, the content of malondialdehyde, relative water content and other stress-related assays were measured. MdbZIP74 was found to negatively regulate the osmotic tolerance of apple callus. The growth of MdbZIP74-RNAi calli enhanced resistance without significant production loss. The silencing of MdbZIP74 contributes to redox balance and the adaptability of apple seedlings to moderate drought conditions. Four related differentially expressed genes in the biosynthesis of cytokinin and catabolic pathway were identified through a transcriptome analysis of MdbZIP74-RNAi seedlings under moderate drought conditions. MdLOG8 was further identified as the target of MdbZIP74 involved in the drought adaptability of apple plants using a dual experiment. Further confirmation showed MdLOG8 was maintained in the MdbZIP74-RNAi seedlings presumably acting as the growth regulator to enhance drought adaptability. It was concluded that the correct regulation of cytokinin level under moderate drought conditions maintains the redox balance and avoids the situation of plants surviving with the minimal resources.

Genomics, Proteomics, and Metabolomics Approaches to Improve Abiotic Stress Tolerance in Tomato Plant

To explore changes in proteins and metabolites under stress circumstances, genomics, proteomics, and metabolomics methods are used. In-depth research over the previous ten years has gradually revealed the fundamental processes of plants' responses to environmental stress. Abiotic stresses, which include temperature extremes, water scarcity, and metal toxicity brought on by human activity and urbanization, are a major cause for concern, since they can result in unsustainable warming trends and drastically lower crop yields. Furthermore, there is an emerging reliance on agrochemicals. Stress is responsible for physiological transformations such as the formation of reactive oxygen, stomatal opening and closure, cytosolic calcium ion concentrations, metabolite profiles and their dynamic changes, expression of stress-responsive genes, activation of potassium channels, etc. Research regarding abiotic stresses is lacking because defense feedbacks to abiotic factors necessitate regulating the changes that activate multiple genes and pathways that are not properly explored. It is clear from the involvement of these genes that plant stress response and adaptation are complicated processes. Targeting the multigenicity of plant abiotic stress responses caused by genomic sequences, transcripts, protein organization and interactions, stress-specific and cellular transcriptome collections, and mutant screens can be the first step in an integrative approach. Therefore, in this review, we focused on the genomes, proteomics, and metabolomics of tomatoes under abiotic stress.

Functional Characterization of the CpNAC1 Promoter and Gene from Chimonanthus praecox in Arabidopsis

The NAC (NAM, ATAF, and CUC) gene family is one of the largest plant-specific transcription factor families. Its members have various biological functions that play important roles in regulating plant growth and development and in responding to biotic and abiotic stresses. However, their functions in woody plants are not fully understood. In this study, we isolated an NAC family member, the CpNAC1 promoter and gene, from wintersweet. CpNAC1 was localized to the nucleus and showed transcriptional activation activity. qRT-PCR analyses revealed that the gene was expressed in almost all tissues tested, with the highest levels found in mature leaves and flower buds. Moreover, its expression was induced by various abiotic stresses and ABA treatment. Its expression patterns were further confirmed in CpNAC1pro:GUS (β-glucuronidase) plants. Among all the transgenic lines, CpNAC1pro-D2 showed high GUS histochemical staining and activity in different tissues of Arabidopsis. Furthermore, its GUS activity significantly increased in response to various abiotic stresses and ABA treatment. This may be related to the stress-related cis-elements, such as ABRE and MYB, which clustered in the CpNAC1pro-D2 segment, suggesting that CpNAC1pro-D2 is the core segment that responds to abiotic stresses and ABA. In addition, CpNAC1-overexpressed Arabidopsis plants had weaker osmosis tolerance than the wild-type plants, demonstrating that CpNAC1 may negatively regulate the drought stress response in transgenic Arabidopsis. Our results provide a foundation for further analyses of NAC family genes in wintersweet, and they broaden our knowledge of the roles that NAC family genes may play in woody plants.

Manipulation of the transcription factor SlNAC1 for improved tolerance to abiotic stress in tomato

The tomato transcription factor SlNAC1 plays an important role in abiotic stress response and is fine-tuned at both transcriptional and posttranslational levels. The SlNAC1 gene is strongly induced by multiple abiotic stresses and the SlNAC1 protein is subjected to ubiquitin proteasome-mediated degradation. We found here that SlNAC1 possesses two distinct transactivation domains (TADs), TAD1 and TAD2. Significantly, the instability of SlNAC1 was attributed to the acidic amino acid-rich TAD1, in which the instability and transcriptional potential of TAD1 functionally overlapped; whereas the glutamine-rich TAD2 was stable and accounted for the abiotic stress signalling mediated by SlNAC1. Towards the goal of enhanced tolerance to abiotic stress in tomatoes, we manipulated SlNAC1 at both gene and protein levels: we generated a stable and functional SlNAC1 mutant SlNAC1^∆191-270 by removing TAD1 and further engineered it to be stress-controllable by fusing the corresponding cDNA with the abiotic stress-inducible promoter Pro_StNAC1 . Transgenic tomato plants expressing the Pro_StNAC1 ::SlNAC1^∆191-270 transgene did not display any undesired traits and exhibited enhanced tolerance to cold, drought and salt stresses. Taken together, our manipulation of the stress-related transcription factor via conditional expression of its derived stable and functional mutant provides a successful example for developing crops dynamically adapted to abiotic stress.

Bolstered plant tolerance to low temperatures by overexpressing NAC transcription factors: identification of critical variables by meta-analysis

The potential biotechnological application of NAC overexpression has been challenged by meta-analysis, establishing a correlation between the magnitudes of several physiological and biochemical parameters and the enhanced tolerance to cold. Overexpression of various NAC (NAM/ATAF/CUC) transcription factors in different plant systems was shown to confer enhanced tolerance to low temperatures by inducing both common and distinctive stress response pathways. However, lack of consensus on the type of parameters evaluated, their magnitudes, and direction of the responses complicates drawing general conclusions on the effects of NAC expression in plant physiology. We report herein a meta-analysis summarizing the most critical response variables used to study the effect of overexpressing NAC regulators on cold stress tolerance. We found that NAC overexpression affected all of the outcome parameters in stressed plants, and one response in control conditions. Transformed plants displayed an increase of at least 40% in positive responses, while negative outcomes were reduced by at least 30%. The most reported parameters included survival, electrolyte leakage, and malondialdehyde contents, whereas the most sensitive to the treatments were the F_v/F_m parameter, survival, and the activity of catalases. We also explored how different experimental arrangements affected the magnitudes of the responses. NAC-mediated improvements were best observed after severe stress episodes and during brief treatments (ranging from 5 to 24 h), especially in terms of antioxidant activities, accumulation of free proline, and parameters related to membrane integrity. Use of heterologous expression also favored several indicators of plant fitness. Our findings should help both basic and applied research on the influence of NAC expression on enhanced tolerance to cold.

The miR164a-NAM3 module confers cold tolerance by inducing ethylene production in tomato

Because of a high sensitivity to cold, both the yield and quality of tomato (Solanum lycopersicum L.) are severely restricted by cold stress. The NAC transcription factor (TF) family has been characterized as an important player in plant growth, development, and the stress response, but the role of NAC TFs in cold stress and their interaction with other post-transcriptional regulators such as microRNAs in cold tolerance remains elusive. Here, we demonstrated that SlNAM3, the predicted target of Sl-miR164a/b-5p, improved cold tolerance as indicated by a higher maximum quantum efficiency of photosystem II (Fv/Fm), lower relative electrolyte leakage, and less wilting in SlNAM3-overexpression plants compared to wild-type. Further genetic and molecular confirmation revealed that Sl-miR164a/b-5p functioned upstream of SlNAM3 by inhibiting the expression of the latter, thus playing a negative role in cold tolerance. Interestingly, this role is partially mediated by an ethylene-dependent pathway because either Sl-miR164a/b-5p silencing or SlNAM3 overexpression improved cold tolerance in the transgenic lines by promoting ethylene production. Moreover, silencing of the ethylene synthesis genes, SlACS1A, SlACS1B, SlACO1, and SlACO4, resulted in a significant decrease in cold tolerance. Further experiments demonstrated that NAM3 activates SlACS1A, SlACS1B, SlACO1, and SlACO4 transcription by directly binding to their promoters. Taken together, the present study identified the miR164a-NAM3 module conferring cold tolerance in tomato plants via the direct regulation of SlACS1A, SlACS1B, SlACO1, and SlACO4 expression to induce ethylene synthesis.

Exogenous Zeaxanthin Alleviates Low Temperature Combined with Low Light Induced Photosynthesis Inhibition and Oxidative Stress in Pepper (Capsicum annuum L.) Plants

Low temperature combined with low light (LL) affects crop production, especially the yield and quality of peppers, in northwest China during the winter and spring seasons. Zeaxanthin (Z) is a known lipid protectant and active oxygen scavenger. However, whether exogenous Z can mitigate LL-induced inhibition of photosynthesis and oxidative stress in peppers remains unclear. In this study, we investigated the effects of exogenous Z on photosynthesis and the antioxidant machinery of pepper seedlings subject to LL stress. The results showed that the growth and photosynthesis of pepper seedlings were significantly inhibited by LL stress. In addition, the antioxidant machinery was disturbed by the uneven production and elimination of reactive oxygen species (ROS), which resulted in damage to the pepper. For example, membrane lipid peroxidation increased ROS content, and so on. However, exogenous application of Z before LL stress significantly increased the plant height, stem diameter, net photosynthetic rate (Pn), and stomata, which were obviously closed at LL. The activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), mono de-hydroascorbate reductase (MDHAR), de-hydroascorbate reductase (DHAR), ascorbate peroxidase (APX), and ascorbate oxidase (AAO) improved significantly due to the increased expression of CaSOD, CaCAT, CaAPX, CaMDHAR, and CaDHAR. The ascorbic (AsA) and glutathione (GSH) contents and ascorbic/dehydroascorbate (AsA/DHA) and glutathione/oxidized glutathione (GSH/GSSG) ratios also increased significantly, resulting in the effective removal of hydrogen peroxide (H2O2) and superoxide anions (O2•−) caused by LL stress. Thus, pre-treatment with Z significantly reduced ROS accumulation in pepper seedlings under LL stress by enhancing the activity of antioxidant enzymes and accumulation of components of the ascorbate–glutathione (AsA–GSH) cycle and upregulated key genes in the AsA–GSH cycle.

Strawberry FaSnRK1α Regulates Anaerobic Respiratory Metabolism under Waterlogging

Sucrose nonfermenting-1-related protein kinase 1 (SnRK1) is a central integrator of plant stress and energy starvation signalling pathways. We found that the FaSnRK1α-overexpression (OE) roots had a higher respiratory rate and tolerance to waterlogging than the FaSnRK1α-RNAi roots, suggesting that FaSnRK1α plays a positive role in the regulation of anaerobic respiration under waterlogging. FaSnRK1α upregulated the activity of anaerobic respiration-related enzymes including hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), pyruvate decarboxylase (PDC), alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH). FaSnRK1α also enhanced the ability to quench reactive oxygen species (ROS) by increasing antioxidant enzyme activities. We sequenced the transcriptomes of the roots of both wild-type (WT) and FaSnRK1α-RNAi plants, and the differentially expressed genes (DEGs) were clearly enriched in the defence response, response to biotic stimuli, and cellular carbohydrate metabolic process. In addition, 42 genes involved in glycolysis and 30 genes involved in pyruvate metabolism were significantly regulated in FaSnRK1α-RNAi roots. We analysed the transcript levels of two anoxia-related genes and three ERFVIIs, and the results showed that FaADH1, FaPDC1, FaHRE2 and FaRAP2.12 were upregulated in response to FaSnRK1α, indicating that FaSnRK1α may be involved in the ethylene signalling pathway to improve waterlogging tolerance. In conclusion, FaSnRK1α increases the expression of ERFVIIs and further activates anoxia response genes, thereby enhancing anaerobic respiration metabolism in response to low-oxygen conditions during waterlogging.

Dynamic Responses of Antioxidant and Glyoxalase Systems to Seed Aging Based on Full-Length Transcriptome in Oat (Avena sativa L.)

Seed aging is a major challenge for food security, agronomic production, and germplasm conservation, and reactive oxygen species (ROS) and methylglyoxal (MG) are highly involved in the aging process. However, the regulatory mechanisms controlling the abundance of ROS and MG are not well characterized. To characterize dynamic response of antioxidant and glyoxalase systems during seed aging, oat (Avena sativa L.) aged seeds with a range of germination percentages were used to explore physiological parameters, biochemical parameters and relevant gene expression. A reference transcriptome based on PacBio sequencing generated 67,184 non-redundant full-length transcripts, with 59,050 annotated. Subsequently, eleven seed samples were used to investigate the dynamic response of respiration, ROS and MG accumulation, antioxidant enzymes and glyoxalase activity, and associated genes expression. The 48 indicators with high correlation coefficients were divided into six major response patterns, and were used for placing eleven seed samples into four groups, i.e., non-aged (Group N), higher vigor (Group H), medium vigor (Group M), and lower vigor (Group L). Finally, we proposed a putative model for aging response and self-detoxification mechanisms based on the four groups representing different aging levels. In addition, the outcomes of the study suggested the dysfunction of antioxidant and glyoxalase system, and the accumulation of ROS and MG definitely contribute to oat seed aging.

SbbHLH85, a bHLH member, modulates resilience to salt stress by regulating root hair growth in sorghum

bHLH family proteins play an important role in plant stress response. However, the molecular mechanism regulating the salt response of bHLH is largely unknown. This study aimed to investigate the function and regulating mechanism of the sweet sorghum SbbHLH85 during salt stress. The results showed that SbbHLH85 was different from its homologs in other species. Also, it was a new atypical bHLH transcription factor and a key gene for root development in sweet sorghum. The overexpression of SbbHLH85 resulted in significantly increased number and length of root hairs via ABA and auxin signaling pathways, increasing the absorption of Na⁺. Thus, SbbHLH85 plays a negative regulatory role in the salt tolerance of sorghum. We identified a potential interaction partner of SbbHLH85, which was phosphate transporter chaperone PHF1 and modulated the distribution of phosphate, through screening a yeast two-hybrid library. Both yeast two-hybrid and BiFC experiments confirmed the interaction between SbbHLH85 and PHF1. The overexpression of SbbHLH85 led to a decrease in the expression of PHF1 as well as the content of Pi. Based on these results, we suggested that the increase in the Na⁺ content and the decrease in the Pi content resulted in the salt sensitivity of transgenic sorghum.

NAC-mediated membrane lipid remodeling negatively regulates fruit cold tolerance

Low temperatures are known to destroy cell membranes' structural integrity by affecting the remodeling of their phospholipids. Fruits stored at low temperature are prone to chilling injury, characterized by discoloration, absence of ripening, surface pitting, growth inhibition, flavor loss, decay, and wilting. Phosphatidic acid, a vital second-messenger lipid in plants, is known to accumulate in response to different kinds of stress stimuli. However, the regulatory mechanism of its production from the degradation of phospholipids remains poorly understood. We identified two cold-responsive NAC (NAM/ATAF1/CUC2) transcription factors from bananas, namely, MaNAC25 and MaNAC28, which negatively regulated cold tolerance in banana fruits by upregulating the expression of phospholipid degradation genes in banana fruits. Furthermore, MaNAC25 and MaNAC28 formed a positive feedback loop to induce phospholipid degradation and produce phosphatidic acid. In contrast, ethylene directly inhibited the degradation of phospholipids in banana and transgenic tomato fruits. In addition, ethylene reduced the activity of MaNAC25 and MaNAC28, thereby inhibiting phospholipid degradation. To conclude, NAC-mediated membrane lipid remodeling negatively regulates the cold tolerance of banana and transgenic tomato fruits.

Transcriptome-Based Identification and Functional Characterization of NAC Transcription Factors Responsive to Drought Stress in Capsicum annuum L

Capsicum annuum L. is one of the most cultivated Solanaceae species, and in the open field, water limitation leading to drought stress affects its fruit quality, fruit setting, fruit size and ultimately yield. We identified stage-specific and a common core set of differentially expressed genes, following RNA-seq transcriptome analyses of a breeding line subjected to acute drought stress followed by recovery (rewatering), at three stages of plant development. Among them, two NAC transcription factor (TF) genes, i.e., CaNAC072 and CaNAC104, were always upregulated after drought stress and downregulated after recovery. The two TF proteins were observed to be localized in the nucleus following their transient expression in Nicotiana benthamiana leaves. The expression of the two NACs was also induced by NaCl, polyethylene glycol (PEG) and abscisic acid (ABA) treatments, suggesting that CaNAC072 is an early, while CaNAC104 is a late abiotic stress-responsive gene. Virus-induced gene silencing (VIGS) of CaNAC104 did not affect the pepper plantlet’s tolerance to drought stress, while VIGS of CaNAC072 increased drought tolerance. Heterologous expression of CaNAC072 in Arabidopsis thaliana as well as in plants mutated for its homolog ANAC072 did not increase drought stress tolerance. This highlights a different role of the two NAC homologs in the two species. Here, we discuss the complex role of NACs as transcriptional switches in the response to drought stress in bell pepper.

De Novo Transcriptome Assembly, Functional Annotation, and Transcriptome Dynamics Analyses Reveal Stress Tolerance Genes in Mangrove Tree (Bruguiera gymnorhiza)

Their high adaptability to difficult coastal conditions makes mangrove trees a valuable resource and an interesting model system for understanding the molecular mechanisms underlying stress tolerance and adaptation of plants to the stressful environmental conditions. In this study, we used RNA sequencing (RNA-Seq) for de novo assembling and characterizing the Bruguiera gymnorhiza (L.) Lamk leaf transcriptome. B. gymnorhiza is one of the most widely distributed mangrove species from the biggest family of mangroves; Rhizophoraceae. The de novo assembly was followed by functional annotations and identification of individual transcripts and gene families that are involved in abiotic stress response. We then compared the genome-wide expression profiles between two populations of B. gymnorhiza, growing under different levels of stress, in their natural habitats. One population living in high salinity environment, in the shore of the Pacific Ocean- Japan, and the other population living about one kilometre farther from the ocean, and next to the estuary of a river; in less saline and more brackish condition. Many genes involved in response to salt and osmotic stress, showed elevated expression levels in trees growing next to the ocean in high salinity condition. Validation of these genes may contribute to future salt-resistance research in mangroves and other woody plants. Furthermore, the sequences and transcriptome data provided in this study are valuable scientific resources for future comparative transcriptome research in plants growing under stressful conditions.

Strategies and Structure Feature of the Aboveground and Belowground Microbial Community Respond to Drought in Wild Rice (Oryza longistaminata)

BACKGROUND

Drought is global environmental stress that limits crop yields. Plant-associated microbiomes play a crucial role in determining plant fitness in response to drought, yet the fundamental mechanisms for maintaining microbial community stability under drought disturbances in wild rice are poorly understood. We make explicit comparisons of leaf, stem, root and rhizosphere microbiomes from the drought-tolerant wild rice (Oryza longistaminata) in response to drought stress.

RESULTS

We find that the response of the wild rice microbiome to drought was divided into aboveground-underground patterns. Drought reduced the leaf and stem microbial community diversity and networks stability, but not that of the roots and rhizospheres. Contrary to the aboveground microbial networks, the drought-negative response taxa exhibited much closer interconnections than the drought-positive response taxa and were the dominant network hubs of belowground co-occurrence networks, which may contribute to the stability of the belowground network. Notably, drought induces enrichment of Actinobacteria in belowground compartments, but not the aboveground compartment. Additionally, the rhizosphere microbiome exhibited a higher proportion of generalists and broader habitat niche breadth than the microbiome at other compartments, and drought enhanced the proportion of specialists in all compartments. Null model analysis revealed that both the aboveground and belowground-community were governed primarily by the stochastic assembly process, moreover, drought decreased 'dispersal limitation', and enhanced 'drift'.

CONCLUSIONS

Our results provide new insight into the different strategies and assembly mechanisms of the above and belowground microbial community in response to drought, including enrichment of taxonomic groups, and highlight the important role of the stochastic assembly process in shaping microbial community under drought stress.

Group-C/S1 bZIP heterodimers regulate MdIPT5b to negatively modulate drought tolerance in apple species

Cytokinins play a central role in delaying senescence, reducing oxidative damage and maintaining plant growth during drought. This study showed that the ectopic expression of ProRE-deleted MdIPT5b, a key enzyme involved in cytokinin metabolism, increased the drought tolerance of transgenic Malus domestica (apple) callus and Solanum lycopersicum (tomato) seedlings by maintaining cytokinin homeostasis, and thus maintaining redox balance. Under restricted watering regimes, the yields of transgenic tomato plants were enhanced. Heterodimers of C/S1 bZIP are involved in the cytokinin-mediated drought response. The heterodimers bind the ProRE of MdIPT5b promoter, thus directly suppressing gene transcription. Single C/S1 bZIP members could not independently function as suppressors. However, specific paired members (heterodimers of MdbZIP80 with MdbZIP2 or with MdbZIP39) effectively suppressed transcription. The α-helical structure is essential for the heterodimerization of C/S1 bZIP members and for synergistic transcriptional suppression. As negative regulators of drought tolerance, suppressing either MdbZIP2 or MdbZIP39 alone does not improve the expression of MdIPT5b and did not increase the drought tolerance of transgenic apple callus. However, this could be achieved when they were co-suppressed. The suppression of MdbZIP80 alone could improve MdIPT5b expression and increase the drought tolerance of transgenic apple callus. However, these effects were reversed in response to the cosuppression of MdbZIP80 and MdIPT5b. Similar results were also observed during delayed dark-induced senescence in apple leaves. In conclusion, the apple C/S1 bZIP network (involving MdbZIP2, MdbZIP39 and MdbZIP80) directly suppressed the expression of MdIPT5b, thus negatively modulating drought tolerance and dark-induced senescence in a functionally redundant manner.

The NAC side of the fruit: tuning of fruit development and maturation

Fruits and seeds resulting from fertilization of flowers, represent an incredible evolutionary advantage in angiosperms and have seen them become a critical element in our food supply.Many studies have been conducted to reveal how fruit matures while protecting growing seeds and ensuring their dispersal. As result, several transcription factors involved in fruit maturation and senescence have been isolated both in model and crop plants. These regulators modulate several cellular processes that occur during fruit ripening such as chlorophyll breakdown, tissue softening, carbohydrates and pigments accumulation.The NAC superfamily of transcription factors is known to be involved in almost all these aspects of fruit development and maturation. In this review, we summarise the current knowledge regarding NACs that modulate fruit ripening in model species (Arabidopsis thaliana and Solanum lycopersicum) and in crops of commercial interest (Oryza sativa, Malus domestica, Fragaria genus, Citrus sinensis and Musa acuminata).

Late blight in tomato: insights into the pathogenesis of the aggressive pathogen Phytophthora infestans and future research priorities

This review provides insights into the molecular interactions between Phytophthora infestans and tomato and highlights research gaps that need further attention. Late blight in tomato is caused by the oomycota hemibiotroph Phytophthora infestans, and this disease represents a global threat to tomato farming. The pathogen is cumbersome to control because of its fast-evolving nature, ability to overcome host resistance and inefficient natural resistance obtained from the available tomato germplasm. To achieve successful control over this pathogen, the molecular pathogenicity of P. infestans and key points of vulnerability in the host plant immune system must be understood. This review primarily focuses on efforts to better understand the molecular interaction between host pathogens from both perspectives, as well as the resistance genes, metabolomic changes, quantitative trait loci with potential for improvement in disease resistance and host genome manipulation via transgenic approaches, and it further identifies research gaps and provides suggestions for future research priorities.

Cytokinins as central regulators during plant growth and stress response

Cytokinins are a class of phytohormone that participate in the regulation of the plant growth, development, and stress response. In this review, the potential regulating mechanism during plant growth and stress response are discussed. Cytokinins are a class of phytohormone that participate in the regulation of plant growth, physiological activities, and yield. Cytokinins also play a key role in response to abiotic stresses, such as drought, salt and high or low temperature. Through the signal transduction pathway, cytokinins interact with various transcription factors via a series of phosphorylation cascades to regulate cytokinin-target gene expression. In this review, we systematically summarize the biosynthesis and metabolism of cytokinins, cytokinin signaling, and associated gene regulation, and highlight the function of cytokinins during plant development and resistance to abiotic stress. We also focus on the importance of crosstalk between cytokinins and other classes of phytohormones, including auxin, ethylene, strigolactone, and gibberellin. Our aim is to provide a comprehensive overview of recent findings on the mechanisms by which cytokinins act as central regulators of plant development and stress reactions, and highlight topics for future research.

Targeting salt stress coping mechanisms for stress tolerance in Brassica: A research perspective

Brassica genus comprises numerous cultivated brassica species with various economic importance. Salt stress is an overwhelming problem causing serious losses in Brassica species (e.g. B. napus, B. rapa, B. oleracea, B. juncea) growth and grain yield production by inducing ionic and ROS toxicity. Given that a significant variation exists in salt tolerance level in Brassica genus, Brassica species exhibited numerous salt tolerance mechanisms which were either overlooked or given less importance to improve and understand innate salt stress tolerance mechanism in Brassica species. In this review, we tried to highlight the importance and recent findings relating to some overlooked and potential mechanisms such as role of neurotransmitters, and role of cytosolic Ca²⁺ and ROS as signaling elements to enhance salt stress tolerance. Studies revealed that salt tolerant brassica species retained more K⁺ in leaf mesophyll which confers overall salinity tolerance in salt tolerance brassica species. Neurotransmitter such as melatonin, dopamiane and eATP regulates K⁺ and Ca²⁺ permeable ion channels and plays a very crucial role in ionic homeostasis under salinity stress in brassica. At the end, the numerous possible salt stress agronomic strategies were also discussed to mitigate the severity of the salt stress in Brassica species.

Overexpression of Pti4, Pti5, and Pti6 in tomato promote plant defense and fruit ripening

Pseudomonas syringae pv. tomato (Pst) is a pathogenic microorganism that causes bacterial speck disease and affects tomato yield and quality. Pto is a disease resistant gene for plant to recognize and defense against Pst. Pto interacts with Pti (Pto interacting) proteins, which include three transcription factors, Pti4, Pti5, Pti6, and they were thought to be downstream of Pto-mediated pathway to promote the expression of disease-related genes. In the present work, the overexpression plants of Pti4, Pti5 or Pti6 were obtained by Agrobacterium-mediated transformation in tomato. The Pti4/5/6-overexpressed lines indicated enhanced expression of pathogenesis-related genes and resistance to pathogenic bacteria Pst DC3000. Meanwhile, the transgenic plants showed that Pti4/5/6 function in ripening but performed no obvious adverse influence on flowering time, seed-setting rate, weight and soluble solids content of fruits. Furthermore, Pti-overexpressed fruits exhibited increased enzymatic activities of phenylalnine ammonialyase, catalase, peroxidase and decreased content of malondialdehyde. Additionally, cell-free and in vivo ubiquitination assay indicated that Pti4, Pti5 and Pti6 degraded by 26S proteasome which suggested that these Pti transcription regulators' functions could be regulated by ubiquitin-mediated post translational regulation in tomato.

NAC Transcription Factors as Positive or Negative Regulators during Ongoing Battle between Pathogens and Our Food Crops

The NAC (NAM, ATAF1/2, and CUC2) family of proteins is one of the largest plant-specific transcription factor (TF) families and its members play varied roles in plant growth, development, and stress responses. In recent years, NAC TFs have been demonstrated to participate in crop-pathogen interactions, as positive or negative regulators of the downstream defense-related genes. NAC TFs link signaling pathways between plant hormones, including salicylic acid (SA), jasmonic acid (JA), ethylene (ET), and abscisic acid (ABA), or other signals, such as reactive oxygen species (ROS), to regulate the resistance against pathogens. Remarkably, NAC TFs can also contribute to hypersensitive response and stomatal immunity or can be hijacked as virulence targets of pathogen effectors. Here, we review recent progress in understanding the structure, biological functions and signaling networks of NAC TFs in response to pathogens in several main food crops, such as rice, wheat, barley, and tomato, and explore the directions needed to further elucidate the function and mechanisms of these key signaling molecules.

SlSGRL, a tomato SGR-like protein, promotes chlorophyll degradation downstream of the ABA signaling pathway

Chlorophyll (chl) degradation plays a vital role during green plant growth and development, including nutrient metabolism, fruit and seed maturation, and phototoxic detoxification. STAY-GREEN (SGR) is a plant-specific regulator involved in chl degradation. Previous studies showed that SlSGR1 functioned in chl degradation and lycopene accumulation during fruit ripening of tomato (Solanum lycopersicum). However, little is known about SlSGR-LIKE (SlSGRL) gene, which is a homolog of SlSGR1. We cloned the SlSGRL gene and created transgenic tomato plants overexpressing (OE) SlSGRL. Expression analysis showed that SlSGRL was up-regulated by abscisic acid (ABA). Our data showed that SlSGRL-OE lines exhibited earlier leaf yellowing than wild-type (WT) lines under ABA treatment. Yeast two-hybrid (Y2H) assay revealed that SlSGRL interacted with pheophytin pheophorbide hydrolase (SlPPH) and light-harvesting complex a2 (SlLHCa2) to promote the chl degradation. Further analysis demonstrated that ABA-INSENSITIVE5 (SlABI5) and SlABI5-LIKE regulated SlSGRL expression by directly binding to the sequence (-611 to -582) of the SlSGRL promoter that included an ABRE cis-element. We proposed that SlSGRL, which was regulated by SlABI5/SlABI5-LIKE, mainly acted in ABA-induced chl degradation via interacting with SlPPH and SlLHCa2.

SlWHY2 interacts with SlRECA2 to maintain mitochondrial function under drought stress in tomato

Drought stress in plants leads to inhibition of photosynthesis and respiration, accumulation of reactive oxygen species (ROS), and reprogramming of gene expression. Here, we established that the tomato (Solanum lycopersicum) WHIRLY2 (SlWHY2) gene, which encodes a mitochondrial single-stranded DNA-binding protein, was significantly induced by drought stress. Under drought conditions, SlWHY2 RNAi plants showed more wilting and lower fresh weight, chlorophyll content, quantum yield of photosystem I (PSI; YI), and maximal photochemical efficiency of PSII (Fv/Fm) than the wild type (WT). Drought treatment also caused the SlWHY2 RNAi lines to accumulate more ROS than the WT, and the silenced lines had lower AOX (alternative oxidase) activity. As expected, the mitochondrial membrane potential (MMP) was less stable in the SlWHY2 RNAi lines. The expression levels of seven genes in the mitochondrial genome (SYCF15, NAD7, NAD4, COS2, COX1, COX2, and COX3) were decreased even more in the SlWHY2 RNAi lines than they were in the WT under drought stress. SlWHY2 interacted directly in vivo and in vitro with SlRECA2, a mitochondrial recombinase A that is important for mitochondrial DNA recombination and repair. These results suggest that SlWHY2 plays an essential role in maintaining mitochondrial function and enhancing drought tolerance in tomato.

TaMYB86B encodes a R2R3-type MYB transcription factor and enhances salt tolerance in wheat

The MYB transcription factor family is important for plant responses to abiotic stresses. In this study, we identified three wheat TaMYB86 genes encoding R2R3-type MYB transcription factors. Analyses of the phylogenetic relationships and gene structures of TaMYB86A, TaMYB86B, and TaMYB86D revealed considerable similarities in gene structures and the encoded amino acid sequences. Additionally, TaMYB86B was highly expressed in the roots, stems, and leaves, suggesting it is critical for regulating salt stress responses in wheat. Moreover, TaMYB86B expression was induced by NaCl, abscisic acid (ABA), methyl jasmonate (MeJA), gibberellin (GA), auxin and low temperature treatments. The TaMYB86B protein localized in the nucleus and exhibited transcriptional activation activity. Under salt stress, TaMYB86B-overexpressing plants had a higher biomass and potassium ion (K⁺) content, but lower MDA, H₂O₂, O₂^-., and sodium ion (Na⁺) contents, when compared with the wild-type plants. Quantitative real-time PCR results indicated that the overexpression of TaMYB86B improved the expression of many stress-related genes. These findings suggest that TaMYB86B influences the salt tolerance of wheat by regulating the ion homeostasis to maintain an appropriate osmotic balance and decrease ROS levels.

Pentatricopeptide repeat protein PHOTOSYSTEM I BIOGENESIS FACTOR2 is required for splicing of ycf3

To gain a better understanding of the molecular mechanisms of photosystem I (PSI) biogenesis, we characterized the Arabidopsis thaliana photosystem I biogenesis factor 2 (pbf2) mutant, which lacks PSI complex. PBF2 encodes a P-class pentatricopeptide repeat (PPR) protein. In the pbf2 mutants, we observed a striking decrease in the transcript level of only one gene, the chloroplast gene ycf3, which is essential for PSI assembly. Further analysis of ycf3 transcripts showed that PBF2 is specifically required for the splicing of ycf3 intron 1. Computational prediction of binding sequences and electrophoretic mobility shift assays reveal that PBF2 specifically binds to a sequence in ycf3 intron 1. Moreover, we found that PBF2 interacted with two general factors for group II intron splicing CHLOROPLAST RNA SPLICING2-ASSOCIATED FACTOR1 (CAF1) and CAF2, and facilitated the association of these two factors with ycf3 intron 1. Our results suggest that PBF2 is specifically required for the splicing of ycf3 intron 1 through cooperating with CAF1 and CAF2. Our results also suggest that additional proteins are required to contribute to the specificity of CAF-dependent group II intron splicing.

The role of NAC transcription factor in plant cold response

The NAC transcription factor (TF) is one of the largest families of TFs in plants and plays an important role in plant growth, development, and response to environmental stress. The structural and functional characteristics of NAC TFs have been uncovered in the past years, including sequence binding features of the DNA-binding domain located in the N-terminus and dynamic interplay between the domain located at the C-terminus and other proteins. Studies on NAC TF are increasing in number; these studies distinctly contribute to our understanding of the regulatory networks of NAC-mediated complex signaling and transcriptional reprogramming. Previous studies have indicated that NAC TFs are key regulators of the plant stress response. However, these studies have been for six years so far and mainly focused on drought and salt stress. There are relatively few reports about NAC TFs in plant cold signal pathway and no related reviews have been published. In this review article, we summarize the structural features of NAC TFs, the target genes, upstream regulators and interaction proteins of stress-responsive NAC TFs, and the roles NAC TFs play in plant cold stress signal pathway.

Overexpression of PpSnRK1α in tomato enhanced salt tolerance by regulating ABA signaling pathway and reactive oxygen metabolism

BACKGROUND

SNF-related Kinase 1 (SnRK1) is a key component of the cell signaling network. SnRK1 is known to respond to a wide variety of stresses, but its exact role in salt stress response and tolerance is still largely unknown.

RESULTS

In this study, we reported that overexpression of the gene encoding the α subunit of Prunus persica SnRK1 (PpSnRK1α) in tomato could improve salt stress tolerance. The increase in salt stress tolerance in PpSnRK1α-overexpressing plants was found to correlate with increased PpSnRK1α expression level and SnRK1 kinase activity. And PpSnRK1α overexpression lines exhibited a lower level of leaf damage as well as increased proline content and reduced malondialdehyde (MDA) compared with wild-type (WT) lines under salt stress. Furthermore, PpSnRK1α enhanced reactive oxygen species (ROS) metabolism by increasing the expression level of antioxidase genes and antioxidant enzyme activities. We further sequenced the transcriptomes of the WT and three PpSnRK1α overexpression lines using RNA-seq and identified about 1000 PpSnRK1α-regulated genes, including many antioxidant enzymes, and these genes were clearly enriched in the MAPK signaling pathway (plant), plant-pathogen interactions and plant hormone signaling transduction and can respond to stimuli, metabolic processes, and biological regulation. Furthermore, we identified the transcriptional levels of several salt stress-responsive genes, SlPP2C37, SlPYL4, SlPYL8, SlNAC022, SlNAC042, and SlSnRK2 family were altered significantly by PpSnRK1α, signifying that SnRK1α may be involved in the ABA signaling pathway to improve tomato salt tolerance. Overall, these findings provided new evidence for the underlying mechanism of SnRK1α conferment in plant salt tolerance phenotypes.

CONCLUSIONS

Our findings demonstrated that plant salt stress resistance can be affected by the regulation of the SnRK1α. Further molecular and genetic approaches will accelerate our knowledge of PpSnRK1α functions, and inform the genetic improvement of salt tolerance in tomato through genetic engineering and other related strategies.

Identification of Pepper CaSBP08 Gene in Defense Response Against Phytophthora capsici Infection

Little information is available on the role of Squamosa promoter binding protein (SBP)-box genes in pepper plants. This family of genes is known to have transcription characteristics specific to plants and to regulate plant growth, development, stress responses, and signal transduction. To investigate their specific effects in pepper (Capsicum annuum), we screened pepper SBP-box family genes (CaSBP genes) for Phytophthora capsici (P. capsici) resistance genes using virus-induced gene silencing. CaSBP08, CaSBP11, CaSBP12, and CaSBP13, which are associated with plant defense responses against P. capsici, were obtained from among fifteen identified CaSBP genes. The function of CaSBP08 was identified in pepper defense response against P. capsici infection in particular. CaSBP08 protein was localized to the nucleus. Silencing of CaSBP08 enhanced resistance to P. capsici infection. Following P. capsici inoculation, the malondialdehyde content, peroxidase activity, and disease index percentage of the CaSBP08-silenced plants decreased compared to the control. Additionally, the expression levels of other defense-related genes, especially those of CaBPR1 and CaSAR8.2, were more strongly induced in CaSBP08-silenced plants than in the control. However, CaSBP08 overexpression in Nicotiana benthamiana enhanced susceptibility to P. capsici infection. This work provides a foundation for the further research on the role of CaSBP genes in plant defense responses against P. capsici infection.

Overexpression of a Malus baccata NAC Transcription Factor Gene MbNAC25 Increases Cold and Salinity Tolerance in Arabidopsis

NAC (no apical meristem (NAM), Arabidopsis thaliana transcription activation factor (ATAF1/2) and cup shaped cotyledon (CUC2)) transcription factors play crucial roles in plant development and stress responses. Nevertheless, to date, only a few reports regarding stress-related NAC genes are available in Malus baccata (L.) Borkh. In this study, the transcription factor MbNAC25 in M. baccata was isolated as a member of the plant-specific NAC family that regulates stress responses. Expression of MbNAC25 was induced by abiotic stresses such as drought, cold, high salinity and heat. The ORF of MbNAC25 is 1122 bp, encodes 373 amino acids and subcellular localization showed that MbNAC25 protein was localized in the nucleus. In addition, MbNAC25 was highly expressed in new leaves and stems using real-time PCR. To analyze the function of MbNAC25 in plants, we generated transgenic Arabidopsis plants that overexpressed MbNAC25. Under low-temperature stress (4 °C) and high-salt stress (200 mM NaCl), plants overexpressing MbNAC25 enhanced tolerance against cold and drought salinity conferring a higher survival rate than that of wild-type (WT). Correspondingly, the chlorophyll content, proline content, the activities of antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were significantly increased, while malondialdehyde (MDA) content was lower. These results indicated that the overexpression of MbNAC25 in Arabidopsis plants improved the tolerance to cold and salinity stress via enhanced scavenging capability of reactive oxygen species (ROS).

The NAC transcription factor CaNAC064 is a regulator of cold stress tolerance in peppers

NAC (NAM, ATAF1/2 and CUC2) proteins are plant-specific transcription factors (TFs) that are important in plant abiotic stress responses. In this study we isolated a NAC gene from Capsicum annuum leaves, designated as CaNAC064. We characterized the amino acid sequence of CaNAC064 and found that it contain conserved domains of the NAC family, including a highly conserved N-terminus domain and a highly variable C-terminus domain. Expression analysis showed that the 4⁰C, 40⁰C, salicylic acid (SA) and abscisic acid (ABA) treatments strongly induced the expression of CaNAC064 through silencing of CaNAC064 in pepper and overexpressing in Arabidopsis. CaNAC064-silenced pepper plants exhibited more serious wilting, higher MDA contents and chilling injury index, lower proline content, and more accumulation of ROS in the leaves after cold stress. The CaNAC064-overexpressing Arabidopsis plants exhibited lower MDA content, chilling injury index and relative electrolyte leakage content as compared to WT plants under cold stress. Transcriptional activation activity analysis indicated that CaNAC064 has transcriptional activation activity in the 691-1071 bp key region. We identified 45 proteins that putatively interact with CaNAC064 using the Yeast Two-Hybrid method. According to the Yeast Two-Hybrid and BIFC results, CaNAC064 interacted with low temperature-induced haplo-proteinase proteins in plant cell. These results suggested that CaNAC064 positively modulates plant cold-tolerance, laying the foundation for future investigations into the role of NACs as regulatory proteins of cold tolerance in plants.

The Role of Major Transcription Factors in Solanaceous Food Crops under Different Stress Conditions: Current and Future Perspectives

Plant growth, development, and productivity are adversely affected by environmental stresses such as drought (osmotic stress), soil salinity, cold, oxidative stress, irradiation, and diverse diseases. These impacts are of increasing concern in light of climate change. Noticeably, plants have developed their adaptive mechanism to respond to environmental stresses by transcriptional activation of stress-responsive genes. Among the known transcription factors, DoF, WRKY, MYB, NAC, bZIP, ERF, ARF and HSF are those widely associated with abiotic and biotic stress response in plants. Genome-wide identification and characterization analyses of these transcription factors have been almost completed in major solanaceous food crops, emphasizing these transcription factor families which have much potential for the improvement of yield, stress tolerance, reducing marginal land and increase the water use efficiency of solanaceous crops in arid and semi-arid areas where plant demand more water. Most importantly, transcription factors are proteins that play a key role in improving crop yield under water-deficient areas and a place where the severity of pathogen is very high to withstand the ongoing climate change. Therefore, this review highlights the role of major transcription factors in solanaceous crops, current and future perspectives in improving the crop traits towards abiotic and biotic stress tolerance and beyond. We have tried to accentuate the importance of using genome editing molecular technologies like CRISPR/Cas9, Virus-induced gene silencing and some other methods to improve the plant potential in giving yield under unfavorable environmental conditions.

Molecular and Functional Characterization of CaNAC035, an NAC Transcription Factor From Pepper (Capsicum annuum L.)

NAC (NAM, ATAF1/2, and CUC2) proteins are the plant-specific transcription factors (TFs) which are important in plant response to abiotic stresses. However, knowledge about the functional role that NACs play in pepper abiotic stress tolerance is limited. In this study, we isolated a NAC TF gene, CaNAC035, from pepper (Capsicum annuum L.), where the protein is localized in the nucleus and functions as a transcriptional activator. CaNAC035 expression is induced by low and high temperatures, osmotic stress, salt, gibberellic acid (GA), methyl-jasmonic acid (MeJA), salicylic acid (SA), and abscisic acid (ABA). To understand the function of CaNAC035 in the abiotic stress responsep, we used virus-induced gene silencing in pepper to knockdown the CaNAC035 and overexpressed the CaNAC035 in Arabidopsis. The results showed that pepper seedlings in which CaNAC035 was silenced, showed more damage than the control pepper plants after cold, NaCl, and mannitol treatments. Correspondingly increased electrolyte leakage, a higher level of malondialdehyde (MDA), H₂O₂, and superoxide radicals were found after cold treatments. CaNAC035-silenced seedlings exhibited lower chlorophyll content while CaNAC035-overexpressed Arabidopsis plants had higher germination rate and fresh weight after mannitol and NaCl treatments. We also reported 18 proteins that potentially interact with CaNAC035 and may participate in processes such as the stress response, resistance, and photosynthesis. Our results suggest that CaNAC035 is a positive regulator of abiotic stress tolerance in pepper which acts through multiple signaling pathways.

A tomato transcription factor, SlDREB3 enhances the tolerance to chilling in transgenic tomato

The dehydration response factor (DREB) transcription factor (TF) family can function in response to multiple cues around environment in plants. Nevertheless, the functions of dehydration response factor (DREB protein) in plant cold tolerance, especially in tomatoes (Solanum lycopersicum), have been rarely studied. In this study, the functions of tomato DREB TF (SlDREB3) in cold resistance were studied using transgenic tomatoes. The level of transcripts revealed that SlDREB3 was triggered by H₂O₂ and 4 °C treatments, indicating that SlDREB3 participates in response to cold stress in plants. SlDREB3-overexpressing plants exhibited high fresh mass, chlorophyll content, Fv/Fm, and O₂-evolving activity; low membrane damage; and reactive oxygen species accumulation under chilling stress. Furthermore, the high expression levels of late embryogenesis-abundant genes SlLEA9 and SlLEA26 were detected in transgenic plants in response to cold stress. These findings revealed that SlDREB3 overexpression improved the tolerance to cold stress in transgenic plants possibly by upregulating SlLEAs expression.

A Novel Transcription Factor CaSBP12 Gene Negatively Regulates the Defense Response against Phytophthora capsici in Pepper (Capsicum annuum L.)

SBP-box (Squamosa-promoter binding protein) genes are a type of plant-specific transcription factor and play important roles in plant growth, signal transduction and stress response. However, little is known about the SBP-box genes in pepper (CaSBP), especially in the process of Phytophthora capsici infection. In this study, a novel gene (CaSBP12) was selected from the CaSBP gene family, which was isolated from the pepper genome database in our previous study. The CaSBP12 gene was located in the nucleus of the cell and its silencing in the pepper plant enhanced the defense response against Phytophthora capsici infection. After inoculation with Phytophthora capsici, the root activity of the CaSBP12-silenced plants is compared to control plants, while malondialdehyde (MDA) content is compared viceversa. Additionally, the expression of defense related genes (CaPO1, CaSAR8.2, CaBPR1, and CaDEF1) in the silenced plants were induced to different degrees and the peak of CaSAR8.2 and CaBPR1 were higher than that of CaDEF1. The CaSBP12 over-expressed Nicotiana benthamiana plants were more susceptible to Phytophthora capsici infection with higher EC (electrical conductivity) and MDA contents as compared to the wild-type. The relative expression of defense related genes (NbDEF, NbNPR1, NbPR1a, and NbPR1b) in transgenic and wild-type Nicotiana benthamiana plants were induced, especially the NbPR1a and NbPR1b. In conclusion, these results indicate that CaSBP12 gene negative regulates the defense response against Phytophthora capsici infection which suggests their potentially significant role in plant defense. To our knowledge, this is the first report on CaSBP gene which negative regulate defense response.

Over-expression of a protein disulfide isomerase gene from Methanothermobacter thermautotrophicus, enhances heat stress tolerance in rice

High temperature (HT) stress is a major environmental stress that limits agricultural production worldwide. Discovery and application of genes promoting high temperature tolerance is essential to enhance crop tolerance to heat stress. Proteins associated with chaperone and protein folding plays an important role in the high temperature stress response of plants. MTH1745 (MtPDI), a disulfide isomerase-like protein (PDI) with a chaperone function and disulfide isomerase activity from Methanothermobacter thermautotrophicus delta H, was selected for studying the heat stress tolerance using an ectopic expression method in rice. Through molecular identification via quantitative real-time PCR and western blot, we demonstrated that the MtPDI gene was expressed stably in transgenic rice. Heat stress tolerance and survival ratio were significantly improved in seedling transgenic rice. At the same time, proline content, superoxide dismutase (SOD) and peroxidase (POD) activities were increased in MtPDI transgenic rice with a reduced malondialdehyde (MDA) content. Moreover, increased content of thiols group was discovered in transgenic plants. These results indicate that heterologous expression of MtPDI from extremophiles could confer heat stress tolerance of transgenic rice through the accumulation of proline content, the synergistic increase of the antioxidant enzymes activity and elevated production of more thiols group, which finally ameliorated the oxidative damage.

Molecular and functional characterization of ShNAC1, an NAC transcription factor from Solanum habrochaites

NAC transcription factors (TFs) are important regulators of plant adaptation to abiotic stress. In this study, we functionally characterized an NAC TF, ShNAC1, from Solanum habrochaites. ShNAC1 was up-regulated by drought, cold, and salt stresses, and it displayed lower expression at the late stage of stress treatments than its orthologous gene in S. lycopersicum. Overexpression of ShNAC1 in tomato resulted in reduced cold, drought, and salt tolerance. Additionally, ShNAC1 displayed the highest expression in senescent leaf, and overexpressing ShNAC1 accelerated salt- and dark-induced leaf senescence. ShNAC1 was located in the nucleus without transactivation activity. RNA-seq analysis revealed that 81% (190 out of 234) differentially-expressed genes (DEGs) showed down-regulation in the transgenic line L2 compared with wild-type, suggesting that ShNAC1 may function as a transcriptional repressor. Among these down-regulated DEGs, many were involved in stress responses, such as SlHKT1;1, SlMAPKKK59, SlJA2, SlTIL, SlALDH2B1, etc. Noticeably, one ACS gene and three ACO genes involved in ethylene biosynthesis were up-regulated, while seven ERF genes in the ethylene signal transduction pathway were down-regulated in the transgenic lines, respectively. Our results suggested that ShNAC1 negatively regulates tolerance to abiotic stress in tomato probably by modulating the ethylene biosynthesis and signal transduction pathways.

Cold-regulated protein (SlCOR413IM1) confers chilling stress tolerance in tomato plants

Chilling stress severely affects the growth, development and productivity of crops. Chloroplast, a photosynthesis site, is extremely sensitive to chilling stress. In this study, the functions of a gene encoding a cold-regulated protein (SlCOR413IM1) under chilling stress were investigated using sense and antisense transgenic tomatoes. Under chilling stress, SlCOR413IM1 expression was rapidly induced and the sense lines exhibited better growth state of seedlings and grown tomato plants. Overexpression of SlCOR413IM1 alleviated chilling-induced damage to the chloroplast membrane and structure, whereas suppression of SlCOR413IM1 aggravated the damage to chloroplast. Moreover, the net photosynthetic rate (Pn), maximum photochemical efficiency of photosystem II (PSII) (Fv/Fm), actual photochemical efficiency of PSII (ΦPSII) and the activities of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and stromal fructose-1, 6-bisphosphatase (sFBPase) were higher in the sense lines than those in the antisense lines. Hence, the inhibition of photosynthetic capacity was less severe in the sense lines but more severe in the antisense lines compared with that in wild-type (WT) plants. Taken together, overexpression of SlCOR413IM1 enhanced the chilling stress tolerance, whereas suppression of this gene increased the chilling sensitivity of tomato plants.

Characterization of a Potential Ripening Regulator, SlNAC3, from Solanum Lycopersicum

NAC (for NAM, ATAF1-2, and CUC2) proteins are one of the largest transcription factor families in plants. They have various functions and are closely related to developmental processes of fruits. Tomato (Solanum lycopersicum) is a model plant for studies of fruit growth patterns. In this study, the functional characteristics and action mechanisms of a new NAC-type transcription factor, SlNAC3 (SGN-U568609), were examined to determine its role in tomato development and ripening. The SlNAC3 protein was produced by prokaryotic expression and used to immunize New Zealand white rabbits to obtain a specific polyclonal antibody against SlNAC3. By co-immunoprecipitation and MALDI-TOF-MS assays, we showed that there was an interaction between the SlNAC3 protein and Polygalacturonase-2 (PG-2), which is related to the ripening and softening of fruit. Chromatin immunoprecipitation assays revealed the genome of the highly stress-tolerant Solanum pennellii chromosome 10 (sequence ID, HG975449.1), further demonstrating that SlNAC3 is a negative regulator of drought and salinity stress resistance in tomato, consistent with previous reports. These results indicate that SlNAC3 is not only involved in abiotic stress, but also plays a necessary role in mediating tomato ripening.