Networks of transcription factors with roles in environmental stress response

Evolution of gene networks underlying adaptation to drought stress in the wild tomato Solanum chilense

Drought stress is a key limitation for plant growth and colonization of arid habitats. We study the evolution of gene expression response to drought stress in a wild tomato, Solanum chilense, naturally occurring in dry habitats in South America. We conduct a transcriptome analysis under standard and drought experimental conditions to identify drought-responsive gene networks and estimate the age of the involved genes. We identify two main regulatory networks corresponding to two typical drought-responsive strategies: cell cycle and fundamental metabolic processes. The metabolic network exhibits a more recent evolutionary origin and a more variable transcriptome response than the cell cycle network (with ancestral origin and higher conservation of the transcriptional response). We also integrate population genomics analyses to reveal positive selection signals acting at the genes of both networks, revealing that genes exhibiting selective sweeps of older age also exhibit greater connectivity in the networks. These findings suggest that adaptive changes first occur at core genes of drought response networks, driving significant network re-wiring, which likely underpins species divergence and further spread into drier habitats. Combining transcriptomics and population genomics approaches, we decipher the timing of gene network evolution for drought stress response in arid habitats.

Heat-stress-responsive HvHSFA2e gene regulates the heat and drought tolerance in barley through modulation of phytohormone and secondary metabolic pathways

KEY MESSAGE

The heat stress transcription factor HSFA2e regulates both temperature and drought response via hormonal and secondary metabolism alterations. High temperature and drought are the primary yield-limiting environmental constraints for staple food crops. Heat shock transcription factors (HSF) terminally regulate the plant abiotic stress responses to maintain growth and development under extreme environmental conditions. HSF genes of subclass A2 predominantly express under heat stress (HS) and activate the transcriptional cascade of defense-related genes. In this study, a highly heat-inducible HSF, HvHSFA2e was constitutively expressed in barley (Hordeum vulgare L.) to investigate its role in abiotic stress response and plant development. Transgenic barley plants displayed enhanced heat and drought tolerance in terms of increased chlorophyll content, improved membrane stability, reduced lipid peroxidation, and less accumulation of ROS in comparison to wild-type (WT) plants. Transcriptome analysis revealed that HvHSFA2e positively regulates the expression of abiotic stress-related genes encoding HSFs, HSPs, and enzymatic antioxidants, contributing to improved stress tolerance in transgenic plants. The major genes of ABA biosynthesis pathway, flavonoid, and terpene metabolism were also upregulated in transgenics. Our findings show that HvHSFA2e-mediated upregulation of heat-responsive genes, modulation in ABA and flavonoid biosynthesis pathways enhance drought and heat stress tolerance.

Regulatory mechanisms used by ZmMYB39 to enhance drought tolerance in maize (Zea mays) seedlings

Drought is a significant abiotic stressor that limits maize (Zea mays L.) growth and development. Thus, enhancing drought tolerance is critical for promoting maize production. Our findings demonstrated that ZmMYB39 is an MYB transcription factor with transcriptional activation activity. Drought stress experiments involving ZmMYB39 overexpression and knockout lines indicated that ZmMYB39 positively regulated drought stress tolerance in maize. DAP-Seq, EMSA, dual-LUC, and RT-qPCR provided initial insights into the molecular regulatory mechanisms by which ZmMYB39 enhances drought tolerance in maize. ZmMYB39 directly promoted the expression of ZmP5CS1, ZmPOX1, ZmSOD2, ZmRD22, ZmNAC49, and ZmDREB2A, which are involved in stress resistance. ZmMYB39 enhanced drought tolerance by interacting with and promoting the expression of ZmFNR1, ZmHSP20, and ZmDOF6. Our study offers a theoretical basis for understanding the molecular regulatory networks involved in maize drought stress response. Furthermore, ZmMYB39 serves as a valuable genetic resource for breeding drought-resistant maize.

Identification and expression of the Di19 gene family in response to abiotic stress in common bean (Phaseolus vulgaris L.)

Drought-induced 19 (Di19) protein plays critical biological functions in response to adversity as well as in plant growth and development. Exploring the role and mechanism of Di19 in abiotic stress responses is of great significance for improving plant tolerance. In this study, six Di19 genes were identified in the common bean (Phaseolus vulgaris L.), which were mainly derived from segmental duplications. These genes share conserved exon/intron structures and were classified into three subfamilies based on their phylogenetic relationships. The composition and arrangement of conserved motifs were consistent with their phylogenetic relationships. Many hormone- and stress-responsive elements were distributed in the promoters region of PvDi19 genes. Variations in histidine residues in the Cys2/His2 (C2H2) zinc-finger domains resulted in an atypical tertiary structure of PvDi19-5. Gene expression analysis showed rapid induction of PvDi19-1 in roots by 10% PEG treatment, and PvDi19-2 in leaves by 20% PEG treatment, respectively. Most PvDi19s exhibited insensitivity to saline-alkali stress, except for PvDi19-6, which was notably induced during later stages of treatment. The most common bean Di19 genes were inhibited or not regulated by cadmium stress, but the expression of PvDi19-6 in roots was significantly upregulated when subjected to lower concentrations of cadmium (5 mmol). Moreover, Di19s exhibited greater sensitivity to severe cold stress (6°C). These findings enhance our understanding of the role of PvDi19s in common bean abiotic stress responses and provide a basis for future genetic enhancements in common bean stress tolerance.

The 14-3-3 protein GRF8 modulates salt stress tolerance in apple via the WRKY18-SOS pathway

Salinity is a severe abiotic stress that limits plant survival, growth, and development. 14-3-3 proteins are phosphopeptide-binding proteins that are involved in numerous signaling pathways, such as metabolism, development, and stress responses. However, their roles in salt tolerance are unclear in woody plants. Here, we characterized an apple (Malus domestica) 14-3-3 gene, GENERAL REGULATORY FACTOR 8 (MdGRF8), the product of which promotes salinity tolerance. MdGRF8 overexpression improved salt tolerance in apple plants, whereas MdGRF8-RNA interference (RNAi) weakened it. Yeast 2-hybrid, bimolecular fluorescence complementation, pull-down, and coimmunoprecipitation assays revealed that MdGRF8 interacts with the transcription factor MdWRKY18. As with MdGRF8, overexpressing MdWRKY18 enhanced salt tolerance in apple plants, whereas silencing MdWRKY18 had the opposite effect. We also determined that MdWRKY18 binds to the promoters of the salt-related genes SALT OVERLY SENSITIVE 2 (MdSOS2) and MdSOS3. Moreover, we showed that the 14-3-3 protein MdGRF8 binds to the phosphorylated form of MdWRKY18, enhancing its stability and transcriptional activation activity. Our findings reveal a regulatory mechanism by the MdGRF8-MdWRKY18 module for promoting the salinity stress response in apple.

Genome-wide identification of PYL/PYR-PP2C (A)-SnRK2 genes in Eutrema and their co-expression analysis in response to ABA and abiotic stresses

ABA signaling core components PYR/PYL, group A PP2C and SnRK2 play important roles in various environmental stress responses of plants. This study identified 14 PYR/PYL, 9 PP2C (A), and 10 SnRK2 genes from halophytic Eutrema. Phylogenetic analysis showed 4 EsPYR/PYL, 4 EsPP2C (A) and 3 EsSnRK2 subfamilies characterized, which was supported by their gene structures and protein motifs. Large-scale segmental duplication event was demonstrated to be a major contributor to expansion of the EsPYL-PP2C (A)-SnRK2 gene families. Synteny relationship analysis revealed more orthologous PYL-PP2C (A)-SnRK2 gene pairs located in collinear blocks between Eutrema and Brassica than that between Eutrema and Arabidopsis. RNA-seq and qRT-PCR revealed EsABI1, EsABI2 and EsHAL2 showed a significantly up-regulated expression in leaves and roots in response to ABA, NaCl or cold stress. Three markedly co-expression modules of ABA/R-brown, NaCl/L-lightsteelblue1 and Cold/R-lightgreen were uncovered to contain EsPYL-PP2C (A)-SnRK2 genes by WGCNA analysis. GO and KEGG analysis indicated that the genes of ABA/R-brown module containing EsHAB1, EsHAI2 and EsSnRK2.6 were enriched in proteasome pathway. Further, EsHAI2-OE transgenic Arabidopsis lines showed significantly enhanced seeds germination and seedlings growth. This work provides a new insight for elucidating potential molecular functions of PYL-PP2C (A)-SnRK2 responding to ABA and abiotic stresses.

The role of economic growth, information technologies, and globalization in achieving environmental quality: a novel framework for selected Asian countries

This study examines the impact of information and communication technologies (ICT), GDP growth, population, and globalization on the environmental quality of 31 Asian economies (i.e., categorized as lower middle-income, upper middle-income, and high-income groups Asian economies). This analysis employed the time series data from 1990 to 2018. The robust second-generation econometric technologies are used in this analysis. This study applied the Environmental Kuznets curve (EKC) premises under the extended "STIRPAT model" to add population and GDP (per capita) and information technologies (ICTs) by employing ecological footprint. To estimate, the estimators of this study used the CS-ARDL estimates, and for robustness check, this study used the augmented mean group (AMG) test. The co-integration test found the long-run association between ecological footprint and its main determinants. The results of CS-ARDL have confirmed the imperative role of information technologies in mitigating the ecological footprint in the higher, upper-middle, and lower-middle-income economies of Asian economies. The statistical findings of this study are robust to diagnostic tests and alternative estimation proxies and techniques. Moreover, policymakers need to identify the direction of the information technology-ecological footprint nexus through cooperation in combating climate change with financial assistance in the ICT sector.

Over-expression of DREB46 enhances drought tolerance in Populus trichocarpa

The drought responsive element binding (DREB) gene family has a significant role in plant abiotic stress responses. Here, we cloned a drought-inducible DREB gene, DREB46 (Potri.019G075500), and investigated its function in drought tolerance in Populus trichocarpa. Under treatment with exogenous abscisic acid and 6% PEG6000, DREB46 was rapidly and abundantly expressed. We successfully inserted P. trichocarpa DREB46 constructs into P. trichocarpa. After 11 d of drought stress and 3 d of rehydration treatment, the DREB46 over-expression (OE) lines exhibited significantly increased survival rates relative to the wild type (WT). Histochemical staining showed that the accumulation of reactive oxygen species (ROS) in transgenic plants under drought stress was lower than that in WT plants. Furthermore, OE plants displayed higher superoxide dismutase, peroxidase, and catalase activities and proline content, but lower malondialdehyde content than the WT plants under drought stress. In contrast, DREB46-RNA interference (RNAi) lines exhibited the opposite phenotype. Under PEG-6000 stress, OE plants produced significantly more adventitious roots (ARs) than WT plants. In contrast, RNAi-mediated DREB46-inhibited poplar exhibited fewer ARs. Quantitative real-time PCR indicated that WOX11/12a (Potri.013G066900), a gene related to root growth and development regulation, was significantly increased in OE plants. Additionally, yeast two-hybrid (Y2H) assays showed that DREB46 could interact with protein kinase MPK1 (Potri.002G032100) and protein phosphatase PP2C47 (Potri.007G058700), respectively, and this result was also verified by luciferase complementation assay. Transient co-expression results of leaves showed that PP2C47 and DREB46 Agrobacterium-transformed leaves had strong drought tolerance. These results show that DREB46 plays a key role in drought tolerance by inducing the ROS scavenging system and increasing the number of ARs.

Comprehensive analyses of the SPL transcription factor family in Paulownia fortunei and their responses to biotic and abiotic stresses

To study the molecular characteristics, phylogenetic evolution, and gene functions of the SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) genes in Paulownia fortunei, a whole genome sequence analysis was carried out, and a total of 23 PfSPL genes were identified. Tandem duplication and fragment replication were the main patterns of gene expansion in the PfSPL family. Phylogenetic analysis showed that the 23 identified PfSPLs formed seven subgroups, and the structures of the proteins in the same subgroup were similar. Functional analysis indicated that PfSPL11 may regulate flowering, PfSPL5 was involved in gibberellin signaling, PfSPL1/4/23 regulated branching, and PfSPL9/16/18 were related to pathogen resistance. Yeast one hybrid technology confirmed that PfSPL4 and PfSP23 can bind to the promoter of PfTCPa. The transcriptome analysis indicated that PfSPL10 was sensitive to both drought and salt stress. Ten PfSPLs that responded to phytoplasma infection were identified. Molecular docking showed that PfSPL10 and PfSPL 4/5/9/10/11/13 formed active pockets in the conserved SBP domain that could bind methyl methane sulfonate (MMS) and rifampicin (Rif) through stable hydrogen bonds, respectively. This study provides a basis for further studies on the functions of the PfSPL transcription factor family, and for genetic improvement and breeding of trees resistant to PaWB disease.

Basic helix-loop-helix transcription factor PxbHLH02 enhances drought tolerance in Populus (Populus simonii × P. nigra)

The basic helix-loop-helix (bHLH) transcription factors (TFs) are involved in plant morphogenesis and various abiotic and biotic stress responses. However, further exploration is required of drought-responsive bHLH family members and their detailed regulatory mechanisms in Populus. Two bHLH TF genes, PxbHLH01/02, were identified in Populus simonii × P. nigra and cloned. The aim of this study was to examine the role of bHLH TFs in drought tolerance in P. simonii × P. nigra. The results showed that the amino acid sequences of the two genes were homologous to Arabidopsis thaliana UPBEAT1 (AtUPB1) and overexpression of PxbHLH01/02 restored normal root length in the AtUPB1 insertional mutant (upb1-1). The PxbHLH01/02 gene promoter activity analysis suggested that they were involved in stress responses and hormone signaling. Furthermore, Arabidopsis transgenic lines overexpressing PxbHLH01/02 exhibited higher stress tolerance compared with the wild-type. Populus simonii × P. nigra overexpressing PxbHLH02 increased drought tolerance and exhibited higher superoxide dismutase and peroxidase activities, lower H2O2 and malondialdehyde content, and lower relative conductivity. The results of transcriptome sequencing (RNA-seq) and quantitative real-time PCR suggested that the response of PxbHLH02 to drought stress was related to abscisic acid (ABA) signal transduction. Overall, the findings of this study suggest that PxbHLH02 from P. simonii × P. nigra functions as a positive regulator of drought stress responses by regulating stomatal aperture and promoting ABA signal transduction.

Identification, classification, and expression profile analysis of heat shock transcription factor gene family in Salvia miltiorrhiza

In response to abiotic stresses, transcription factors are essential. Heat shock transcription factors (HSFs), which control gene expression, serve as essential regulators of plant growth, development, and stress response. As a model medicinal plant, Salvia miltiorrhiza is a crucial component in the treatment of cardiovascular illnesses. But throughout its growth cycle, S.miltiorrhiza is exposed to a series of abiotic challenges, including heat and drought. In this study, 35 HSF genes were identified based on genome sequencing of Salvia miltiorrhiza utilizing bioinformatics techniques. Additionally, 35 genes were classified into three groups by phylogeny and gene structural analysis, comprising 22 HSFA, 11 HSFB, and two HSFC. The distribution and sequence analysis of motif showed that SmHSFs were relatively conservative. In SmHSF genes, analysis of the promoter region revealed the presence of many cis-acting elements linked to stress, hormones, and growth and development, suggesting that these factors have regulatory roles. The majority of SmHSFs were expressed in response to heat and drought stress, according to combined transcriptome and real-time quantitative PCR (qRT-PCR) analyses. In conclusion, this study looked at the SmHSF gene family using genome-wide identification, evolutionary analysis, sequence characterization, and expression analysis. This research serves as a foundation for further investigations into the role of HSF genes and their molecular mechanisms in plant stress responses.

Global and gene-specific translational regulation in Escherichia coli across different conditions

How well mRNA transcript levels represent protein abundances has been a controversial issue. Particularly across different environments, correlations between mRNA and protein exhibit remarkable variability from gene to gene. Translational regulation is likely to be one of the key factors contributing to mismatches between mRNA level and protein abundance in bacteria. Here, we quantified genome-wide transcriptome and relative translation efficiency (RTE) under 12 different conditions in Escherichia coli. By quantifying the mRNA-RTE correlation both across genes and across conditions, we uncovered a diversity of gene-specific translational regulations, cooperating with transcriptional regulations, in response to carbon (C), nitrogen (N), and phosphate (P) limitations. Intriguingly, we found that many genes regulating translation are themselves subject to translational regulation, suggesting possible feedbacks. Furthermore, a random forest model suggests that codon usage partially predicts a gene's cross-condition variability in translation efficiency; such cross-condition variability tends to be an inherent quality of a gene, independent of the specific nutrient limitations. These findings broaden the understanding of translational regulation under different environments and provide novel strategies for the control of translation in synthetic biology. In addition, our data offers a resource for future multi-omics studies.

Integrated Omic Approaches Reveal Molecular Mechanisms of Tolerance during Soybean and Meloidogyne incognita Interactions

The root-knot nematode (RKN), Meloidogyne incognita, is a devastating soybean pathogen worldwide. The use of resistant cultivars is the most effective method to prevent economic losses caused by RKNs. To elucidate the mechanisms involved in resistance to RKN, we determined the proteome and transcriptome profiles from roots of susceptible (BRS133) and highly tolerant (PI 595099) Glycine max genotypes 4, 12, and 30 days after RKN infestation. After in silico analysis, we described major defense molecules and mechanisms considered constitutive responses to nematode infestation, such as mTOR, PI3K-Akt, relaxin, and thermogenesis. The integrated data allowed us to identify protein families and metabolic pathways exclusively regulated in tolerant soybean genotypes. Among them, we highlighted the phenylpropanoid pathway as an early, robust, and systemic defense process capable of controlling M. incognita reproduction. Associated with this metabolic pathway, 29 differentially expressed genes encoding 11 different enzymes were identified, mainly from the flavonoid and derivative pathways. Based on differential expression in transcriptomic and proteomic data, as well as in the expression profile by RT-qPCR, and previous studies, we selected and overexpressed the GmPR10 gene in transgenic tobacco to assess its protective effect against M. incognita. Transgenic plants of the T₂ generation showed up to 58% reduction in the M. incognita reproduction factor. Finally, data suggest that GmPR10 overexpression can be effective against the plant parasitic nematode M. incognita, but its mechanism of action remains unclear. These findings will help develop new engineered soybean genotypes with higher performance in response to RKN infections.

Overexpression of PagERF072 from Poplar Improves Salt Tolerance

Extreme environments, especially drought and high salt conditions, seriously affect plant growth and development. Ethylene-responsive factor (ERF) transcription factors play an important role in salt stress response. In this study, a significantly upregulated ERF gene was identified in 84K (Populus alba × P. glandulosa), which was named PagERF072. PagERF072 was confirmed to be a nuclear-localized protein. The results of yeast two-hybrid (Y2H) assay showed that PagERF072 protein exhibited no self-activating activity, and yeast one-hybrid (Y1H) demonstrated that PagERF072 could specifically bind to GCC-box element. Under salt stress, the transgenic poplar lines overexpressing PagERF072 showed improved salt tolerance. The activities of peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) in transgenic poplars were significantly increased relative to those of wild-type (WT) plants, whereas malondialdehyde (MDA) content showed an opposite trend. In addition, reactive oxygen species (ROS) was significantly reduced, and the expression levels of POD- and SOD-related genes were significantly increased in transgenic poplars under salt stress compared with WT. All results indicate that overexpression of the PagERF072 gene can improve the salt tolerance of transgenic poplars.

Identification of Functional Genetic Variations Underlying Flooding Tolerance in Brazilian Soybean Genotypes

Flooding is a frequent environmental stress that reduces soybean (Glycine max) growth and grain yield in many producing areas in the world, such as, e.g., in the United States, Southeast Asia and Southern Brazil. In these regions, soybean is frequently cultivated in lowland areas by rotating with rice (Oryza sativa), which provides numerous technical, economic and environmental benefits. Given these realities, this work aimed to characterize physiological responses, identify genes differentially expressed under flooding stress in Brazilian soybean genotypes with contrasting flooding tolerance, and select SNPs with potential use for marker-assisted selection. Soybean cultivars TECIRGA 6070 (flooding tolerant) and FUNDACEP 62 (flooding sensitive) were grown up to the V6 growth stage and then flooding stress was imposed. Total RNA was extracted from leaves 24 h after the stress was imposed and sequenced. In total, 421 induced and 291 repressed genes were identified in both genotypes. TECIRGA 6070 presented 284 and 460 genes up- and down-regulated, respectively, under flooding conditions. Of those, 100 and 148 genes were exclusively up- and down-regulated, respectively, in the tolerant genotype. Based on the RNA sequencing data, SNPs in differentially expressed genes in response to flooding stress were identified. Finally, 38 SNPs, located in genes with functional annotation for response to abiotic stresses, were found in TECIRGA 6070 and absent in FUNDACEP 62. To validate them, 22 SNPs were selected for designing KASP assays that were used to genotype a panel of 11 contrasting genotypes with known phenotypes. In addition, the phenotypic and grain yield impacts were analyzed in four field experiments using a panel of 166 Brazilian soybean genotypes. Five SNPs possibly related to flooding tolerance in Brazilian soybean genotypes were identified. The information generated from this research will be useful to develop soybean genotypes adapted to poorly drained soils or areas subject to flooding.

Lilium pumilum stress-responsive NAC transcription factor LpNAC17 enhances salt stress tolerance in tobacco

Lilium pumilum is a perennial herb with ornamental edible and medicinal value. It is an excellent wild germplasm resource with wide distribution and strong resistance. The NAC family of transcription factors is unique to higher plants. The NAC family plays a regulatory role in plant growth and development and participates in plant responses to biotic and abiotic stresses. The LpNAC17 gene of L. pumilum was cloned and transformed into tobacco to investigate the response of transgenic tobacco to salt stress. The results showed that the net photosynthetic rate and contents of chlorophyll in LpNAC17 over-expressed tobacco were higher than those in the control plants, while the stomatal conductance, transpiration rate and intercellular CO₂ concentration were lower than those in the controls. The activity of superoxide dismutase, peroxidase, catalase, and the content of proline in LpNAC17 over-expressed tobacco were higher than those in the controls, while the content of malondialdehyde, superoxide anion, and hydrogen peroxide were lower than that in the control. Nitro-blue tetrazolium staining and 3,3'-diaminobenzidine tissue localization showed that the contents of O 2 - and H₂O₂ in transgenic tobacco was lower than in the controls. The expression levels of NtSOD, NtPOD, NtCAT, NtHAK1, NtPMA4, and NtSOS1 in the transgenic tobacco were higher than those in the controls. Therefore, this study provides a gene source for molecular breeding of salt-tolerant plants through genetic engineering, and lays a foundation for further research on salt-tolerant Lily.

Apple U-box-type E3 ubiquitin ligase MdPUB23 reduces cold-stress tolerance by degrading the cold-stress regulatory protein MdICE1

Cold stress limits plant growth, geographical distribution, and crop yield. The MYC-type bHLH transcription factor ICE1 is recognized as the core positive regulator of the cold-stress response. However, how ICE1 protein levels are regulated remains to be further studied. In this study, we observed that a U-box-type E3 ubiquitin ligase, MdPUB23, positively regulated the cold-stress response in apple. The expression of MdPUB23 increased at both the transcriptional and post-translational levels in response to cold stress. Overexpression of MdPUB23 in transgenic apple enhanced sensitivity to cold stress. Further study showed that MdPUB23 directly interacted with MdICE1, promoting the ubiquitination-mediated degradation of the MdICE1 protein through the 26S-proteasome pathway and reducing the MdICE1-improved cold-stress tolerance in apple. Our results reveal that MdPUB23 regulates the cold-stress response by directly mediating the stability of the positive regulator MdICE1. The PUB23-ICE1 ubiquitination module may play a role in maintaining ICE1 protein homeostasis and preventing overreactions from causing damage to plants. The discovery of the ubiquitination regulatory pathway of ICE1 provides insights for the further exploration of plant cold-stress-response mechanisms.

A C2H2-type zinc finger transcription factor, MdZAT17, acts as a positive regulator in response to salt stress

Salt stress restricts plant growth and productivity worldwide. Zinc finger proteins play important roles in response to various abiotic plant stresses. In this research, we identified and characterized the ZAT17 gene in Malus domestica, which encodes a C2H2-type zinc finger protein. MdZAT17 has two typical conserved zinc finger domains and an ERF-associated amphiphilic repression (EAR) motif. Promoter analysis showed that MdZAT17 contains several stress-related response elements (ABRE, CGTCA-motif, and TC-rich repeats), and qRT-PCR analysis showed that the expression level of MdZAT17 was induced by various abiotic stress treatments. The overexpression of MdZAT17 improved tolerance to salt stress in apple calli. The ectopic expression of MdZAT17 in Arabidopsis enhanced salt stress tolerance and led to lower malondialdehyde (MDA) content, lower reactive oxygen species (ROS) accumulation, and greater anthocyanin accumulation under salt stress. Moreover, the overexpression of MdZAT17 transgenic apple calli and Arabidopsis reduced the sensitivity to abscisic acid (ABA). In conclusion, our results indicate that MdZAT17 plays a positive regulatory role in salt tolerance, providing a theoretical basis for further research on its molecular mechanisms.

Comparative transcriptome analysis of resistant and susceptible wheat in response to Rhizoctonia cerealis

BACKGROUND

Sheath blight is an important disease caused by Rhizoctonia cerealis that affects wheat yields worldwide. No wheat varieties have been identified with high resistance or immunity to sheath blight. Understanding the sheath blight resistance mechanism is essential for controlling this disease. In this study, we investigated the response of wheat to Rhizoctonia cerealis infection by analyzing the cytological changes and transcriptomes of common wheat 7182 with moderate sensitivity to sheath blight and H83 with moderate resistance.

RESULTS

The cytological observation showed that the growth of Rhizoctonia cerealis on the surface and its expansion inside the leaf sheath tissue were more rapid in the susceptible material. According to the transcriptome sequencing results, a total of 88685 genes were identified in both materials, including 20156 differentially expressed genes (DEGs) of which 12087 was upregulated genes and 8069 was downregulated genes. At 36 h post-inoculation, compared with the uninfected control, 11498 DEGs were identified in resistant materials, with 5064 downregulated genes and 6434 upregulated genes, and 13058 genes were detected in susceptible materials, with 6759 downregulated genes and 6299 upregulated genes. At 72 h post-inoculation, compared with the uninfected control, 6578 DEGs were detected in resistant materials, with 2991 downregulated genes and 3587 upregulated genes, and 7324 genes were detected in susceptible materials, with 4119 downregulated genes and 3205 upregulated genes. Functional annotation and enrichment analysis showed that the main pathways enriched for the DEGs included biosynthesis of secondary metabolites, carbon metabolism, plant hormone signal transduction, and plant-pathogen interaction. In particular, phenylpropane biosynthesis pathway is specifically activated in resistant variety H83 after infection. Many DEGs also belonged to the MYB, AP2, NAC, and WRKY transcription factor families.

CONCLUSIONS

Thus, we suggest that the normal functioning of plant signaling pathways and differences in the expression of key genes and transcription factors in some important metabolic pathways may be important for defending wheat against sheath blight. These findings may facilitate further exploration of the sheath blight resistance mechanism in wheat and the cloning of related genes.

CRISPR/Cas9 Mediated Knockout of the OsbHLH024 Transcription Factor Improves Salt Stress Resistance in Rice (Oryza sativa L.)

Salinity stress is one of the most prominent abiotic stresses that negatively affect crop production. Transcription factors (TFs) are involved in the absorption, transport, or compartmentation of sodium (Na⁺) or potassium (K⁺) to resist salt stress. The basic helix-loop-helix (bHLH) is a TF gene family critical for plant growth and stress responses, including salinity. Herein, we used the CRISPR/Cas9 strategy to generate the gene editing mutant to investigate the role of OsbHLH024 in rice under salt stress. The A nucleotide base deletion was identified in the osbhlh024 mutant (A91). Exposure of the A91 under salt stress resulted in a significant increase in the shoot weight, the total chlorophyll content, and the chlorophyll fluorescence. Moreover, high antioxidant activities coincided with less reactive oxygen species (ROS) and stabilized levels of MDA in the A91. This better control of oxidative stress was accompanied by fewer Na⁺ but more K⁺, and a balanced level of Ca²⁺, Zn²⁺, and Mg²⁺ in the shoot and root of the A91, allowing it to withstand salt stress. Furthermore, the A91 also presented a significantly up-regulated expression of the ion transporter genes (OsHKT1;3, OsHAK7, and OsSOS1) in the shoot when exposed to salt stress. These findings imply that the OsbHLH024 might play the role of a negative regulator of salt stress, which will help to understand better the molecular basis of rice production improvement under salt stress.

Genome-wide identification of Tomato Golden 2-Like transcription factors and abiotic stress related members screening

BACKGROUND

Golden 2-Like (G2-like) transcription factors play an important role in plant development. However, the roles of these G2-like regulatory genes in response to abiotic stresses in tomato are not well understood.

RESULTS

In this study, we identified 66 putative G2-like genes in tomato (Solanum lycopersicum) and classified them into 5 groups (I to V) according to gene structure, motif composition and phylogenetic analysis. The G2-like genes were unevenly distributed across all 12 chromosomes. There were nine pairs of duplicated gene segments and four tandem duplicated SlGlk genes. Analysis of the cis-regulatory elements (CREs) showed that the promoter regions of SlGlks contain many kinds of stress- and hormone-related CREs. Based on RNA-seq, SlGlks were expressed in response to three abiotic stresses. Thirty-six differentially expressed SlGlks were identified; these genes have multiple functions according to Gene Ontology (GO) analysis and are enriched mainly in the zeatin biosynthesis pathway. Further studies exhibited that silencing SlGlk16 in tomato would reduce drought stress tolerance by earlier wilted, lower superoxide dismutase (SOD), peroxidase (POD) activities, less Pro contents and more MDA contents.

CONCLUSIONS

Overall, the results of this study provide comprehensive information on G2-like transcription factors and G2-like genes that may be expressed in response to abiotic stresses.

Physiological and transcriptomic analysis of Cabernet Sauvginon (Vitis vinifera L.) reveals the alleviating effect of exogenous strigolactones on the response of grapevine to drought stress

Drought stress can significantly affect the growth and yield of grapevine. The application of exogenous strigolactone can relieve the drought symptoms of grapevine; however, little is known about the transcription levels in grapevine under drought stress following exogenous strigolactone application. The mitigative effect of exogenous strigolactone on grapevine leaves under drought stress was studied by transcriptome analysis based on RNA sequencing. On the 10th day of drought stress, the strigolactone treatment group had a higher relative water content and lower electrical conductivity, which significantly alleviated the drought damage. Compared to the drought (D) group, a total of 5955 differentially expressed genes (DEGs) (2966 up-regulated genes and 2989 down-regulated genes) were detected in the exogenous strigolactone (DG) groups. Based on Gene Ontology analysis, the DEGs in the D and DG treatments were enriched in the processes of photosynthesis and organic acid catabolism. Pathway analysis showed that the DEGs in the D and DG treatments were enriched in carbon metabolism, ribosome, starch and sucrose metabolism, flavonoid biosynthesis, and circadian rhythm. Additionally, in the DG group, the antioxidant enzyme genes of CAT1, GSHPX1, GSHPX2, POD42, APX6, and SODCP were up-regulated, two NAC, three WRKY, and four MYB transcription factor genes were down-regulated, and the key gene of strigolactone synthesis D14 was up-regulated, compared with that in the D group. The results provide a new perspective for studying the adaptation of plants to drought stress.

Transcription Factor GmWRKY46 Enhanced Phosphate Starvation Tolerance and Root Development in Transgenic Plants

Phosphorus (P) is one of the essential macronutrients, whose deficiency limits the growth and development of plants. In this study, we investigated the possible role of GmWRKY46 in the phosphate (Pi) starvation stress tolerance of soybean. GmWRKY46 belonged to the group III subfamily of the WRKY transcription factor family, which was localized in the nucleus and had transcriptional activator activity. GmWRKY46 could be strongly induced by Pi starvation, especially in soybean roots. Overexpression of GmWRKY46 significantly enhanced tolerance to Pi starvation and lateral root development in transgenic Arabidopsis. RNA-seq analysis showed that overexpression of GmWRKY46 led to change in many genes related to energy metabolisms, stress responses, and plant hormone signal transduction in transgenic Arabidopsis. Among these differential expression genes, we found that overexpression of AtAED1 alone could enhance the tolerance of transgenic Arabidopsis to Pi starvation. Y1H and ChIP-qPCR analyses showed that GmWRKY46 could directly bind to the W-box motif of the AtAED1 promoter in vitro and in vivo. Furthermore, results from intact soybean composite plants with GmWRKY46 overexpression showed that GmWRKY46 was involved in hairy roots development and subsequently affected plant growth and Pi uptake. These results provide a basis for the molecular genetic breeding of soybean tolerant to Pi starvation.

Transcriptome characterization and expression profile of Coix lacryma-jobi L. in response to drought

Coix lacryma-jobi L. is a very important economic crop widely cultivated in Southeast Asia. Drought affects more than four million square kilometers every year, and is a significant factor limiting agricultural productivity. However, relatively little is known about how Coix lacryma-jobi L. responds to drought treatments. To obtain a detailed and comprehensive understanding of the mechanisms regulating the transcriptional responses of Coix lacryma-jobi L. to drought treatment, we employed high throughput short-read sequencing of cDNA prepared from polyadenylated RNA to explore global gene expression after a seven-day drought treatment. We generated a de novo assembled transcriptome comprising 65,480 unique sequences. Differential expression analysis based on RSEM-estimated transcript abundances identified 5,315 differentially expressed genes (DEGs) when comparing samples from plants following drought-treatment and from the appropriate controls. Among these, the transcripts for 3,460 genes were increased in abundance, whereas 1,855 were decreased. Real-time quantitative PCR for 5 transcripts confirmed the changes identified by RNA-Seq. The results provide a transcriptional overview of the changes in Coix lacryma-jobi L. in response to drought, and will be very useful for studying the function of associated genes and selection of molecular marker of Coix lacryma-jobi L in the future.

The barley SHN1-type transcription factor HvSHN1 imparts heat, drought and salt tolerances in transgenic tobacco

The APETAL2/Ethylene Responsive Factor (AP2/ERF) family was the subject of intensive research which led to the identification of several members involved in different stress responses such as salinity, drought and high temperature. The SHN/WIN clade of AP2/ERF participates in many important processes such as cutin and wax biosynthesis, ethylene signaling and gene expression. Here, we report the functional analysis of SHN1-type transcription factor, HvSHN1, from barely. The overexpression of HvSHN1 under the control of the duplicated 35S promoter in transgenic tobacco plants improved tolerance to salt, water stress and heat stress. Transgenic lines exhibited altered permeability of the cuticle and decreased stomatal density. Under heat stress, HvSHN1 transgenic lines exhibited higher superoxide dismutase (SOD) and catalase (CAT) activity and lower MDA and H2O2 contents than did WT. The overexpression of HvSHN1 upregulated different genes involved in osmotic stress, oxidative stress, sugar metabolism, and wax biosynthesis. To understand the involvement of HvSHN1 in heat stress tolerance, promoter regions of two tobacco genes homologous to Arabidopsis genes HSP90.1 and RAP2.6 were analyzed and DRE cis-elements; binding sites of HvSHN1, were found. Interaction network of HvSHN1, predicted using STRING software, contained proteins with predicted functions related to lipids metabolism and a gene encoding Cyclin-Dependent Kinase. These results suggest that HvSHN1 is an interesting candidate for the improvement of abiotic stress tolerance especially in the context of climate change.

Transcriptome Analysis of Tolerant and Susceptible Maize Genotypes Reveals Novel Insights about the Molecular Mechanisms Underlying Drought Responses in Leaves

Maize (Zea mays L.) is the most essential food crop in the world. However, maize is highly susceptible to drought stress, especially at the seedling stage, and the molecular mechanisms underlying drought tolerance remain elusive. In this study, we conducted comparative transcriptome and physiological analyses of drought-tolerant (CML69) and susceptible (LX9801) inbred lines subjected to drought treatment at the seedling stage for three and five days. The tolerant line had significantly higher relative water content in the leaves, as well as lower electrolyte leakage and malondialdehyde levels, than the susceptible line. Using an RNA-seq-based approach, we identified 10,084 differentially expressed genes (DEGs) with 6906 and 3178 DEGs been annotated and unannotated, respectively. Two critical sets of drought-responsive DEGs, including 4687 genotype-specific and 2219 common drought-responsive genes, were mined out of the annotated DEGs. The tolerant-line DEGs were predominantly associated with the cytoskeleton, cell wall modification, glycolysis/gluconeogenesis, transport, osmotic regulation, drought avoidance, ROS scavengers, defense, and transcriptional factors. For the susceptible line, the DEGs were highly enriched in the photosynthesis, histone, and carbon fixation pathways. The unannotated DEGs were implicated in lncRNAs, including 428 previously reported and 22% putative TE-lncRNAs. There was consensus on both the physiological response and RNA-seq outcomes. Collectively, our findings will provide a comprehensive basis of the molecular networks mediating drought stress tolerance of maize at the seedling stage.

Genome-wide identification of AP2/EREBP in Fragaria vesca and expression pattern analysis of the FvDREB subfamily under drought stress

BACKGROUND

Drought is a common phenomenon worldwide. It is also one of the main abiotic factors that affect the growth and quality of strawberry. The dehydration-responsive element binding protein (DREB) members that belong to the APETALA2/ethylene-responsive element binding protein (AP2/EREBP) superfamily are unique transcription factors in plants that play important roles in the abiotic stress response.

RESULTS

Here, a total of 119 AP2/EREBP genes were identified in Fragaria vesca, and the AP2/EREBP superfamily was divided into AP2, RAV, ERF, DREB, and soloist subfamilies, containing 18, 7, 61, 32, and one member(s), respectively. The DREB subfamily was further divided into six subgroups (A-1 to A-6) based on phylogenetic analysis. Gene structure, conserved motifs, chromosomal location, and synteny analysis were conducted to comprehensively investigate the characteristics of FvDREBs. Furthermore, transcriptome analysis revealed distinctive expression patterns among the FvDREB genes in strawberry plants exposed to drought stress. The expression of FvDREB6 of the A-2 subgroup was down-regulated in old leaves and up-regulated in young leaves in response to drought. Furthermore, qRT-PCR analysis found that FvDREB8 from the A-2 subgroup had the highest expression level under drought stress. Together, analyses with the expression pattern, phylogenetic relationship, motif, and promoter suggest that FvDREB18 may play a critical role in the regulation of FvDREB1 and FvDREB2 expression.

CONCLUSIONS

Our findings provide new insights into the characteristics and potential functions of FvDREBs. These FvDREB genes should be further studied as they appear to be excellent candidates for drought tolerance improvement of strawberry.

Using Network-Based Machine Learning to Predict Transcription Factors Involved in Drought Resistance

Gene regulatory networks underpin stress response pathways in plants. However, parsing these networks to prioritize key genes underlying a particular trait is challenging. Here, we have built the Gene Regulation and Association Network (GRAiN) of rice (Oryza sativa). GRAiN is an interactive query-based web-platform that allows users to study functional relationships between transcription factors (TFs) and genetic modules underlying abiotic-stress responses. We built GRAiN by applying a combination of different network inference algorithms to publicly available gene expression data. We propose a supervised machine learning framework that complements GRAiN in prioritizing genes that regulate stress signal transduction and modulate gene expression under drought conditions. Our framework converts intricate network connectivity patterns of 2160 TFs into a single drought score. We observed that TFs with the highest drought scores define the functional, structural, and evolutionary characteristics of drought resistance in rice. Our approach accurately predicted the function of OsbHLH148 TF, which we validated using in vitro protein-DNA binding assays and mRNA sequencing loss-of-function mutants grown under control and drought stress conditions. Our network and the complementary machine learning strategy lends itself to predicting key regulatory genes underlying other agricultural traits and will assist in the genetic engineering of desirable rice varieties.

Wheat Varietal Response to Tilletia controversa J. G. Kühn Using qRT-PCR and Laser Confocal Microscopy

Tilletia controversa J. G. Kühn is a causal organism of dwarf bunt in wheat. Understanding the interaction of wheat and T. controversa is of practical and scientific importance for disease control. In this study, the relative expression of TaLHY and TaPR-4 and TaPR-5 genes was higher in a resistant (Yinong 18) and moderately resistant (Pin 9928) cultivars rather than susceptible (Dongxuan 3) cultivar at 72 h post inoculation (hpi) with T. controversa. Similarly, the expression of defensin, TaPR-2 and TaPR-10 genes was observed higher in resistant and moderately resistant cultivars after exogenous application of phytohormones, including methyl jasmonate, salicylic acid, and abscisic acid. Laser confocal microscopy was used to track the fungal hyphae in the roots, leaves, and tapetum cells, which of susceptible cultivar were infected harshly by T. controversa than moderately resistant and resistant cultivars. There were no fungal hyphae in tapetum cells in susceptible cultivar after methyl jasmonate, salicylic acid and abscisic acid treatments. Moreover, after T. controversa infection, the pollen germination was of 80.06, 58.73, and 0.67% in resistant, moderately resistant and susceptible cultivars, respectively. The above results suggested that the use using of resistant cultivar is a good option against the dwarf bunt disease.

Enhanced tolerance to drought stress resulting from Caragana korshinskii CkWRKY33 in transgenic Arabidopsis thaliana

Background

It is well known that WRKY transcription factors play important roles in plant growth and development, defense regulation and stress responses.

Results

In this study, a WRKY transcription factor, WRKY33, was cloned from Caragana korshinskii. A sequence structure analysis showed that it belonged to the Group-I type. Subcellular localization experiments in tobacco epidermal cells showed the presence of CkWRKY33 in the nucleus. Additionally, CkWRKY33 was overexpressed in Arabidopsis thaliana. A phenotypic investigation revealed that compared with wild-type plants, CkWRKY33-overexpressing transgenic plants had higher survival rates, as well as relative soluble sugar, proline and peroxidase contents, but lower malondialdehyde contents, following a drought stress treatment.

Conclusions

This suggested that the overexpression of CkWRKY33 led to an enhanced drought-stress tolerance in transgenic A. thaliana. Thus, CkWRKY33 may act as a positive regulator involved in the drought-stress responses in Caragana korshinskii.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12863-021-00965-4.

Stress-responsive tomato gene SlGRAS4 function in drought stress and abscisic acid signaling

Adverse environmental conditions such as drought stress greatly limit the growth and production of crops worldwide. In this study, SlGRAS4, a drought stress-responsive GRAS gene from tomato (Solanum lycopersicum) was functionally characterized. Repressing SlGRAS4 (SlGRAS4-RNAi) increased sensitivity to drought stress, whereas overexpressing SlGRAS4 (SlGRAS4-OE) in tomato enhanced tolerance of this stress. Under stress condition SlGRAS4-OE plants accumulated much less ROS than wild-type and SlGRAS4-RNAi plants. Numerous dehydration induced ROS-scavenging genes were upregulated in SlGRAS4-OE plants after drought stress, implying that SlGRAS4 confers drought tolerance by modulating ROS homeostasis. On the other hand, there are several abscisic acid (ABA)-responsive elements in SlGRAS4 promoter, the relative expression of ABA signaling genes including SlPYLs, SlPP2Cs and SlSnRK2s were verified in WT and transgenic plants both under normal and drought stress, the changed drought sensitivity of transgenic plants was mainly caused by SlSnRK2s, the positive regulators of ABA signaling. Our results suggested that SlGRAS4 directly binds to and activates SlSnRK2.4 promoter, belongs to subclass III SnRK2s, which play crucial role in ABA signaling. Protein studies revealed that SlSnRK2.4 interacts with SlAREB1 and SlAREB2, the major downstream transcription factors of ABA-dependent signaling pathway. SlGRAS4 therefore confers drought tolerance may be through SnRK2-AREB pathway.

TaAP2-15, An AP2/ERF Transcription Factor, Is Positively Involved in Wheat Resistance to Puccinia striiformis f. sp. tritici

AP2 transcription factors play a crucial role in plant development and reproductive growth, as well as response to biotic and abiotic stress. However, the role of TaAP2-15, in the interaction between wheat and the stripe fungus, Puccinia striiformis f. sp. tritici (Pst), remains elusive. In this study, we isolated TaAP2-15 and characterized its function during the interaction. TaAP2-15 was localized in the nucleus of wheat and N. benthamiana. Silencing of TaAP2-15 by barley stripe mosaic virus (BSMV)-mediated VIGS (virus-induced gene silencing) increased the susceptibility of wheat to Pst accompanied by enhanced growth of the pathogen (number of haustoria, haustorial mother cells and hyphal length). We confirmed by quantitative real-time PCR that the transcript levels of pathogenesis-related genes (TaPR1 and TaPR2) were down-regulated, while reactive oxygen species (ROS)-scavenging genes (TaCAT3 and TaFSOD3D) were induced accompanied by reduced accumulation of H₂O₂. Furthermore, we found that TaAP2-15 interacted with a zinc finger protein (TaRZFP34) that is a homolog of OsRZFP34 in rice. Together our findings demonstrate that TaAP2-15 is positively involved in resistance of wheat to the stripe rust fungus and provides new insights into the roles of AP2 in the host-pathogen interaction.

Genome-wide analysis of AP2/ERF transcription factors in pineapple reveals functional divergence during flowering induction mediated by ethylene and floral organ development

The APETALA2/ethylene-responsive factor (AP2/ERF) has important roles in regulating developmental processes and hormone signaling transduction in plants. Pineapple demonstrates a special sensitivity to ethylene, and AP2/ERFs may contribute to this distinct sensitivity of pineapples to ethylene. However, little information is available on the AP2/ERF of pineapple. In this study, 97 AP2/ERF family members were identified from the pineapple genome. The AcAP2/ERF superfamily could be further divided into five subfamilies, and different subfamily existed functional divergence in multifarious biological processes. ERF and RAV subfamily genes might play important roles in the process of ethylene response of pineapple; ERF and DREB subfamily genes had particular functions in the floral organ development. This study is the first to provide detailed information on the features of AP2/ERFs in pineapple, provide new insights into the potential functional roles of the AP2/ERF superfamily members, and will facilitate a better understanding of the molecular mechanism of flower in pineapple.

Using Network-Based Machine Learning to Predict Transcription Factors Involved in Drought Resistance

Gene regulatory networks underpin stress response pathways in plants. However, parsing these networks to prioritize key genes underlying a particular trait is challenging. Here, we have built the Gene Regulation and Association Network (GRAiN) of rice (Oryza sativa). GRAiN is an interactive query-based web-platform that allows users to study functional relationships between transcription factors (TFs) and genetic modules underlying abiotic-stress responses. We built GRAiN by applying a combination of different network inference algorithms to publicly available gene expression data. We propose a supervised machine learning framework that complements GRAiN in prioritizing genes that regulate stress signal transduction and modulate gene expression under drought conditions. Our framework converts intricate network connectivity patterns of 2160 TFs into a single drought score. We observed that TFs with the highest drought scores define the functional, structural, and evolutionary characteristics of drought resistance in rice. Our approach accurately predicted the function of OsbHLH148 TF, which we validated using in vitro protein-DNA binding assays and mRNA sequencing loss-of-function mutants grown under control and drought stress conditions. Our network and the complementary machine learning strategy lends itself to predicting key regulatory genes underlying other agricultural traits and will assist in the genetic engineering of desirable rice varieties.

Genome-wide study of pineapple (Ananas comosus L.) bHLH transcription factors indicates that cryptochrome-interacting bHLH2 (AcCIB2) participates in flowering time regulation and abiotic stress response

BACKGROUND

Transcription factors (TFs) are essential regulators of growth and development in eukaryotes. Basic-helix-loop-helix (bHLHs) is one of the most significant TFs families involved in several critical regulatory functions. Cryptochrome-interacting bHLH (CIB) and cryptochromes form an extensive regulatory network to mediate a plethora of pathways. Although bHLHs regulate critical biological processes in plants, the information about pineapple bHLHs remains unexplored.

RESULTS

Here, we identified a total of 121 bHLH proteins in the pineapple genome. The identified genes were renamed based on the ascending order of their gene ID and classified into 18 subgroups by phylogenetic analysis. We found that bHLH genes are expressed in different organs and stages of pineapple development. Furthermore, by the ectopic expression of AcCIB2 in Arabidopsis and complementation of Atcib2 mutant, we verified the involvement of AcCIB2 in photomorphogenesis and abiotic stress response.

CONCLUSIONS

Our findings revealed that AcCIB2 plays an essential role in flowering time regulation and abiotic stress response. The present study provides additional insights into the current knowledge of bHLH genes and suggests their potential role in various biological processes during pineapple development.

Screening of Virulence-Related Transcriptional Regulators in Streptococcus suis

Streptococcus suis (S.suis) is an important zoonotic pathogen that causes many severe diseases in pigs and humans. Virulence-related transcriptional regulators have been widely reported in pathogenic microorganisms, but only a few have been identified in S.suis. Our aim was to screen virulence-related transcriptional regulators in S.suis. A total of 89 such genes were predicted in the S.suis genome, of which 22 were up-regulated and 18 were down-regulated during S.suis infection in mice. To evaluate the roles of these differentially expressed factors in S.suis virulence, deletion mutants were constructed, and 10 mutants were successfully obtained. Among these genes, the deletion of comR, sitR, or sxvR caused significantly decreased virulence in mice, compared to that with the wild-type strain. Moreover, the survival of ΔcomR, ΔsitR, and ΔsxvR mutant strains in blood was significantly reduced both in vitro and in vivo. Furthermore, their pro-inflammatory abilities were also obviously decreased in vivo. The regulatory mechanisms of comR, sitR, and sxvR were then analyzed by whole transcriptome RNA sequencing (RNA-Seq). Results indicated that the absence of comR induced the down-regulation of 17 virulence factors or virulence-related factors, including genes involved in the synthesis of capsules, oxidative stress tolerance, immune evasion, and cell division. Furthermore, three and two virulence factors or virulence-related factors were down-regulated upon deletion of sitR and sxvR, respectively. Thus, this study reports the discovery of three virulence-associated transcriptional regulatory factors in S.suis. These factors could ultimately be targeted to control infection caused by these bacteria.

Transcriptome Analysis of Cryphonectria parasitica Infected With Cryphonectria hypovirus 1 (CHV1) Reveals Distinct Genes Related to Fungal Metabolites, Virulence, Antiviral RNA-Silencing, and Their Regulation

Comprehensive transcriptome analysis was conducted to elucidate the molecular basis of the interaction between chestnut blight fungus, Cryphonectria parasitica, and single-stranded RNA (ssRNA) mycovirus Cryphonectria hypovirus 1 (CHV1), using RNA-sequencing (RNA-seq). A total of 1,023 differentially expressed genes (DEGs) were affected by CHV1 infection, of which 753 DEGs were upregulated and 270 DEGs were downregulated. Significant correlations in qRT-PCR analysis of 20 randomly selected DEGs and agreement with previously characterized marker genes validated our RNA-seq analysis as representing global transcriptional profiling of virus-free and -infected isogenic strains of C. parasitica. Gene Ontology (GO) analysis of DEGs indicated that “cellular aromatic compound metabolic process” and “transport” were the two most enriched components in the “biological process.” In addition, “cytoplasm” was the most enriched term in the “cellular component” and “nucleotide binding” and “cation binding” were the two most enriched terms in the “molecular function” category. These results suggested that altered expression of genes encoding numerous intracellular proteins due to hypoviral infection resulted in changes in specific metabolic processes as well as transport processes. Kyoto Encyclopedia of Genes and Genomes function analysis demonstrated that pathways for “biosynthesis of other secondary metabolites,” “amino acid metabolism,” “carbohydrate metabolism,” and “translation” were enriched among the DEGs in C. parasitica. These results demonstrate that hypoviral infection resulted in massive but specific changes in primary and secondary metabolism, of which antiviral fungal metabolites were highly induced. The results of this study provide further insights into the mechanism of fungal gene regulation by CHV1 at the transcriptome level.

Gene regulation underpinning increased thermal tolerance in a laboratory-evolved coral photosymbiont

Small increases in ocean temperature can disrupt the obligate symbiosis between corals and dinoflagellate microalgae, resulting in coral bleaching. Little is known about the genes that drive the physiological and bleaching response of algal symbionts to elevated temperature. Moreover, many studies to-date have compared highly divergent strains, making it challenging to accredit specific genes to contrasting traits. Here, we compare transcriptional responses at ambient (27°C) and bleaching-relevant (31°C) temperatures in a monoclonal, wild-type (WT) strain of Symbiodiniaceae to those of a selected-strain (SS), derived from the same monoclonal culture and experimentally evolved to elevated temperature over 80 generations (2.5 years). Thousands of genes were differentially expressed at a log fold-change of >8 between the WT and SS over a 35 days temperature treatment period. At 31°C, WT cells exhibited a temporally unstable transcriptomic response upregulating genes involved in the universal stress response such as molecular chaperoning, protein repair, protein degradation and DNA repair. Comparatively, SS cells exhibited a temporally stable transcriptomic response and downregulated many stress response genes that were upregulated by the WT. Among the most highly upregulated genes in the SS at 31°C were algal transcription factors and a gene probably of bacterial origin that encodes a type II secretion system protein, suggesting interactions with bacteria may contribute to the increased thermal tolerance of the SS. Genes and functional pathways conferring thermal tolerance in the SS could be targeted in future genetic engineering experiments designed to develop thermally resilient algal symbionts for use in coral restoration and conservation.

NAC Family Transcription Factors in Carrot: Genomic and Transcriptomic Analysis and Responses to Abiotic Stresses

Carrot is an annual or biennial herbaceous plant of the Apiaceae family. Carrot is an important vegetable, and its fresh taproot, which contains rich nutrients, is the main edible part. In the life cycle of carrot, NAC family transcription factors (TFs) are involved in almost all physiological processes. The function of NAC TFs in carrot remains unclear. In this study, 73 NAC family TF members in carrot were identified and characterized using transcriptome and genome databases. These members were divided into 14 subfamilies. Multiple sequence alignment was performed, and the conserved domains, common motifs, phylogenetic tree, and interaction network of DcNAC proteins were predicted and analyzed. Results showed that the same group of NAC proteins of carrot had high similarity. Eight DcNAC genes were selected to detect their expression profiles under abiotic stress treatments. The expression levels of the selected DcNAC genes significantly increased under treatments with low temperature, high temperature, drought, and salt stress. Results provide potentially useful information for further analysis of the roles of DcNAC transcription factors in carrot.

A Wheat WRKY Transcription Factor TaWRKY46 Enhances Tolerance to Osmotic Stress in transgenic Arabidopsis Plants

WRKY transcription factors play central roles in developmental processes and stress responses of wheat. Most WRKY proteins of the same group (Group III) have a similar function in abiotic stress responses in plants. TaWRKY46, a member of Group III, was up-regulated by PEG treatment. TaWRKY46-GFP fusion proteins localize to the nucleus in wheat mesophyll protoplasts. Overexpression of TaWRKY46 enhanced osmotic stress tolerance in transgenic Arabidopsis thaliana plants, which was mainly demonstrated by transgenic Arabidopsis plants forming higher germination rate and longer root length on 1/2 Murashige and Skoog (MS) medium containing mannitol. Furthermore, the expression of several stress-related genes (P5CS1, RD29B, DREB2A, ABF3, CBF2, and CBF3) was significantly increased in TaWRKY46-overexpressing transgenic Arabidopsis plants after mannitol treatment. Taken together, these findings proposed that TaWRKY46 possesses vital functions in improving drought tolerance through ABA-dependent and ABA-independent pathways when plants are exposed to adverse osmotic conditions. TaWRKY46 can be taken as a candidate gene for transgenic breeding against osmotic stress in wheat. It can further complement and improve the information of the WRKY family members of Group III.

Molecular bases for drought tolerance in common vetch: designing new molecular breeding tools

BACKGROUND

Common vetch (Vicia sativa L.) is a forage grain legume of high protein content and high nitrogen fixation, relevant in sustainable agriculture systems. Drought is the main limiting factor of this crop yield. Genetic resources collections are essential to provide genetic variability for breeding. The analysis of drought associated parameters has allowed us to identify drought tolerant and sensitive ecotypes in a vetch core collection.

RESULTS

To understand the mechanisms involved in drought response we analysed transcriptomic differences between tolerant and sensitive accessions. Polymorphic variants (SNPs and SSRs) in these differential expressed genes (DEGs) have also been analysed for the design of drought-associated markers. A total of 1332 transcripts were commonly deregulated in both genotypes under drought. To know the drought adaptive response, we also analysed DEGs between accessions. A total of 2646 transcripts are DEG between sensitive and tolerant ecotypes, in watered and drought conditions, including important genes involved in redox homeostasis, cell wall modifications and stress-response. The integration of this functional and genetic information will contribute to understand the molecular mechanisms of drought response and the adaptive mechanisms of drought tolerance in common vetch. The identification of polymorphic variants in these DEGs has also been screened for the design of drought-associated markers that could be used in future breeding program strategies.

CONCLUSIONS

Our studies shed light for the first time in common vetch about the genes and pathways associated with drought tolerance. In addition, we identify over 100 potential drought associated polymorphism, as SNPs or SSRs, which are differently present in drought and tolerant genotypes. The use of these molecular markers for trait prediction would enable the development of genomic tools for future engineering strategies by screening of germplasm crop collections for traits related with crop drought resilience, adaptability or yield in vetch.

Transcriptome-wide identification of novel circular RNAs in soybean in response to low-phosphorus stress

Low-phosphorus (LP) stress is a major factor limiting the growth and yield of soybean. Circular RNAs (circRNAs) are novel noncoding RNAs that play a crucial role in plant responses to abiotic stress. However, how LP stress mediates the biogenesis of circRNAs in soybean remains unclear. Here, to explore the response mechanisms of circRNAs to LP stress, the roots of two representative soybean genotypes with different P-use efficiency, Bogao (a LP-sensitive genotype) and Nannong 94156 (a LP-tolerant genotype), were used for the construction of RNA sequencing (RNA-seq) libraries and circRNA identification. In total, 371 novel circRNA candidates, including 120 significantly differentially expressed (DE) circRNAs, were identified across different P levels and genotypes. More DE circRNAs were significantly regulated by LP stress in Bogao than in NN94156, suggesting that the tolerant genotype was less affected by LP stress than the sensitive genotype was; in other words, NN94156 may have a better ability to maintain P homeostasis under LP stress. Moreover, a positive correlation was observed between the expression patterns of P stress-induced circRNAs and their circRNA-host genes. Gene Ontology (GO) enrichment analysis of these circRNA-host genes and microRNA (miRNA)-targeted genes indicated that these DE circRNAs were involved mainly in defense responses, ADP binding, nucleoside binding, organic substance catabolic processes, oxidoreductase activity, and signal transduction. Together, our results revealed that LP stress can significantly alter the genome-wide profiles of circRNAs and indicated that the regulation of circRNAs was both genotype and environment specific in response to LP stress. LP-induced circRNAs might provide a rich resource for LP-responsive circRNA candidates for future studies.

Epigenetic signatures of stress adaptation and flowering regulation in response to extended drought and recovery in Zea mays

During their lifespan, plants respond to a multitude of stressful factors. Dynamic changes in chromatin and concomitant transcriptional variations control stress response and adaptation, with epigenetic memory mechanisms integrating environmental conditions and appropriate developmental programs over the time. Here we analyzed transcriptome and genome-wide histone modifications of maize plants subjected to a mild and prolonged drought stress just before the flowering transition. Stress was followed by a complete recovery period to evaluate drought memory mechanisms. Three categories of stress-memory genes were identified: i) "transcriptional memory" genes, with stable transcriptional changes persisting after the recovery; ii) "epigenetic memory candidate" genes in which stress-induced chromatin changes persist longer than the stimulus, in absence of transcriptional changes; iii) "delayed memory" genes, not immediately affected by the stress, but perceiving and storing stress signal for a delayed response. This last memory mechanism is described for the first time in drought response. In addition, applied drought stress altered floral patterning, possibly by affecting expression and chromatin of flowering regulatory genes. Altogether, we provided a genome-wide map of the coordination between genes and chromatin marks utilized by plants to adapt to a stressful environment, describing how this serves as a backbone for setting stress memory.

Overexpression of Ks-type dehydrins gene OeSRC1 from Olea europaea increases salt and drought tolerance in tobacco plants

Agricultural production is greatly affected by environmental stresses, such as cold, drought and high-salinity. It is possible to produce tolerant genotypes by transferring genes encoding protective proteins or enzymes from other organisms. In this regard, the current study was aimed to clone a novel OeSRC1 gene identified during the transcriptome profiling of olives (Olea europaea L.) and to investigate the function of this gene in tobacco plants. Functional evaluation of OeSRC1 gene in putative transgenic tobacco plants were carried out under drought, cold and salt stress conditions by using molecular and biochemical tools. It was observed that the transgenic tobacco plants exhibited higher seed germination and survival rates, better root and shoot growth under cold, salt and drought stress treatments compared to wild type plants. Our results also demonstrated that, under stress conditions, transgenic plants accumulated more free proline while no significant changes were observed regarding electrolyte leakage. Ascorbate peroxidase activity of OeSRC1-overexpressing plants was higher than those of the WT plants under different stress conditions. The overall results demonstrate the explicit role of OeSRC1 gene in conferring multiple abiotic stress tolerance at the whole-plant level. The multifunctional role of olive OeSRC1 gene looks good to enhance environmental stress tolerance in diverse plants.

Microarray analysis of transcriptional responses to salt and drought stress in Arabidopsis thaliana

Microarray expression profile analysis is a useful approach to increase our knowledge about genes involved in regulatory networks and signal transduction pathways related to abiotic stress tolerance. Salt and drought, as two important abiotic stresses, adversely affect plant productivity in the world every year. To understand stress response mechanisms and identify genes and proteins which play critical roles in these mechanisms, the study of individual genes and proteins cannot be considered as an effective approach. On the other hand, the availability of new global data provides us an effective way to shed some light on the central role of molecules involved in stress response mechanisms in the plant. A meta-analysis of salt and drought stress responses was carried out using 38 samples of different experiments from leaves and roots of Arabidopsis plants exposed to drought and salt stresses. We figured out the number of differentially expressed genes (DEGs) was higher in roots under both stresses. Also, we found that the number of common DEGs under both stresses was more in roots and also the number of common DEGs in both tissues under salt stress was more than drought stress. The highest percent of DEGs was related to cell and cell part (about 87%). Around 9% and 7% of DEGs in roots and leaves encoded transcription factors, respectively. Network analysis revealed that three transcription factor families HSF, AP2/ERF and C2H2, may have critical roles in salt and drought stress response mechanisms in Arabidopsis ​and some proteins like STZ may be introduced as a new candidate gene for enhancing salt and drought tolerance in crop plants.

MdGRF11, an apple 14-3-3 protein, acts as a positive regulator of drought and salt tolerance

The 14-3-3 proteins are a family of highly conserved phosphoserine-binding proteins that participate in the regulation of diverse physiological and developmental processes. In this research, twenty 14-3-3 genes in apples, which contained a highly conserved 14-3-3 domain, were identified and divided into two subgroups. Among them, MdGRF11 was further cloned and investigated. qRT-PCR analyses and GUS staining show that MdGRF11 is expressed in various organs and tissues with the highest expression levels found in the fruit. MdGRF11 was upregulated by polyethylene glycol 6000 (PEG 6000), NaCl, abscisic acid (ABA) and low temperature (4 °C) treatments. MdGRF11-overexpressing transgenic Arabidopsis and apple calli exhibited reduced sensitivity to salt and PEG 6000 treatments. Moreover, the ectopic expression of MdGRF11 improved the tolerance of transgenic tobacco to salt and drought stresses, which grew longer roots, underwent more growth, and presented higher chlorophyll levels than the wild-type control under salt and drought stress conditions. Furthermore, MdGRF11 expression remarkably reduced electrolyte leakage, malondialdehyde content levels, H₂O₂ and O2- accumulation under salt and drought stress conditions, which relied on the regulation of ROS-scavenging signaling to reduce oxidative damage of cells after salt and drought stress treatment. MdGRF11 also enhanced tolerance to stress by upregulating expression levels of ROS-scavenging and stress-related genes, especially improving responses to drought stress by modifying the water loss rates and stomatal aperture. Moreover, MdGRF11 could interact with MdAREB/ABF transcription factors through yeast two hybrid analyses. In conclusion, our results indicate that MdGRF11 acts as a positive regulator of salt and drought stress responses through regulating ROS scavenging and other signaling systems.

Global Transcriptome and Co-Expression Network Analysis Reveal Contrasting Response of Japonica and Indica Rice Cultivar to γ Radiation

Japonica and indica are two important subspecies in cultivated Asian rice. Irradiation is a classical approach to induce mutations and create novel germplasm. However, little is known about the differential response between japonica and indica rice after γ radiation. Here, we utilized the RNA sequencing and Weighted Gene Co-expression Network Analysis (WGCNA) to compare the transcriptome differences between japonica Nipponbare (NPB) and indica Yangdao6 (YD6) in response to irradiation. Japonica subspecies are more sensitive to irradiation than the indica subspecies. Indica showed a higher seedling survival rate than japonica. Irradiation caused more extensive DNA damage in shoots than in roots, and the severity was higher in NPB than in YD6. GO and KEGG pathway analyses indicate that the core genes related to DNA repair and replication and cell proliferation are similarly regulated between the varieties, however the universal stress responsive genes show contrasting differential response patterns in japonica and indica. WGCNA identifies 37 co-expressing gene modules and ten candidate hub genes for each module. This provides novel evidence indicating that certain peripheral pathways may dominate the molecular networks in irradiation survival and suggests more potential target genes in breeding for universal stress tolerance in rice.

Meta-analysis of the effects of overexpression of WRKY transcription factors on plant responses to drought stress

BACKGROUND

The tryptophan-arginine-lysine-tyrosine (WRKY) transcription factors play important roles in plants, allowing them to adapt to environmental conditions that are not normally conducive to plant growth; in particular, drought. There has been extensive research on WRKY transcription factors and the effects of their overexpression in plants on resistance to drought stress. However, due to the materials (the type and species of donor and receptor, promoters) and treatments (the type and time of stress) used, different and often confounding results have been obtained between studies. Meta-analysis is a powerful statistical tool that can be used to summarize results from numerous independent experiments on the same research topic while accounting for variability across experiments.

RESULTS

We carried out a meta-analysis of 16 measured parameters that affect drought resistance in plants overexpressing WRKY transcription factors and wild-type plants. We found that only one of these parameters was significantly different between transgenic and wild-type plants under drought and control conditions at a 95% confidence interval (p = 0.000, p = 0.009, respectively). Eleven of the sixteen parameters were obviously different in WRKY transgenic plants under drought and control conditions (SV, p = 0.023, SSC, p = 0.000, SOD, p = 0.012, SFW, p = 0.000, RL, p = 0.016, Pro, p = 0.000, POD, p = 0.027, MDA, p = 0.000, H2O2, p = 0.003, EL, p = 0.000, CHC, p = 0.000, respectively), seven of the eleven obviously different parameters showed positive effect (SSC, SOD, Pro, POD, MDA, H2O2, EL), four of them revealed negative effect (SV, SFW, RL, CHC).

CONCLUSION

We have found that only one of these parameters was significantly different between transgenic and wild-type plants under drought and control conditions respectively, at a 95% confidence interval. And eleven of sixteen parameters showed obviously different of WRKY-overexpressed plants under different conditions (water-stressed and normal), suggesting that WRKY transcription factors play an important role in plant responses to drought stress. These findings also provide a theoretical basis for further study of the role of WRKY transcription factors in the regulation of plant responses to environmental stress.