Introgression of SbERD4 Gene Encodes an Early-Responsive Dehydration-Stress Protein That Confers Tolerance against Different Types of Abiotic Stresses in Transgenic Tobacco

The positive impact of the NtTAS14-like1 gene on osmotic stress response in Nicotiana tabacum

KEY MESSAGE

NtTAS14-like1 enhances osmotic tolerance through coordinately activating the expression of osmotic- and ABA-related genes. Osmotic stress is one of the most important limiting factors for tobacco (Nicotiana tabacum) growth and development. Dehydrin proteins are widely involved in plant adaptation to osmotic stress, but few of these proteins have been functionally characterized in tobacco. Here, to identify genes required for osmotic stress response in tobacco, an encoding dehydrin protein gene NtTAS14-like1 was isolated based on RNA sequence data. The expression of NtTAS14-like1 was obviously induced by mannitol and abscisic acid (ABA) treatments. Knock down of NtTAS14-like1 expression reduced osmotic tolerance, while overexpression of NtTAS14-like1 conferred tolerance to osmotic stress in transgenic tobacco plants, as determined by physiological analysis of the relative electrolyte leakage and malonaldehyde accumulation. Further expression analysis by quantitative real-time PCR indicated that NtTAS14-like1 participates in osmotic stress response possibly through coordinately activating osmotic- and ABA-related genes expression, such as late embryogenesis abundant (NtLEA5), early responsive to dehydration 10C (NtERD10C), calcium-dependent protein kinase 2 (NtCDPK2), ABA-responsive element-binding protein (NtAREB), ABA-responsive element-binding factor 1 (NtABF1), dehydration-responsive element-binding genes (NtDREB2A), xanthoxin dehydrogenase/reductase (NtABA2), ABA-aldehyde oxidase 3 (NtAAO3), 9-cis-epoxycarotenoid dioxygenase (NtNCED3). Together, this study will facilitate to improve our understandings of molecular and functional properties of plant TAS14 proteins and to improve genetic evidence on the involvement of the NtTAS14-like1 in osmotic stress response of tobacco.

Evolution of the 14-3-3 gene family in monocotyledons and dicotyledons and validation of MdGRF13 function in transgenic Arabidopsis thaliana

KEY MESSAGE

The 14-3-3 family is more highly conserved among monocotyledons, and overexpression of MdGRF13 improved drought and salt tolerance in transgenic Arabidopsis thaliana. The 14-3-3 are highly conserved regulatory proteins found in eukaryotes and play an essential role in plant growth, development and stress response. However, the 14-3-3 gene family evolution in monocotyledons and dicotyledons and the biological functions of the MdGRF13 under abiotic stress remain unknown. In our study, 195 members of the 14-3-3 family were identified from 12 species and divided into ε group and the Non-ε group. Synteny analysis within the 14-3-3 family indicated that segmental duplication events contributed to the expansion of the family. Selective pressure analysis indicated that purifying selection was a vital force in the 14-3-3 genes evolution, and monocotyledons had a lower million years ago (Mya) mean values than dicotyledons. Meanwhile, the codon adaptation index (CAI) and frequency of optical codons (FOP) are higher and the effective number of codons (Nc) is lower in monocotyledons 14-3-3 genes compared to dicotyledons. Moreover, the yeast two-hybrid (Y2H) demonstrated that MdGRF13 interacts with MdRD22, MdLHP1a and MdMORF1. Significantly, the malondialdehyde (MDA) content and relative conductivity were decreased, while the superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities were increased in transgenic Arabidopsis compared to the wild type (WT) under drought and salt stress. These results suggest that overexpression of MdGRF13 significantly improved the tolerance to drought and salt stress in transgenic Arabidopsis. Thus, our results provide a theoretical basis for exploring the evolution and function of the 14-3-3 gene family in monocotyledons and dicotyledons.

Genome-Wide Characterization and Function Analysis of ZmERD15 Genes' Response to Saline Stress in Zea mays L

Early responsive dehydration (ERD) genes can be rapidly induced by dehydration. ERD15 genes have been confirmed to regulate various stress responses in plants. However, the maize ERD15 members have not been characterized. In the present study, a total of five ZmERD15 genes were identified from the maize genome and named ZmERD15a, ZmERD15b, ZmERD15c, ZmERD15d, and ZmERD15e. Subsequently, their protein properties, gene structure and duplication, chromosomal location, cis-acting elements, subcellular localization, expression pattern, and over-expression in yeast were analyzed. The results showed that the ZmERD15 proteins were characterized by a similar size (113-159 aa) and contained a common domain structure, with PAM2 and adjacent PAE1 motifs followed by an acidic region. The ZmERD15 proteins exhibited a close phylogenetic relationship with OsERD15s from rice. Five ZmERD15 genes were distributed on maize chromosomes 2, 6, 7, and 9 and showed a different exon-intron organization and were expanded by duplication. Besides, the promoter region of the ZmERD15s contained abundant cis-acting elements that are known to be responsive to stress and hormones. Subcellular localization showed that ZmERD15b and ZmERD15c were localized in the nucleus. ZmERD15a and ZmERD15e were localized in the nucleus and cytoplasm. ZmERD15d was localized in the nucleus and cell membrane. The results of the quantitative real-time PCR (qRT-PCR) showed that the expression of the ZmERD15 genes was regulated by PEG, salinity, and ABA. The heterologous expression of ZmERD15a, ZmERD15b, ZmERD15c, and ZmERD15d significantly enhanced salt tolerance in yeast. In summary, a comprehensive analysis of ZmERD15s was conducted in the study. The results will provide insights into further dissecting the biological function and molecular mechanism of ZmERD15s regulating of the stress response in maize.

Integrated physiological and weighted gene co-expression network analysis reveals the hub genes engaged in nitrate-regulated alleviation of ammonium toxicity at the seedling stage in wheat (Triticum aestivum L.)

Wheat has a specific preference for NO₃ ^- and shows toxicity symptoms under high NH₄ ⁺ concentrations. Increasing the nitrate supply may alleviate ammonium stress. Nevertheless, the mechanisms underlying the nitrate regulation of wheat root growth to alleviate ammonium toxicity remain unclear. In this study, we integrated physiological and weighted gene co-expression network analysis (WGCNA) to identify the hub genes involved in nitrate alleviation of ammonium toxicity at the wheat seedling stage. Five NH₄ ⁺/NO₃ ^- ratio treatments, including 100/0 (N_a), 75/25 (N_r1), 50/50 (N_r2), 25/75 (N_r3), and 0/100 (N_n) were tested in this study. The results showed that sole ammonium treatment (N_a) increased the lateral root number but reduced root biomass. Increasing the nitrate supply significantly increased the root biomass. Increasing nitrate levels decreased abscisic acid (ABA) content and increased auxin (IAA) content. Furthermore, we identified two modules (blue and turquoise) using transcriptome data that were significantly related to root physiological growth indicators. TraesCS6A02G178000 and TraesCS2B02G056300 were identified as hub genes in the two modules which coded for plastidic ATP/ADP-transporter and WRKY62 transcription factors, respectively. Additionally, network analysis showed that in the blue module, TraesCS6A02G178000 interacts with downregulated genes that coded for indolin-2-one monooxygenase, SRG1, DETOXIFICATION, and wall-associated receptor kinase. In the turquoise module, TraesCS2B02G056300 was highly related to the genes that encoded ERD4, ERF109, CIGR2, and WD40 proteins, and transcription factors including WRKY24, WRKY22, MYB30, and JAMYB, which were all upregulated by increasing nitrate supply. These studies suggest that increasing the nitrate supply could improve root growth and alleviate ammonium toxicity through physiological and molecular regulation networks, including ROS, hormonal crosstalk, and transcription factors.

Identification of CAMTA Gene Family in Heimia myrtifolia and Expression Analysis under Drought Stress

Calmodulin-binding transcription factor (CAMTA) is an important component of plant hormone signal transduction, development, and drought resistance. Based on previous transcriptome data, drought resistance genes of the Heimia myrtifolia CAMTA transcription factor family were predicted in this study. The physicochemical characteristics of amino acids, subcellular localization, transmembrane structure, GO enrichment, and expression patterns were also examined. The results revealed that H. myrtifolia has a total of ten members (HmCAMTA1~10). Phylogenetic tree analysis of the HmCAMTA gene family revealed four different branches. The amino acid composition of CAMTA from H. myrtifolia and Punica granatum was quite similar. In addition, qRT-PCR data showed that the expression levels of HmCAMTA1, HmCAMTA2, and HmCAMTA10 genes increased with the deepening of drought, and the peak values appeared in the T4 treatment. Therefore, it is speculated that the above four genes are involved in the response of H. myrtifolia to drought stress. Additionally, HmCAMTA gene expression was shown to be more abundant in roots and leaves than in other tissues according to tissue-specific expression patterns. This study can be used to learn more about the function of CAMTA family genes and the drought tolerance response mechanism in H. myrtifolia.

Introgression of a novel gene AhBINR differentially expressed during PGPR Brachybacterium saurashtrense-Arachis hypogaea interaction enhances plant performance under nitrogen starvation and salt stress in tobacco

Plant growth-promoting rhizobacteria provide endurance during environmental stress conditions. Previously, we have shown that the interaction of the halotolerant diazotrophic bacteria Brachybacterium saurashtrense JG06 induces physio-biochemical and molecular changes in Arachis hypogaea under nitrogen starvation conditions. Here we deciphered the role of a novel gene AhBINR that was differentially overexpressed in A. hypogaea after interaction with B. saurashtrense JG06 under nitrogen deficit conditions. Overexpression of the AhBINR gene in the model plant (tobacco) showed higher growth parameters (root length, shoot length, fresh weight, and dry weight) under nitrogen starvation and salt stress in comparison to the wild type and vector control. Transgenic plants were enabled with a higher photosynthesis rate, which provides the support for better performance under N₂ starvation and salt stress. Results showed that the transgenic plants overexpressing the AhBINR gene had better physiological status and lower ROS accumulation under adverse conditions. Microarray transcriptome analysis showed that the transcription factors, biotic and abiotic stress, photosynthesis, and metabolism-related genes were differentially expressed (total 736 and 6530 genes were expressed under nitrogen deficit and salt stress conditions, respectively at a 5-fold change level) in comparison to wild type plants. Overall results showed the involvement of the AhBINR gene in the activation of the abiotic stress (nitrogen starvation and salt stress) related pathways, which can be overexpressed after legume-rhizobacterial interaction.

NtRAV4 negatively regulates drought tolerance in Nicotiana tabacum by enhancing antioxidant capacity and defence system

KEY MESSAGE

NtRAV4 is a nucleus-localised protein and no self-activation effect. ntrav4 mutants maintain the steady state of the ROS system under drought stress by enhancing antioxidant capacity and defence system. The APETALA2/ethylene response factor (AP2/ERF) transcription factor (TF) family plays an important role in plant responses to environmental stresses. In this study, we identified a novel NtRAV4 TF, a member of RAV subfamily among AP2/ERF gene family, which have AP2 and B3 domain in its N- and C-terminus, respectively. Subcellular localisation and self-activation activity analysis revealed that NtRAV4 localised in the nucleus and had no self-activation effect. The overexpression and gene editing vectors of NtRAV4 were constructed by homologous recombination and CRISPR/Cas9 gene editing methods, and transformed into tobacco by agrobacterium-mediated method. ntrav4 led to the appearance of termination codon in advance and lacked the unique B3 domain of RAV subfamily protein. Further analysis displayed that knockout of the NtRAV4 in tobacco increased drought tolerance with high relative water content, accompanied by reduced stomatal aperture, density, and stomatal opening ratio compared to overexpression lines and WT. Moreover, ntrav4 knockout plants also exhibited increased osmotic tolerance with low malondialdehyde (MDA) and ion leakage (EL), less accumulation of O2•- and H2O2, and high enzymatic antioxidant (SOD, POD, CAT) activities, non-enzymatic antioxidant (AsA-GSH cycle) contents and hormone (IAA, ABA, GA3, and ZR) levels under drought stress. Furthermore, ntrav4 mutants in tobacco improved the expression levels of ROS-related proline synthesis and stress-responsive genes under osmotic stress. Our results indicate that NtRAV4 negatively regulates plant tolerance to drought stress by reducing water loss and activating the antioxidant system and stress-related gene expression to maintain the steady state of the ROS system.

Differential Physio-Biochemical and Metabolic Responses of Peanut (Arachis hypogaea L.) under Multiple Abiotic Stress Conditions

The frequency and severity of extreme climatic conditions such as drought, salinity, cold, and heat are increasing due to climate change. Moreover, in the field, plants are affected by multiple abiotic stresses simultaneously or sequentially. Thus, it is imperative to compare the effects of stress combinations on crop plants relative to individual stresses. This study investigated the differential regulation of physio-biochemical and metabolomics parameters in peanut (Arachis hypogaea L.) under individual (salt, drought, cold, and heat) and combined stress treatments using multivariate correlation analysis. The results showed that combined heat, salt, and drought stress compounds the stress effect of individual stresses. Combined stresses that included heat had the highest electrolyte leakage and lowest relative water content. Lipid peroxidation and chlorophyll contents did not significantly change under combined stresses. Biochemical parameters, such as free amino acids, polyphenol, starch, and sugars, significantly changed under combined stresses compared to individual stresses. Free amino acids increased under combined stresses that included heat; starch, sugars, and polyphenols increased under combined stresses that included drought; proline concentration increased under combined stresses that included salt. Metabolomics data that were obtained under different individual and combined stresses can be used to identify molecular phenotypes that are involved in the acclimation response of plants under changing abiotic stress conditions. Peanut metabolomics identified 160 metabolites, including amino acids, sugars, sugar alcohols, organic acids, fatty acids, sugar acids, and other organic compounds. Pathway enrichment analysis revealed that abiotic stresses significantly affected amino acid, amino sugar, and sugar metabolism. The stress treatments affected the metabolites that were associated with the tricarboxylic acid (TCA) and urea cycles and associated amino acid biosynthesis pathway intermediates. Principal component analysis (PCA), partial least squares-discriminant analysis (PLS-DA), and heatmap analysis identified potential marker metabolites (pinitol, malic acid, and xylopyranose) that were associated with abiotic stress combinations, which could be used in breeding efforts to develop peanut cultivars that are resilient to climate change. The study will also facilitate researchers to explore different stress indicators to identify resistant cultivars for future crop improvement programs.