Over-expression of TaMYB33 encoding a novel wheat MYB transcription factor increases salt and drought tolerance in Arabidopsis

Overexpression of TdNACB improves the drought resistance of rice

Drought stress greatly affects disrupts the productivity, ecological structure, physiological and biochemical activities of wheat at different growth stages. However, drought stress tolerance is a complex quantitative trait and involves multiple metabolic pathways. We found that a wild emmer introgression line BAd7-209 had stronger drought resistance compared with drought resistant wheat Zhongmai 175. The transcriptome analysis found 14,284, 22,383 and 21,451 genes had expression corresponding responsed to drought stress at 24h, 48h, 120h, respectively and significantly enriched in 'Arginine and proline metabolism' and 'Peroxisome' in BAd7-209. 1666 transcription factors (TFs) related responsed to drought stress in which TdNACB showed high expression at 24h, 48h and 120h and had the closest relationship with TaNAC48 and OsNAC6 in phylogenetic analysis. Overexpression of TdNACB significantly enhanced drought resistance in rice and overexpression lines had significantly higher CAT, POD and SOD activity, Pro content and lower MDA content than those of the WT under drought stress. The result demonstrated that TdNACB positively regulates drought resistance through increasing proline content and enhancing activity of enzyme related to ROS scavenging. The results of this study provides candidate genes for improving wheat drought resistance and guide as reference for studying the molecular mechanisms of wheat drought resistance.

The cotton MYB33 gene is a hub gene regulating the trade-off between plant growth and defense in Verticillium dahliae infection

INTRODUCTION

Sessile plants engage in trade-offs between growth and defense capacity in response to fluctuating environmental cues. MYB is an important transcription factor that plays many important roles in controlling plant growth and defense. However, the mechanism behind how it keeps a balance between these two physiological processes is still largely unknown.

OBJECTIVES

Our work focuses on the dissection of the molecular mechanism by which GhMYB33 regulates plant growth and defense.

METHODS

The CRISPR/Cas9 technique was used to generate mutants for deciphering GhMYB33 functions. Yeast two-hybrid, luciferase complementary imaging, and co-immunoprecipitation assays were used to prove that proteins interact with each other. We used the electrophoretic mobility shift assay, yeast one-hybrid, and luciferase activity assays to analyze GhMYB33 acting as a promoter. A β-glucuronidase fusion reporter and 5' RNA ligase mediated amplification of cDNA ends analysis showed that ghr-miR319c directedly cleaved the GhMYB33 mRNA.

RESULTS

Overexpressing miR319c-resistant GhMYB33 (rGhMYB33) promoted plant growth, accompanied by a significant decline in resistance against Verticillium dahliae. Conversely, its knockout mutant, ghmyb33, demonstrated growth restriction and concomitant augmentation of V. dahliae resistance. GhMYB33 was found to couple with the DELLA protein GhGAI1 and bind to the specific cis-elements of GhSPL9 and GhDFR1 promoters, thereby modulating internode elongation and plant resistance in V. dahliae infection. The ghr-miR319c was discovered to target and suppress GhMYB33 expression. The overexpression of ghr-miR319c led to enhanced plant resistance and a simultaneous reduction in plant height.

CONCLUSION

Our findings demonstrate that GhMYB33 encodes a hub protein and controls the expression of GhSPL9 and GhDFR1, implicating a pivotal role for the miR319c-MYB33 module to regulate the trade-offs between plant growth and defense.

MaMYBR30, a Novel 1R-MYB, Plays Important Roles in Plant Development and Abiotic Stress Resistance

The V-myb myeloblastosis viral oncogene homolog (MYB) family participate in various bioprocesses including development and abiotic stress responses. In the present study, we first report a 1R SHAQKYF-class MYB, MaMYBR30, in mulberry. Subcellular localization and sequence analysis indicated MaMYBR30 is located in the nucleus and belongs to a CCA-like subgroup with a conserved SHAQKYF motif. Expression profile analysis showed that MaMYBR30 is expressed in leaves and can be induced by drought and salt stress. The down-regulation of MaMYBR30 using virus-induced gene silence (VIGS) in mulberry and the overexpression of MaMYBR30 in Arabidopsis were induced to explore the function of MaMYBR30. The functional characterization of MaMYBR30 in vivo indicated that MaMYBR30 can positively regulate the resistance of mulberry to drought while negatively regulating the resistance of mulberry to salt stress. In addition, MaMYBR30 also affects flower development and reproductive growth, especially after exposure to salt stress. Weighted gene co-expression network analysis (WGCNA) primarily revealed the possible genes and signal pathways that are regulated by MaMYBR30. Our results also imply that complex molecular mechanisms mediated by MaMYBR30, including crosstalk of ion toxicity, phytohormone signal transduction, flowering development, and epigenetic modification, need to be further explored in the future.

Insights into Salinity Tolerance in Wheat

Salt stress has a detrimental impact on food crop production, with its severity escalating due to both natural and man-made factors. As one of the most important food crops, wheat is susceptible to salt stress, resulting in abnormal plant growth and reduced yields; therefore, damage from salt stress should be of great concern. Additionally, the utilization of land in coastal areas warrants increased attention, given diminishing supplies of fresh water and arable land, and the escalating demand for wheat. A comprehensive understanding of the physiological and molecular changes in wheat under salt stress can offer insights into mitigating the adverse effects of salt stress on wheat. In this review, we summarized the genes and molecular mechanisms involved in ion transport, signal transduction, and enzyme and hormone regulation, in response to salt stress based on the physiological processes in wheat. Then, we surveyed the latest progress in improving the salt tolerance of wheat through breeding, exogenous applications, and microbial pathways. Breeding efficiency can be improved through a combination of gene editing and multiple omics techniques, which is the fundamental strategy for dealing with salt stress. Possible challenges and prospects in this process were also discussed.

The Impact of Salinity on Crop Yields and the Confrontational Behavior of Transcriptional Regulators, Nanoparticles, and Antioxidant Defensive Mechanisms under Stressful Conditions: A Review

One of the most significant environmental challenges to crop growth and yield worldwide is soil salinization. Salinity lowers soil solution water potential, causes ionic disequilibrium and specific ion effects, and increases reactive oxygen species (ROS) buildup, causing several physiological and biochemical issues in plants. Plants have developed biological and molecular methods to combat salt stress. Salt-signaling mechanisms regulated by phytohormones may provide additional defense in salty conditions. That discovery helped identify the molecular pathways that underlie zinc-oxide nanoparticle (ZnO-NP)-based salt tolerance in certain plants. It emphasized the need to study processes like transcriptional regulation that govern plants' many physiological responses to such harsh conditions. ZnO-NPs have shown the capability to reduce salinity stress by working with transcription factors (TFs) like AP2/EREBP, WRKYs, NACs, and bZIPs that are released or triggered to stimulate plant cell osmotic pressure-regulating hormones and chemicals. In addition, ZnO-NPs have been shown to reduce the expression of stress markers such as malondialdehyde (MDA) and hydrogen peroxide (H2O2) while also affecting transcriptional factors. Those systems helped maintain protein integrity, selective permeability, photosynthesis, and other physiological processes in salt-stressed plants. This review examined how salt stress affects crop yield and suggested that ZnO-NPs could reduce plant salinity stress instead of osmolytes and plant hormones.

Multi-Omic Analysis Reveals the Molecular Mechanism of UV-B Stress Resistance in Acetylated RcMYB44 in Rhododendron chrysanthum

Ultraviolet-B (UV-B) radiation is a significant environmental factor influencing the growth and development of plants. MYBs play an essential role in the processes of plant responses to abiotic stresses. In the last few years, the development of transcriptome and acetylated proteome technologies have resulted in further and more reliable data for understanding the UV-B response mechanism in plants. In this research, the transcriptome and acetylated proteome were used to analyze Rhododendron chrysanthum Pall. (R. chrysanthum) leaves under UV-B stress. In total, 2348 differentially expressed genes (DEGs) and 685 differentially expressed acetylated proteins (DAPs) were found. The transcriptome analysis revealed 232 MYB TFs; we analyzed the transcriptome together with the acetylated proteome, and screened 4 MYB TFs. Among them, only RcMYB44 had a complete MYB structural domain. To investigate the role of RcMYB44 under UV-B stress, a homology tree was constructed between RcMYB44 and Arabidopsis MYBs, and it was determined that RcMYB44 shares the same function with ATMYB44. We further constructed the hormone signaling pathway involved in RcMYB44, revealing the molecular mechanism of resistance to UV-B stress in R. chrysanthum. Finally, by comparing the transcriptome and the proteome, it was found that the expression levels of proteins and genes were inconsistent, which is related to post-translational modifications of proteins. In conclusion, RcMYB44 of R. chrysanthum is involved in mediating the growth hormone, salicylic acid, jasmonic acid, and abscisic acid signaling pathways to resist UV-B stress.

miRNAs for crop improvement

Climate change significantly impacts crop production by inducing several abiotic and biotic stresses. The increasing world population, and their food and industrial demands require focused efforts to improve crop plants to ensure sustainable food production. Among various modern biotechnological tools, microRNAs (miRNAs) are one of the fascinating tools available for crop improvement. miRNAs belong to a class of small non-coding RNAs playing crucial roles in numerous biological processes. miRNAs regulate gene expression by post-transcriptional target mRNA degradation or by translation repression. Plant miRNAs have essential roles in plant development and various biotic and abiotic stress tolerance. In this review, we provide propelling evidence from previous studies conducted around miRNAs and provide a one-stop review of progress made for breeding stress-smart future crop plants. Specifically, we provide a summary of reported miRNAs and their target genes for improvement of plant growth and development, and abiotic and biotic stress tolerance. We also highlight miRNA-mediated engineering for crop improvement and sequence-based technologies available for the identification of miRNAs associated with stress tolerance and plant developmental events.

Root and Leaf Anatomy, Ion Accumulation, and Transcriptome Pattern under Salt Stress Conditions in Contrasting Genotypes of Sorghum bicolor

Roots from salt-susceptible ICSR-56 (SS) sorghum plants display metaxylem elements with thin cell walls and large diameter. On the other hand, roots with thick, lignified cell walls in the hypodermis and endodermis were noticed in salt-tolerant CSV-15 (ST) sorghum plants. The secondary wall thickness and number of lignified cells in the hypodermis have increased with the treatment of sodium chloride stress to the plants (STN). Lignin distribution in the secondary cell wall of sclerenchymatous cells beneath the lower epidermis was higher in ST leaves compared to the SS genotype. Casparian thickenings with homogenous lignin distribution were observed in STN roots, but inhomogeneous distribution was evident in SS seedlings treated with sodium chloride (SSN). Higher accumulation of K⁺ and lower Na⁺ levels were noticed in ST compared to the SS genotype. To identify the differentially expressed genes among SS and ST genotypes, transcriptomic analysis was carried out. Both the genotypes were exposed to 200 mM sodium chloride stress for 24 h and used for analysis. We obtained 70 and 162 differentially expressed genes (DEGs) exclusive to SS and SSN and 112 and 26 DEGs exclusive to ST and STN, respectively. Kyoto Encyclopaedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analysis unlocked the changes in metabolic pathways in response to salt stress. qRT-PCR was performed to validate 20 DEGs in each SSN and STN sample, which confirms the transcriptomic results. These results surmise that anatomical changes and higher K⁺/Na⁺ ratios are essential for mitigating salt stress in sorghum apart from the genes that are differentially up- and downregulated in contrasting genotypes.

Genome-Wide Identification and Analysis of MYB Transcription Factor Family in Hibiscus hamabo

MYB transcription factors constitute one of the largest gene families in plants and play essential roles in the regulation of plant growth, responses to stress, and a wide variety of physiological and biochemical processes. In this study, 204 MYB proteins (HhMYBs) were identified in the Hibiscus hamabo Sieb. et Zucc (H. hamabo) genome and systematically analyzed based on their genomic sequence and transcriptomic data. The candidate HhMYB proteins and MYBs of Arabidopsis thaliana were divided into 28 subfamilies based on the analysis of their phylogenetic relationships and their motif patterns. Expression analysis using RNA-seq and quantitative real-time PCR (qRT-PCR) indicated that most HhMYBs are differentially regulated under drought and salt stresses. qRT-PCR analysis of seven selected HhMYBs suggested that the HhMYB family may have regulatory roles in the responses to stress and hormones. This study provides a framework for a more comprehensive analysis of the role of MYBs in the response to abiotic stress in H. hamabo.

CgMYB1, an R2R3-MYB transcription factor, can alleviate abiotic stress in an annual halophyte Chenopodium glaucum

MYB transcription factors (TFs) are important regulators of the stress response in plants. In the present study, we characterized the CgMYB1 gene in Chenopodium glaucum, a member of the R2R3-MYB TF family. CgMYB1 was located in the nucleus with an activating domain at the C terminus. The CgMYB1 gene could be induced by salt and cold stress in C. glaucum. Overexpressing CgMYB1 in Arabidopsis significantly enhanced salt and cold tolerance, probably by improving physiological performance and stress-related gene expression. Further analysis suggests that the positive response of CgMYB1 to abiotic stress may partially be attributed to the interaction between CgMYB1 and the CgbHLH001 promoter followed by activation of downstream stress-responsive genes, which mediates stress tolerance. Our findings should contribute to further understanding of the function of R2R3 MYB TF in response to abiotic stress.

Identification and Phylogenetic Analysis of the R2R3-MYB Subfamily in Brassica napus

The R2R3-MYB sub-family proteins are composed of most members of MYB (v-Myb avian myeloblastosis viral oncogene homolog) protein, a plant-specific transcription factor (TF) that is classified into four classes depending on the number of MYB repeats. R2R3-MYB TFs are involved in physiological and biochemical processes. However, the functions of the Brassica napus R2R3-MYB genes are still mainly unknown. In this study, 35 Brassica napus MYB (BnaMYB) genes were screened in the genome of Brassica napus, and details about their physical and chemical characteristics, evolutionary relationships, chromosome locations, gene structures, three-dimensional protein structures, cis-acting promoter elements, and gene duplications were uncovered. The BnaMYB genes have undergone segmental duplications and positive selection pressure, according to evolutionary studies. The same subfamilies have similar intron-exon patterns and motifs, according to the genes' structure and conserved motifs. Additionally, through cis-element analysis, many drought-responsive and other stress-responsive cis-elements have been found in the promoter regions of the BnaMYB genes. The expression of the BnaMYB gene displays a variety of tissue-specific patterns. Ten lignin-related genes were chosen for drought treatment. Our research screened four genes that showed significant upregulation under drought stress, and thus may be important drought-responsive genes. The findings lay a new foundation for understanding the complex mechanisms of BnaMYB in multiple developmental stages and pathways related to drought stress in rapeseed.

The wheat WRKY transcription factor TaWRKY1-2D confers drought resistance in transgenic Arabidopsis and wheat (Triticum aestivum L.)

The WRKY transcription factor family has been associated with a variety of plant biological processes, such as biotic and abiotic stress responses. In this study, 13 wheat TaWRKY DEGs in transcriptome data before and after drought stress, namely TaWRKY1 to TaWRKY8, including various copies, were identified and classified as Group I, II, or III. TaWRKY1-2D overexpression enhanced drought tolerance in transgenic Arabidopsis. Moreover, the AtRD29A, AtP5CS1, AtPOD1, AtCAT1, and AtSOD (Cu/Zn) genes, which are related to the stress response and antioxidant system, were significantly upregulated in TaWRKY1-2D transgenic Arabidopsis under drought stress. TaWRKY1-2 silencing in wheat increases the MDA content, reduces the contents of proline and chlorophyll and the activities of antioxidant enzymes, and inhibits the expression levels of antioxidant (TaPOD, TaCAT, and TaSOD (Fe))- and stress-related genes (TaP5CS) under drought stress. Yeast two-hybrid screening revealed TaDHN3 as an interaction partner of TaWRKY1-2D; their interaction was further confirmed using yeast two-hybrid and bimolecular fluorescence complementation. Furthermore, TaWRKY1-2D may play essential roles in wheat drought tolerance through posttranslational regulation of TaDHN3. Overall, these findings contribute to our knowledge of the WRKY family in wheat and identify TaWRKY1-2D as a promising candidate gene for improving wheat breeding to generate drought-tolerant wheat.

Identification of Glu-D1 Alleles and Novel Marker-Trait Associations for Flour Quality and Grain Yield Traits under Heat-Stress Environments in Wheat Lines Derived from Diverse Accessions of Aegilops tauschii

Heat stress during grain filling is considered one of the major abiotic factors influencing wheat grain yield and quality in arid and semi-arid regions. We studied the effect of heat stress on flour quality and grain yield at moderate and continuous heat stress under natural field conditions using 147 lines of wheat multiple synthetic derivatives (MSD) containing Aegilops tauschii introgressions. The study aimed to identify the marker-trait associations (MTAs) for the quality traits and grain yield under heat-stress conditions and identify stress-resilient germplasm-combining traits for good flour quality and grain yield. The MSD lines showed considerable genetic variation for quality traits and grain yield under heat-stress conditions; some lines performed better than the recurrent parent, Norin 61. We identified two MSD lines that consistently maintained relative performance (RP) values above 100% for grain yield and dough strength. We found the presence of three high-molecular-weight glutenin subunits (HMW-GSs) at the Glu-D1 locus derived from Ae. tauschii, which were associated with stable dough strength across the four environments used in this study. These HMW-GSs could be potentially useful in applications for future improvements of end-use quality traits targeting wheat under severe heat stress. A total of 19,155 high-quality SNP markers were used for the genome-wide association analysis and 251 MTAs were identified, most of them on the D genome, confirming the power of the MSD panel as a platform for mining and exploring the genes of Ae. tauschii. We identified the MTAs for dough strength under heat stress, which simultaneously control grain yield and relative performance for dough strength under heat-stress/optimum conditions. This study proved that Ae. tauschii is an inexhaustible resource for genetic mining, and the identified lines and pleiotropic MTAs reported in this study are considered a good resource for the development of resilient wheat cultivars that combine both good flour quality and grain yield under stress conditions using marker-assisted selection.

An R2R3-MYB transcription factor VyMYB24, isolated from wild grape Vitis yanshanesis J. X. Chen., regulates the plant development and confers the tolerance to drought

In grapevines, the MYB transcription factors play an important regulatory role in the phenylpropanoid pathway including proanthocyanidin, anthocyanin, and flavonoid biosynthesis. However, the role of MYB in abiotic stresses is not clear. In this study, an R2R3-MYB transcription factor, VyMYB24, was isolated from a high drought-tolerant Chinese wild Vitis species V. yanshanesis. Our findings demonstrated that it was involved in plant development and drought tolerance. VyMYB24 is a nuclear protein and is significantly induced by drought stress. When over-expressed in tobacco, VyMYB24 caused plant dwarfing including plant height, leaf area, flower size, and seed weight. The GA1+3 content in transgenic plants was reduced significantly, and spraying exogenous gibberellin could recover the dwarf phenotype of VyMYB24 transgenic plants, suggesting that VyMYB24 might inhibit plant development by the regulation of gibberellin (GA) metabolism. Under drought stress, the VyMYB24 transgenic plants improved their tolerance to drought with a lower wilting rate, lower relative electrical conductivity, and stronger roots. Compared to wild-type tobacco plants, VyMYB24 transgenic plants accumulated less reactive oxygen, accompanied by increased antioxidant enzyme activity and upregulated gene expression levels of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) genes. In addition, transgenic plants accumulated more proline, and their related synthetic genes NtP5CR and NtP5CS genes were significantly upregulated when exposed to drought. Besides, abiotic stress-responsive genes, NtDREB, NtERD10C, NtERD10D, and NtLEA5, were upregulated significantly in VyMYB24 transgenic plants. These results indicate that VyMYB24 plays a positive regulatory role in response to drought stress and also regulates plant development, which provides new evidence to further explore the molecular mechanism of drought stress of the MYB gene family.

2D-DIGE based proteome analysis of wheat-Thinopyrum intermedium 7XL/7DS translocation line under drought stress

Background

Drought stress is the most limiting factor for plant growth and crop production worldwide. As a major cereal crop, wheat is susceptible to drought. Thus, discovering and utilizing drought-tolerant gene resources from related species are highly important for improving wheat drought resistance. In this study, the drought tolerance of wheat Zhongmai 8601-Thinopyrum intermedium 7XL/7DS translocation line YW642 was estimated under drought stress, and then two-dimensional difference gel electrophoresis (2D-DIGE) based proteome analysis of the developing grains was performed to uncover the drought-resistant proteins.

Results

The results showed that 7XL/7DS translocation possessed a better drought-tolerance compared to Zhongmai 8601. 2D-DIGE identified 146 differential accumulation protein (DAP) spots corresponding to 113 unique proteins during five grain developmental stages of YW642 under drought stress. Among them, 55 DAP spots corresponding to 48 unique proteins displayed an upregulated expression, which were mainly involved in stress/defense, energy metabolism, starch metabolism, protein metabolism/folding and transport. The cis-acting element analysis revealed that abundant stress-related elements were present in the promoter regions of the drought-responsive protein genes, which could play important roles in drought defense. RNA-seq and RT-qPCR analyses revealed that some regulated DAP genes also showed a high expression level in response to drought stress.

Conclusions

Our results indicated that Wheat-Th. intermedium 7XL/7DS translocation line carried abundant drought-resistant proteins that had potential application values for wheat drought tolerance improvement.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08599-1.

Eutrema EsMYB90 Gene Improves Growth and Antioxidant Capacity of Transgenic Wheat Under Salinity Stress

The ectopic expression of the EsMYB90 transcription factor gene from halophytic Eutrema salsugineum has been reported to enhance the level of anthocyanin and other flavonoid metabolites in transgenic tobacco. In this study, the wheat JW1 overexpressing EsMYB90 showed longer roots and higher fresh weight than that in wild type (WT) under salt stress. In addition, the transgenic wheat plants displayed significantly higher peroxidase (POD) and glutathione S-transferase (GST) activity, as well as markedly lower malondialdehyde (MDA) content than that of the WT during salt stress conditions. The analysis of histochemical staining and H₂O₂ level indicated that the accumulation of reactive oxygen species (ROS) was significantly lower in the roots of transgenic wheat plants compared to the WT under salt stress. Transcriptome analysis revealed that the EsMYB90 gene affected the expression of considerable amounts of stress-related genes that were involved in phenylpropanoid biosynthesis and antioxidant activity in transgenic plants subjected to NaCl treatment. Importantly, the significantly upregulated expression genes in transgenic wheat under salt stress were mainly associated with the antioxidative enzymes POD and GST encoding genes compared with the WT. Furthermore, EsMYB90 is suggested to bind with the MYB-binding elements of pTaANS2 and pTaDFR1 by dual luciferase assay, to activate the transcription of TaANS2 and TaDFR1 genes that are encoding key enzymes of anthocyanin biosynthesis in transgenic wheat plants. All the results indicated that, under salt stress, the EsMYB90 gene plays a crucial role in preventing wheat seedlings from oxidative stress damage via enhancing the accumulation of non-enzymatic flavonoids and activities of antioxidative enzymes, which suggested that EsMYB90 is an ideal candidate gene for the genetic engineering of crops.

Systematic Analysis and Identification of Drought-Responsive Genes of the CAMTA Gene Family in Wheat (Triticum aestivum L.)

The calmodulin-binding transcription activator (CAMTA) is a Ca²⁺/CaM-mediated transcription factor (TF) that modulates plant stress responses and development. Although the investigations of CAMTAs in various organisms revealed a broad range of functions from sensory mechanisms to physiological activities in crops, little is known about the CAMTA family in wheat (Triticum aestivum L.). Here, we systematically analyzed phylogeny, gene expansion, conserved motifs, gene structure, cis-elements, chromosomal localization, and expression patterns of CAMTA genes in wheat. We described and confirmed, via molecular evolution and functional verification analyses, two new members of the family, TaCAMTA5-B.1 and TaCAMTA5-B.2. In addition, we determined that the expression of most TaCAMTA genes responded to several abiotic stresses (drought, salt, heat, and cold) and ABA during the seedling stage, but it was mainly induced by drought stress. Our study provides considerable information about the changes in gene expression in wheat under stress, notably that drought stress-related gene expression in TaCAMTA1b-B.1 transgenic lines was significantly upregulated under drought stress. In addition to providing a comprehensive view of CAMTA genes in wheat, our results indicate that TaCAMTA1b-B.1 has a potential role in the drought stress response induced by a water deficit at the seedling stage.

CYP81A68 confers metabolic resistance to ALS and ACCase-inhibiting herbicides and its epigenetic regulation in Echinochloa crus-galli

Long-term and excessive herbicide use has led to some environmental concerns and especially, herbicide resistance evolution in weeds. Here, we confirmed acetolactate synthase (ALS) inhibiting herbicide penoxsulam resistance and cross resistance to acetyl-coenzyme carboxylase (ACCase) inhibiting herbicides (cyhalofop-butyl and metamifop) in a global weed Echinochloa crus-galli population resistant to these herbicides (R). Penoxsulam metabolism study indicated that degradation rate was significantly higher in R than susceptible E. crus-galli population (S). RNA-sequencing revealed that a cytochrome P450 (P450) gene, CYP81A68, expressed higher in R versus S. Rice seedlings overexpressing this CYP81A68 gene are resistant to penoxsulam, cyhalofop-butyl and metamifop, and penoxsulam resistance is due to enhanced metabolism via O-demethylation. Deletion analysis of the CYP81A68 gene promoter identified an efficient region, in which differential methylation of CpG islands occurred between R and S. Collectively, these results demonstrate that upregulation of E. crus-galli CYP81A68 gene endows generalist metabolic resistance to commonly used ALS- and ACCase-inhibiting herbicides in rice fields and epigenetic regulation may play a role in the resistance evolution. This research could contribute to strategies reducing herbicide environmental impacts by judicious selection of alternative herbicide and non-chemical control tactics.

The GhMYB36 transcription factor confers resistance to biotic and abiotic stress by enhancing PR1 gene expression in plants

Drought and Verticillium wilt disease are two main factors that limit cotton production, which necessitates the identification of key molecular switch to simultaneously improve cotton resistance to Verticillium dahliae and tolerance to drought stress. R2R3-type MYB proteins could play such a role because of their conserved functions in plant development, growth, and metabolism regulation, however, till date a MYB gene conferring the desired resistance to both biotic and abiotic stresses has not been found in cotton. Here, we describe the identification of GhMYB36, a gene encoding a R2R3-type MYB protein in Gossypium hirsutum, which confers drought tolerance and Verticilium wilt resistance in both Arabidopsis and cotton. GhMYB36 was highly induced by PEG-simulated drought stress in G. hirsutum. GhMYB36-silenced cotton plants were more sensitive to both drought stress and Verticillium wilt. GhMYB36 overexpression in transgenic Arabidopsis and cotton plants gave rise to improved drought tolerance and Verticillium wilt resistance. Transient expression of fused GhMYB36-GFP in tobacco cells was able to localize GhMYB36 in the cell nucleus. In addition, RNA-seq analysis together with qRT-PCR validation in transgenic Arabidopsis overexpressing GhMYB36 revealed significantly enhanced PR1 expression. Luciferase interaction assays indicated that GhMYB36 are probably bound to the promoter of PR1 to activate its expression and the interaction, which was further verified by Yeast one hybrid assay. Taken together, our results suggest that GhMYB36 functions as a transcription factor that is involved in drought tolerance and Verticillium wilt resistance in Arabidopsis and cotton by enhancing PR1 expression.

Silencing of SlMYB55 affects plant flowering and enhances tolerance to drought and salt stress in tomato

The transcription factors of the MYB family are involved in plant growth and development and responses to biotic and abiotic stresses. Here, we isolated the R2R3-MYB transcription factor gene SlMYB55 and found that it is responsive to abscisic acid (ABA), drought, and salt stress. Notably, the expression levels of multiple stress-related and inflorescence and flowering time-related genes were changed in SlMYB55-RNAi plants compared to wild-type plants. Transient tobacco expression experiments indicated that SlMYB55 directly targets the WUS and 4CL genes to regulate the development of inflorescence and flavonoid biosynthesis. Yeast two-hybrid experiments showed that the SlMYB55 protein interacts with the MADS-box family protein MBP21. Based on these results, we concluded that SlMYB55 affects the biosynthesis of ABA, regulates drought and salt responses through ABA-mediated signal transduction pathways, and directly or indirectly affects the expression of genes related to drought and salt response, flowering time, sepal size and inflorescence, thereby regulating stress tolerance and flower development. In summary, this study identified essential roles for SlMYB55 in regulating drought and salt tolerance and flower development.

Effects of Low Temperature Stress on Source-Sink Organs in Wheat and Phosphorus Mitigation Strategies

The 21st century presents many challenges to mankind, including climate change, fast growing human population, and serious concerns over food security. Wheat is a leading cereal crop that largely fulfills the global food needs. Low temperature stress accompanied by nutrient-starved soils is badly disrupting the source-sink relationship of wheat, thus causing an acute decline in final yield and deteriorating the grain quality. This review paper aimed to understand how low temperature stress affects wheat source-sink organs (i.e., leaves, roots, and spikes) and how phosphorus application reliefs in alleviating its harmful consequences. Also, we discussed mitigation strategies to enhance wheat capacity to adapt to varying temperature extremes and made rational recommendations based on modern agronomic and breeding approaches. Therefore, this study is likely to establish a solid foundation for improving the tolerance to low temperature stress and to improve its phosphorus utilization efficiency in wheat.

Genome-wide profiling of drought-tolerant Arabidopsis plants over-expressing chickpea MT1 gene reveals transcription factors implicated in stress modulation

Drought, a major abiotic limiting factor, could be modulated with in-built reprogramming of plants at molecular level by regulating the activity of plant developmental processes, stress endurance and adaptation. The transgenic Arabidopsis thaliana over-expressing metallothionein 1 (MT1) gene of desi chickpea (Cicer arietinum L.) was subjected to transcriptome analysis. We evaluated drought tolerance of 7 days old plants of Arabidopsis thaliana in both wild-type (WT) as well as transgenic plants and performed transcriptome analysis. Our analysis revealed 24,737 transcripts representing 24,594 genes out of which 5,816 were differentially expressed genes (DEGs) under drought conditions and 841 genes were common in both genotypes. A total of 1251 DEGs in WT and 2099 in MT1 were identified in comparison with control. Out of the significant DEGs, 432 and 944 were upregulated, whereas 819 and 1155 were downregulated in WT and MT1 plants, respectively. The physiological and molecular parameters involving germination assay, root length measurements under different stress treatments and quantitative expression analysis of transgenic plants in comparison to wild-type were found to be enhanced. CarMT1 plants also demonstrated modulation of various other stress-responsive genes that reprogrammed themselves for stress adaptation. Amongst various drought-responsive genes, 24 DEGs showed similar quantitative expression as obtained through RNA sequencing data. Hence, these modulatory genes could be used as a genetic tool for understanding and delineating the mechanisms for fine-tuning of stress responses in crop plants.

R2R3-MYB Transcription Factor PlMYB108 Confers Drought Tolerance in Herbaceous Peony (Paeonia lactiflora Pall.)

The MYB transcription factor (TF) is crucial for plant growth, development, and response to abiotic stress, but it is rarely reported in the herbaceous peony (Paeonia lactiflora Pall.). Here, an MYB TF gene was isolated, and based on our prior mRNA data from P. lactiflora samples, it was treated with drought stress (DS). Its complete cDNA structure was 1314 bp, which encoded 291 amino acids (aa). Furthermore, using sequence alignment analysis, we demonstrated that PlMYB108 was an R2R3-MYB TF. We also revealed that PlMYB108 was primarily localized in the nucleus. Its levels rose during DS, and it was positively correlated with drought tolerance (DT) in P. lactiflora. In addition, when PlMYB108 was overexpressed in tobacco plants, the flavonoid content, antioxidant enzyme activities, and photosynthesis were markedly elevated. Hence, the transgenic plants had stronger DT with a higher leaf water content and lower H2O2 accumulation compared to the wild-type (WT) plants. Based on these results, PlMYB108 is a vital gene that serves to increase flavonoid accumulation, reactive oxygen species (ROS), scavenging capacity, and photosynthesis to confer DT. The results would provide a genetic resource for molecular breeding to enhance plant DT.

Genome-Wide Identification and Expression Analysis of MYB Transcription Factor Superfamily in Dendrobium catenatum

Dendrobium catenatum is an important traditional Chinese medicine and naturally grows on tree trunks and cliffs, where it can encounter diverse environmental stimuli. MYB transcription factors are widely involved in response to abiotic stresses. However, the MYB gene family has not yet been systematically cataloged in D. catenatum. In this study, a total of 133 MYB proteins were identified in D. catenatum, including 32 MYB-related, 99 R2R3-MYB, 1 3R-MYB, and 1 4R-MYB proteins. Phylogenetic relationships, conserved motifs, gene structures, and expression profiles in response to abiotic stresses were then analyzed. Phylogenetic analysis revealed MYB proteins in D. catenatum could be divided into 14 subgroups, which was supported by the conserved motif compositions and gene structures. Differential DcMYB gene expression and specific responses were analyzed under drought, heat, cold, and salt stresses using RNA-seq and validated by qRT-PCR. Forty-two MYB genes were differentially screened following exposure to abiotic stresses. Five, 12, 11, and 14 genes were specifically expressed in response to drought, heat, cold, and salt stress, respectively. This study identified candidate MYB genes with possible roles in abiotic tolerance and established a theoretical foundation for molecular breeding of D. catenatum.

Modulation of NF-YB genes in Ricinus communis L. in response to different temperatures and developmental stages and functional characterization of RcNF-YB8 as an important regulator of flowering time in Arabidopsis thaliana

We have characterized the NF-YB gene family in R. communis using bioinformatics, ecotopic expression, and transcriptomics. A total of 14 RcNF-YB genes were identified in R. communis genome using the conserved NF-YB region. This number is similar to what is found in A. thaliana (13 genes) and O. sativa (11 genes), whereas it is considerably lower to what is found in P. trichocarpa (21 genes) and S. lycopersycum (29 genes). Several regulatory cis-elements were identified in the promoter region, including low temperature, defense and stress, MIC, MYB, and abscisic acid. RcNF-YB is strongly modulated by temperature and it is dependent on the stage of germination. In general, RcNF-YB genes showed higher expression levels in dry seeds and early imbibition (EI) samples as compared to later stages of seedling development. Ectopic expression of RcNF-YB8 reduced flowering time in Arabidopsis reducing the time required for the formation of the first visible bud, the time required to open the first flower, and the time required for the formation of the first visible silique. At the end of the life cycle, ectopic expression of RcNF-YB8 affected plant height (PH), silique length (SL), the total number of silique per plant, 1000-seed weight, and seed size. Our data demonstrated the role of RcNF-YB8 in flowering time, plant height and seed production, and it shows that it may constitute a key target gene for breeding superior R. communis genotypes.

PtrMYB3, a R2R3-MYB Transcription Factor from Poncirus trifoliata, Negatively Regulates Salt Tolerance and Hydrogen Peroxide Scavenging

MYB transcription factors are widely present in plants and play significant roles in abiotic stresses. However, most MYB genes have not been identified in plants and their functions in abiotic stresses are still unknown. In this study, one MYB gene, designated as PtrMYB3, was cloned from trifoliate orange (Poncirus trifoliata (L.) Raf.), and its function in salt tolerance was investigated. PtrMYB3 contains a conserved R2R3-MYB domain, which is the typical property of R2R3-MYB subfamily proteins. Expression profiling under abiotic stresses indicated that PtrMYB3 could be induced by salt, dehydration and cold stresses. PtrMYB3 was found to be localized to the nucleus and possessed transactivation activity. Overexpression of PtrMYB3 by genetic transformation in tobacco impaired its salt tolerance, whereas silencing of PtrMYB3 by VIGS (virus-induced gene silencing) in trifoliate orange conferred significantly enhanced salt tolerance, indicating that PtrMYB3 negatively regulates salt tolerance. Furthermore, a peroxidase gene (PtrPOD) was found to be greatly upregulated in PtrMYB3-silenced trifoliate orange, and a dual LUC (luciferase) assay confirmed that PtrMYB3 could suppress the expression of PtrPOD. The hydrogen peroxide (H₂O₂) accumulation in PtrMYB3 transgenic tobacco plants after salt stress was higher than the wild type (WT), further confirming that overexpression of PtrMYB3 inhibited PtrPOD-mediated H₂O₂ scavenging. Taken together, these results demonstrate that PtrMYB3 negatively regulates salt tolerance, at least in part, due to the excess accumulation of H₂O₂.

Genome-wide analysis of MYB transcription factors of Vaccinium corymbosum and their positive responses to drought stress

Background

Blueberry (Vaccinium corymbosum L.) is an important species with a high content of flavonoids in fruits. As a perennial shrub, blueberry is characterized by shallow-rooted property and susceptible to drought stress. MYB transcription factor was reported to be widely involved in plant response to abiotic stresses, however, the role of MYB family in blueberry responding to drought stress remains elusive.

Results

In this study, we conducted a comprehensive analysis of VcMYBs in blueberry based on the genome data under drought stress, including phylogenetic relationship, identification of differentially expressed genes (DEGs), expression profiling, conserved motifs, expression correlation and protein-protein interaction prediction, etc. The results showed that 229 non-redundant MYB sequences were identified in the blueberry genome, and divided into 23 subgroups. A total of 102 MYB DEGs with a significant response to drought stress were identified, of which 72 in leaves and 69 in roots, and 8 differential expression genes with a > 20-fold change in the level of expression. 17 DEGs had a higher expression correlation with other MYB members. The interaction partners of the key VcMYB proteins were predicted by STRING analysis and in combination with physiological and morphological observation. 10 key VcMYB genes such as VcMYB8, VcMYB102 and VcMYB228 were predicted to be probably involved in reactive oxygen species (ROS) pathway, and 7 key VcMYB genes (VcMYB41, VcMYB88 and VcMYB100, etc..) probably participated in leaf regulation under drought treatment.

Conclusions

Our studies provide a new understanding of the regulation mechanism of VcMYB family in blueberry response to drought stress, and lay fundamental support for future studies on blueberry grown in regions with limited water supply for this crop.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07850-5.

Cold Stress in Wheat: Plant Acclimation Responses and Management Strategies

Unpredicted variability in temperature is associated with frequent extreme low-temperature events. Wheat is a leading crop in fulfilling global food requirements. Climate-driven temperature extremes influence the vegetative and reproductive growth of wheat, followed by a decrease in yield. This review describes how low temperature induces a series of modifications in the morphophysiological, biochemical, and molecular makeup of wheat and how it is perceived. To cope with these modifications, crop plants turn on their cold-tolerance mechanisms, characterized by accumulating soluble carbohydrates, signaling molecules, and cold tolerance gene expressions. The review also discusses the integrated management approaches to enhance the performance of wheat plants against cold stress. In this review, we propose strategies for improving the adaptive capacity of wheat besides alleviating risks of cold anticipated with climate change.

Genome-wide analysis of MYB transcription factors and their responses to salt stress in Casuarina equisetifolia

BACKGROUND

MYB transcription factors are a kind of DNA binding protein that can specifically interact with the promoter region. Members of MYB TFs are widely involved in plant growth and development, secondary metabolism, stress response, and hormone signal transduction. However, there is no report of comprehensive bioinformatics analysis on the MYB family of Casuarina equisetifolia.

RESULTS

In this study, bioinformatics methods were used to screen out 182 MYB transcription factors from the Casuarina equisetifolia genome database, including 69 1R-MYB, 107 R2R3-MYB, 4 R1R2R3-MYB, and 2 4R-MYB. The C. equisetifolia R2R3-MYB genes were divided into 29 groups based on the phylogenetic topology and the classification of the MYB superfamily in Arabidopsis thaliana, while the remaining MYB genes (1R-MYB, R1R2R3-MYB, and 4R-MYB) was divided into 19 groups. Moreover, the conserved motif and gene structure analysis shown that the members of the CeqMYBs were divided into the same subgroups with mostly similar gene structures. In addition, many conserved amino acids in the R2 and R3 domains of CeqMYBs by WebLogo analysis, especially tryptophan residues (W), with 3 conserved W in R2 repeat and 2 conserved W in R3 repeat. Combining promoter and GO annotation analysis, speculated on the various biological functions of CeqMYBs, thus 32 MYB genes were selected to further explore its response to salt stress by using qPCR analysis technique. Most CeqMYB genes were differentially regulated following multiple salt treatments.

CONCLUSIONS

Seven genes (CeqMYB164, CeqMYB4, CeqMYB53, CeqMYB32, CeqMYB114, CeqMYB71 and CeqMYB177) were assigned to the "response to salt stress" by GO annotation. Among them, the expression level of CeqMYB4 was up-regulated under various salt treatments, indicating CeqMYB4 might participated in the response to salt stress. Our results provide important information for the biological function of C. equisetifolia, as well as offer candidate genes for further study of salt stress mechanism.

FvMYB24, a strawberry R2R3-MYB transcription factor, improved salt stress tolerance in transgenic Arabidopsis

Salinity is one of the major environmental stresses that limit crop growth and productivity. In this study, the FvMYB24 gene that encodes an R2R3-type MYB transcription factor was cloned and characterized. An expression analysis showed that FvMYB24 had a tissue- and stage-specific profile and was induced by salt treatment. Arabidopsis plants that overexpressed transgenic FvMYB24 exhibited a higher germination rate, fresh weight, chlorophyll content, and longer root length than the wild type (WT) under salt stress. The transgenic plants had higher activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) and the accumulation of proline, while these plants accumulated lower amounts of malondialdehyde (MDA) compared with the WT. Furthermore, our results also revealed that the overexpression of FvMYB24 up-regulated the expression of several stress-related genes (AtSOS1, AtSOS2, AtSOS3, AtSOD, AtPOD, AtCAT1, AtNHX1, and AtLEA3) in response to salt stress, thus, enhancing the tolerance of transgenic Arabidopsis. An analysis of the cis-acting elements in the SOS1, SOS2, and SOS3 promoters revealed MYB-binding sites. However, FvMYB24 could only bind to the SOS1 promoter to mediate salt tolerance but not to the SOS2 and SOS3 promoters. These findings suggest that FvMYB24 could potentially be used as a positive regulator in transgenic plant breeding to improve the tolerance of strawberry plants to salt.

One Hundred Candidate Genes and Their Roles in Drought and Salt Tolerance in Wheat

Drought and salinity are major constraints to agriculture. In this review, we present an overview of the global situation and the consequences of drought and salt stress connected to climatic changes. We provide a list of possible genetic resources as sources of resistance or tolerant traits, together with the previous studies that focused on transferring genes from the germplasm to cultivated varieties. We explained the morphological and physiological aspects connected to hydric stresses, described the mechanisms that induce tolerance, and discussed the results of the main studies. Finally, we described more than 100 genes associated with tolerance to hydric stresses in the Triticeae. These were divided in agreement with their main function into osmotic adjustment and ionic and redox homeostasis. The understanding of a given gene function and expression pattern according to hydric stress is particularly important for the efficient selection of new tolerant genotypes in classical breeding. For this reason, the current review provides a crucial reference for future studies on the mechanism involved in hydric stress tolerance and the use of these genes in mark assistance selection (MAS) to select the wheat germplasm to face the climatic changes.

Transcriptome analysis reveals differentially expressed MYB transcription factors associated with silicon response in wheat

Silicon plays a vital role in plant growth. However, molecular mechanisms in response to silicon have not previously been studied in wheat. In this study, we used RNA-seq technology to identify differentially expressed genes (DEGs) in wheat seedlings treated with silicon. Results showed that many wheat genes responded to silicon treatment, including 3057 DEGs, of which 6.25% (191/3057) were predicted transcription factors (TFs). Approximately 14.67% (28 out of 191) of the differentially expressed TFs belonged to the MYB TF family. Gene ontology (GO) enrichment showed that the highly enriched DEGs were responsible for secondary biosynthetic processes. According to KEGG pathway analysis, the DEGs were related to chaperones and folding catalysts, phenylpropanoid biosynthesis, and protein processing in the endoplasmic reticulum. Moreover, 411 R2R3-MYB TFs were identified in the wheat genome, all of which were classified into 15 groups and accordingly named S1–S15. Among them, 28 were down-regulated under silicon treatment. This study revealed the essential role of MYB TFs in the silicon response mechanism of plants, and provides important genetic resources for breeding silicon-tolerant wheat.

Genome-Wide Mining of MYB Transcription Factors in the Anthocyanin Biosynthesis Pathway of Gossypium Hirsutum

The MYB family, one of the largest transcription factor (TF) families, plays an important role in plant growth, development, and stress response. Although genome-wide analysis of the MYB family has been performed in many species based on sequence similarity, predicting the potential functions of the MYB genes and classifying the regulators into specific metabolic pathways remains difficult. In this study, using a hidden Markov model search and co-expression regulatory network analysis, we demonstrated a process to screen and identify potential MYB TFs in the anthocyanin biosynthesis pathway of Gossypium hirsutum. As a result, we identified 617 and 784 MYB genes (812 in total) from the previously reported and recently released genomes, respectively. Using 126 structural genes involved in the anthocyanin biosynthesis pathway as targets for several co-expression network analyses, we sorted out 31 R2R3-MYB genes, which are potential regulators in the specific pathway. Phylogenetic and collinearity analyses indicated that 83.9% of the 31 MYB genes originated from whole genome duplication or polyploidization. In addition, we revealed relatively specific regulatory relationships between the MYB TFs and their target structural genes. Approximately, 71% of the MYBs could regulate only a single anthocyanin-related structural gene. Moreover, we found that the A- and D- subgenome homoeologs of MYB TFs in G. hirsutum rarely co-regulate the same target gene. The current study not only demonstrated an easy method to rapidly predict potential TFs in a specific metabolic pathway, but also enhanced our understanding of the evolution, gene characteristics, expression, and regulatory pattern of MYB TFs in G. hirsutum.

Identification of Differentially Expressed Drought-Responsive Genes in Guar [Cyamopsis tetragonoloba (L.) Taub]

Drought remains one of the most serious environmental stresses because of the continuous reduction in soil moisture, which requires the improvement of crops with features such as drought tolerance. Guar [Cyamopsis tetragonoloba (L.) Taub], a forage and industrial crop, is a nonthirsty plant. However, the information on the transcriptome changes that occur under drought stress in guar is very limited; therefore, a gene expression analysis is necessary in this context. Here, we studied the differentially expressed genes (DEGs) in response to drought stress and their metabolic pathways. RNA-Seq via an expectation-maximization algorithm was used to estimate gene abundance. Subsequently, an Empirical Analysis of Digital Gene Expression Data in the R Bioconductor package was used to identify DEGs. Blast2GO, InterProScan, and the Kyoto Encyclopedia of Genes and Genomes were used to explore functional annotation, protein analysis, enzymes, and metabolic pathways. Transcription factors were identified using the PlantTFDB database. Our study identified 499 upregulated and 191 downregulated genes in response to drought stress. Of those, 32 upregulated and six downregulated genes were deemed as novel genes exclusive to guar. An aggregate of 137 protein families, 306 domains, 12 repeats, and two sites were upregulated. The proton-dependent oligopeptide transporter family and transferase, aquaporin transporter, calcium/calmodulin-dependent/calcium-dependent protein kinase, aspartic peptidase A1 family, UDP-glucuronosyl/UDP-glucosyltransferase, and major intrinsic protein were the most upregulated protein families. The upregulated unigenes were associated with 88 enzymes and 77 KEGG pathways. Finally, the MYB-related, MYB, and ERF transcription factor families were upregulated. These data may be useful for understanding the plant molecular response to drought stress.

Over-expression of rice R1-type MYB transcription factor confers different abiotic stress tolerance in transgenic Arabidopsis

Among various abiotic stresses, water deficit hit the first in the list followed by heavy metal stresses as a serious environmental growth-limiting factor that restricts the global crop yield. Molecular approaches will help us to trace key regulators which are involved in stress-related phenomenon to enhance crop productivity. The present study functionally characterized one of the key regulators, OsMYB-R1 in Arabidopsis. Phylogenetic analyses indicated that OsMYB-R1 had a close relationship with Sorghum bicolour and Zea mays. Ectopic expression of OsMYB-R1 in Arabidopsis resulted in improved tolerance to PEG/drought and chromium stress in addition to conferring no tolerance to salinity stress. Further RNA seq. data revealed that OsMYB-R1 regulates the expression of key genes that improve the root architecture and maintain the cellular homeostasis of transgenic lines through an efficient anti-oxidant system. It also reveals the differential gene expression of stress-responsive and hormone-responsive genes, which indicate the intricate network of defense regulatory machinery activated in transgenic lines. Additionally, salicylic acid (SA) plays a significant role in promoting the growth of the OsMYB-R1 over-expressing plants and increased GUS intensity in SA treated OsMYB-R1 promoter plants demonstrate the explicit role of SA signaling in overcoming stress tolerance. Whereas no significant change was observed in OsMYB-R1 over-expressing plants after ABA and MeJA treatment. Overall, OsMYB-R1 is a promising gene resource for improving abiotic stress tolerance in other crops, especially in dicotyledon plants.

Auxin-salicylic acid cross-talk ameliorates OsMYB-R1 mediated defense towards heavy metal, drought and fungal stress

The MYB TF family is an immensely large and functionally diverse class of proteins involved in the regulation of cell cycle, cell morphogenesis to stress signaling mechanism. The present study deciphered the hormonal cross-talk of wound inducible and stress-responsive OsMYB-R1 transcription factor in combating abiotic [Cr(VI) and drought/PEG] as well as biotic (Rhizoctonia solani) stress. OsMYB-R1 over-expressing rice transgenics exhibit a significant increase in lateral roots, which may be associated with increased tolerance under Cr(VI) and drought exposure. In contrast, its loss-of-function reduces stress tolerance. Higher auxin accumulation in the OsMYB-R1 over-expressed lines further strengthens the protective role of lateral roots under stress conditions. RNA-seq. data reveals over-representation of salicylic acid signaling molecule calcium-dependent protein kinases, which probably activate the stress-responsive downstream genes (Peroxidases, Glutathione S-transferases, Osmotins, Heat Shock Proteins, Pathogenesis Related-Proteins). Enzymatic studies further confirm OsMYB-R1 mediated robust antioxidant system as catalase, guaiacol peroxidase and superoxide dismutase activities were found to be increased in the over-expressed lines. Our results suggest that OsMYB-R1 is part of a complex network of transcription factors controlling the cross-talk of auxin and salicylic acid signaling and other genes in response to multiple stresses by modifying molecular signaling, internal cellular homeostasis and root morphology.

Drought tolerance in Triticum aestivum L. genotypes associated with enhanced antioxidative protection and declined lipid peroxidation

Drought is one of the major constraints in wheat production and causes a huge loss at grain-filling stage. In this study we highlighted the response of different wheat genotypes under drought stress at the grain-filling stage. Field experiments were conducted to evaluate 72 wheat (Triticum aestivum L.) genotypes under two water regimes: irrigated and drought condition. Four wheat genotypes, two each of drought tolerant (IC36761A, IC128335) and drought-susceptible category (IC335732 and IC138852) were selected on the basis of agronomic traits and drought susceptibility index (DSI), to understand their morphological, biochemical and molecular basis of drought stress tolerance. Among agronomic traits, productive tillers followed by biomass had high percent reduction under drought stress, thus drought stress had a great impact. Antioxidant activity (AO), total phenolic and proline content were found to be significantly higher in IC128335 genotype. Differential expression pattern of transcription factors of ten genes revealed that transcription factor qTaWRKY2 followed by qTaDREB, qTaEXPB23 and qTaAPEX might be utilized for developing wheat varieties resistant to drought stress. Understanding the role of TFs would be helpful to decipher the molecular mechanism involved in drought stress. Identified genotypes (IC128335 and IC36761A) may be useful as parental material for future breeding program to generate new drought-tolerant varieties.

Comparative Transcriptome Analysis Reveals Molecular Defensive Mechanism of Arachis hypogaea in Response to Salt Stress

Abiotic stresses comprise all nonliving factors, such as soil salinity, drought, extreme temperatures, and metal toxicity, posing a serious threat to agriculture and affecting the plant production around the world. Peanut (Arachis hypogaea L.) is one of the most important crops for vegetable oil, proteins, minerals, and vitamins in the world. Therefore, it is of importance to understand the molecular mechanism of peanut against salt stress. Six transcriptome sequencing libraries including 24-hour salt treatments and control samples were constructed from the young leaves of peanut. A comprehensive analysis between two groups detected 3,425 differentially expressed genes (DEGs) including 2,013 upregulated genes and 1,412 downregulated genes. Of these DEGs, 141 transcription factors (TFs) mainly consisting of MYB, AP2/ERF, WRKY, bHLH, and HSF were identified in response to salinity stress. Further, GO categories of the DEGs highly related to regulation of cell growth, cell periphery, sustained external encapsulating structure, cell wall organization or biogenesis, antioxidant activity, and peroxidase activity were significantly enriched for upregulated DEGs. The function of downregulated DEGs was mainly enriched in regulation of metabolic processes, oxidoreductase activity, and catalytic activity. Fourteen DEGs with response to salt tolerance were validated by real-time PCR. Taken together, the identification of DEGs' response to salt tolerance of cultivated peanut will provide a solid foundation for improving salt-tolerant peanut genetic manipulation in the future.

SlMYB102, an R2R3-type MYB gene, confers salt tolerance in transgenic tomato

Salinity threatens the productivity of tomato (Solanum lycopersicum L.). R2R3-type MYB transcription factors are important regulators in response to environmental stress. Here, we analyzed the function of the tomato R2R3-type MYB gene SlMYB102. A transcriptional activation assay showed that SlMYB102 had transactivation activity in yeast. Promoter analysis showed that multiple stress-related elements were found in the promoter of SlMYB102. Furthermore, SlMYB102 was induced by osmotic stress, particularly by salt stress. The overexpression of SlMYB102 in tomato affected multiple parameters under salinity stress. Under long-term salt stress, the degree of growth inhibition was significantly reduced in the two overexpression (OE) lines. In addition, the two OE lines maintained a better K⁺/Na⁺ ratio, lower reactive oxygen species (ROS) generation (O₂^•- production rate and H₂O₂ content) and lower electrolytic leakage rates than the wild type (WT). The activity of ROS scavenging enzymes including superoxide dismutase, peroxidase, catalase and ascorbate peroxidase, and the accumulation of antioxidants (ascorbic acid and glutathione) and proline was higher in the two OE lines compared with WT. The qRT-PCR analysis confirmed that the transcript abundance of many salt stress-related genes (SlSOS1, SlSOS2, SlNHX3, SlNHX4, SlHAK5, SlCPK1 and SlCPK3) was upregulated in two OE lines under salt stress. Collectively, these results suggest that SlMYB102 participates in tomato tolerance through the regulation of a series of molecular and physiological processes.

The Soybean bZIP Transcription Factor Gene GmbZIP2 Confers Drought and Salt Resistances in Transgenic Plants

Abiotic stresses, such as drought and salt, are major environmental stresses, affecting plant growth and crop productivity. Plant bZIP transcription factors (bZIPs) confer stress resistances in harsh environments and play important roles in each phase of plant growth processes. In this research, 15 soybean bZIP family members were identified from drought-induced de novo transcriptomic sequences of soybean, which were unevenly distributed across 12 soybean chromosomes. Promoter analysis showed that these 15 genes were rich in ABRE, MYB and MYC cis-acting elements which were reported to be involved in abiotic stress responses. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis indicated that 15 GmbZIP genes could be induced by drought and salt stress. GmbZIP2 was significantly upregulated under stress conditions and thus was selected for further study. Subcellular localization analysis revealed that the GmbZIP2 protein was located in the cell nucleus. qRT-PCR results show that GmbZIP2 can be induced by multiple stresses. The overexpression of GmbZIP2 in Arabidopsis and soybean hairy roots could improve plant resistance to drought and salt stresses. The result of differential expression gene analysis shows that the overexpression of GmbZIP2 in soybean hairy roots could enhance the expression of the stress responsive genes GmMYB48, GmWD40, GmDHN15, GmGST1 and GmLEA. These results indicate that soybean bZIPs played pivotal roles in plant resistance to abiotic stresses.

Functional activation of a novel R2R3-MYB protein gene, GmMYB68, confers salt-alkali resistance in soybean (Glycine max L.)

Soil salinity significantly reduces soybean (Glycine max L.) production worldwide. Plants resistance to stress conditions is a complex characteristic regulated by multiple signaling pathways. The v-Myb avian myeloblastosis viral oncogene homolog (MYB) transcription factor (TF) plays a crucial role in plant development, secondary metabolism, and abiotic stress responses. GmMYB68-overexpression and RNA interference (RNAi) lines were established for examining the function of G. max GmMYB68 in plant responses to abiotic stresses. The predicted amino acid sequence of GmMYB68 was similar to that of R2R3-MYB proteins. Quantitative real-time PCR analysis revealed that GmMYB68 expression varied in response to abiotic stresses. GmMYB68-overexpression lines showed enhanced resistance to salt and alkali stresses and their osmotic adjustment and photosynthetic rates were also stronger than that of GmMYB68-RNAi and wild type plants. Although wild type and transgenic plants showed no significant differences in agronomic traits under normal conditions, the overexpression of GmMYB68 increased grain number and 100-grain weights under salt stress. Our study identified a valuable TF associated with stress response in soybean, as its overexpression might help improve salt and alkali tolerance in soybean and other crops.

A MYB-related transcription factor from sheepgrass, LcMYB2, promotes seed germination and root growth under drought stress

BACKGROUND

Drought is one of the most serious factors limiting plant growth and production. Sheepgrass can adapt well to various adverse conditions, including drought. However, during germination, sheepgrass young seedlings are sensitive to these adverse conditions. Therefore, the adaptability of seedlings is very important for plant survival, especially in plants that inhabit grasslands or the construction of artificial grassland.

RESULTS

In this study, we found a sheepgrass MYB-related transcription factor, LcMYB2 that is up-regulated by drought stress and returns to a basal level after rewatering. The expression of LcMYB2 was mainly induced by osmotic stress and was localized to the nucleus. Furthermore, we demonstrate that LcMYB2 promoted seed germination and root growth under drought and ABA treatments. Additionally, we confirmed that LcMYB2 can regulate LcDREB2 expression in sheepgrass by binding to its promoter, and it activates the expression of the osmotic stress marker genes AtDREB2A, AtLEA14 and AtP5CS1 by directly binding to their promoters in transgenic Arabidopsis.

CONCLUSIONS

Based on these results, we propose that LcMYB2 improves plant drought stress tolerance by increasing the accumulation of osmoprotectants and promoting root growth. Therefore, LcMYB2 plays pivotal roles in plant responses to drought stress and is an important candidate for genetic manipulation to create drought-resistant crops, especially during seed germination.

MdMYB46 could enhance salt and osmotic stress tolerance in apple by directly activating stress-responsive signals

To expand the cultivation area of apple (Malus×domestica Borkh.) and select resistant varieties by genetic engineering, it is necessary to clarify the mechanism of salt and osmotic stress tolerance in apple. The MdMYB46 transcription factor was identified, and the stress treatment test of MdMYB46-overexpressing and MdMYB46-RNAi apple lines indicated that MdMYB46 could enhance the salt and osmotic stress tolerance in apple. In transgenic Arabidopsis and apple, MdMYB46 promoted the biosynthesis of secondary cell wall and deposition of lignin by directly binding to the promoter of lignin biosynthesis-related genes. To explore whether MdMYB46 could coordinate stress signal transduction pathways to cooperate with the formation of secondary walls to enhance the stress tolerance of plants, MdABRE1A, MdDREB2A and dehydration-responsive genes MdRD22 and MdRD29A were screened out for their positive correlation with osmotic stress, salt stress and the transcriptional level of MdMYB46. The further verification test demonstrated that MdMYB46 could activate their transcription by directly binding to the promoters of these genes. The above results indicate that MdMYB46 could enhance the salt and osmotic stress tolerance in apple not only by activating secondary cell wall biosynthesis pathways, but also by directly activating stress-responsive signals.

MYB Gene Family in Potato (Solanum tuberosum L.): Genome-Wide Identification of Hormone-Responsive Reveals Their Potential Functions in Growth and Development

As an important nongrain crop, the growth and yield of potato (Solanum tuberosum L.) is often affected by an unfavorable external environment in the process of cultivation. The MYB family is one of the largest and most important gene families, participating in the regulation of plant growth and development and response to abiotic stresses. Several MYB genes in potato that regulate anthocyanin synthesis and participate in abiotic stress responses have been identified. To identify all Solanum tuberosum L. MYB (StMYB) genes involved in hormone or stress responses to potentially regulate potato growth and development, we identified the MYB gene family at the genome-wide level. In this work, 158 StMYB genes were found in the potato genome. According to the amino acid sequence of the MYB domain and gene structure, the StMYB genes were divided into R2R3-MYB and R1R2R3-MYB families, and the R2R3-MYB family was divided into 20 subgroups (SGs). The expression of 21 StMYB genes from different SGs in roots, stems, leaves, flowers, shoots, stolons, young tubers, and mature tubers was determined by quantitative real-time polymerase chain reaction (qRT-PCR). The expression patterns of StMYB genes in potatoes treated with abscisic acid (ABA), indole-3-acetic acid (IAA), gibberellin acid 3 (GA3), NaCl, mannitol, and heat were also measured. We have identified several potential candidate genes that regulate the synthesis of potato flavonoids or participate in hormone or stress responses. This work provides a comprehensive understanding of the MYB family in potato and will lay a foundation for the future investigation of the potential functions of StMYB genes in the growth and development of potato.

Functional Analysis of the Marigold (Tagetes erecta) Lycopene ε-cyclase (TeLCYe) Promoter in Transgenic Tobacco

Lycopene ε-cyclases (LCYEs) are key enzymes in carotenoid biosynthesis converting red lycopene to downstream lutein. The flowers of marigold (Tagetes erecta) have been superior sources to supply lutein. However, the transcriptional regulatory mechanisms of LCYe in lutein synthesis are still unclear in marigold. In this work, the expression pattern of the TeLCYe gene in marigold indicated that TeLCYe mainly expressed in floral organs. To gain a better understanding of the expression and regulatory mechanism of TeLCYe gene, the TeLCYe promoter was isolated, sequenced, and analyzed through bioinformatics tools. The results suggested that the sequence of TeLCYe promoter contained various putative cis-acting elements responsive to exogenous and endogenous factors. The full-length TeLCYe promoter and three 5'-deletion fragments were fused to the GUS reporter gene and transferred into tobacco to test the promoter activities. A strong GUS activity was observed in stems of seedlings, leaves of seedlings, middle stems, top leaves, petals, stamens, and stigmas in transgenic tobacco containing full-length TeLCYe promoter LP0-2086. Deletion of - 910 to - 429 bp 5' to ATG significantly increased the GUS activity in chloroplast-rich tissues and floral organs, while deletion occurring from 1170 to 910 bp upstream ATG decreased the TeLCYe promoter strength in stems of seedlings, leaves of seedlings, top leaves and sepals. Functional characterization of the full-length TeLCYe promoter and its' deletion fragments in stable transgenic tobacco indicated that the LP0-2086 contains some specific cis-acting elements, which might result in the high-level expression of in floral organs, and LP2-910 might contain some specific cis-acting elements which improved GUS activities in vegetable tissues.

Expression of miR159 Is Altered in Tomato Plants Undergoing Drought Stress

In a scenario of global climate change, water scarcity is a major threat for agriculture, severely limiting crop yields. Therefore, alternatives are urgently needed for improving plant adaptation to drought stress. Among them, gene expression reprogramming by microRNAs (miRNAs) might offer a biotechnologically sound strategy. Drought-responsive miRNAs have been reported in many plant species, and some of them are known to participate in complex regulatory networks via their regulation of transcription factors involved in water stress signaling. We explored the role of miR159 in the response of Solanum lycopersicum Mill. plants to drought stress by analyzing the expression of sly-miR159 and its target SlMYB transcription factor genes in tomato plants of cv. Ailsa Craig grown in deprived water conditions or in response to mechanical damage caused by the Colorado potato beetle, a devastating insect pest of Solanaceae plants. Results showed that sly-miR159 regulatory function in the tomato plants response to distinct stresses might be mediated by differential stress-specific MYB transcription factor targeting. sly-miR159 targeting of SlMYB33 transcription factor transcript correlated with accumulation of the osmoprotective compounds proline and putrescine, which promote drought tolerance. This highlights the potential role of sly-miR159 in tomato plants’ adaptation to water deficit conditions.

A MYB-Related Transcription Factor from Lilium lancifolium L. (LlMYB3) Is Involved in Anthocyanin Biosynthesis Pathway and Enhances Multiple Abiotic Stress Tolerance in Arabidopsis thaliana

Most commercial cultivars of lily are sensitive to abiotic stresses. However, tiger lily (Lilium lancifolium L.), one of the most widely distributed wild lilies in Asia, has strong abiotic stresses resistance. Thus, it is indispensable to identify stress-responsive candidate genes in tiger lily for the stress resistance improvement of plants. In this study, a MYB related homolog (LlMYB3) from tiger lily was functionally characterized as a positive regulator in plant stress tolerance. LlMYB3 is a nuclear protein with transcriptional activation activity at C-terminus. The expression of LlMYB3 gene was induced by multiple stress treatments. Several stress-related cis-acting regulatory elements (MYBRS, MYCRS, LTRE and DRE/CRT) were located within the promoter of LlMYB3; however, the promoter activity was not induced sufficiently by various stresses treatments. Overexpressing LlMYB3 in Arabidopsis thaliana L. transgenic plants showed ABA hypersensitivity and enhanced tolerance to cold, drought, and salt stresses. Furthermore, we found LlMYB3 highly co-expressed with LlCHS2 gene under cold treatment; yeast one-hybrid (Y1H) assays demonstrated LlMYB3 was able to bind to the promoter of LlCHS2. These findings suggest that the stress-responsive LlMYB3 may be involved in anthocyanin biosynthesis pathway to regulate stress tolerance of tiger lily.

Research advances of MYB transcription factors in plant stress resistance and breeding

Plants face various stresses during the growth and development processes. The specific transcription factors bind to the cis-acting elements upstream of the stress resistance genes, specifically regulating the expression of the gene in plants and increasing the adaptability of plants to environmental stress. The transcription factor-mediated gene expression regulatory networks play an important role in plant stress response pathways. MYB (v-myb avian myeloblastosis viral oncogene homolog) transcription factor is one of the largest members of the transcription factor family in plants. It participates and has a great influence on all aspects of plant growth and development. It plays an important role in plant secondary metabolic regulation, hormone and environmental factor responses, cell differentiation, organ morphogenesis, and cell cycle regulation. This review mainly introduces the characteristics, structure, and classification of MYB transcription factors, as well as the abiotic stress resistance to drought, salt, temperature, and other functions in breeding, and provides a reference for the research and utilization of transcription factors in the future.

Co-occurrence of Mild Salinity and Drought Synergistically Enhances Biomass and Grain Retardation in Wheat

In the present study we analyzed the responses of wheat to mild salinity and drought with special emphasis on the so far unclarified interaction of these important stress factors by using high-throughput phenotyping approaches. Measurements were performed on 14 genotypes of different geographic origin (Austria, Azerbaijan, and Serbia). The data obtained by non-invasive digital RGB imaging of leaf/shoot area reflect well the differences in total biomass measured at the end of the cultivation period demonstrating that leaf/shoot imaging can be reliably used to predict biomass differences among different cultivars and stress conditions. On the other hand, the leaf/shoot area has only a limited potential to predict grain yield. Comparison of gas exchange parameters with biomass accumulation showed that suppression of CO2 fixation due to stomatal closure is the principal cause behind decreased biomass accumulation under drought, salt and drought plus salt stresses. Correlation between grain yield and dry biomass is tighter when salt- and drought stress occur simultaneously than in the well-watered control, or in the presence of only salinity or drought, showing that natural variation of biomass partitioning to grains is suppressed by severe stress conditions. Comparison of yield data show that higher biomass and grain yield can be expected under salt (and salt plus drought) stress from those cultivars which have high yield parameters when exposed to drought stress alone. However, relative yield tolerance under drought stress is not a good indicator of yield tolerance under salt (and salt plus drought) drought stress. Harvest index of the studied cultivars ranged between 0.38 and 0.57 under well watered conditions and decreased only to a small extent (0.37-0.55) even when total biomass was decreased by 90% under the combined salt plus drought stress. It is concluded that the co-occurrence of mild salinity and drought can induce large biomass and grain yield losses in wheat due to synergistic interaction of these important stress factors. We could also identify wheat cultivars, which show high yield parameters under the combined effects of salinity and drought demonstrating the potential of complex plant phenotyping in breeding for drought and salinity stress tolerance in crop plants.

Expression of the maize MYB transcription factor ZmMYB3R enhances drought and salt stress tolerance in transgenic plants

MYB proteins are major transcription factors that play significant roles in plant defenses against various stresses. However, available information regarding stress-related MYB genes in maize is minimal. Herein, a maize MYB gene, ZmMYB3R, was cloned and functionally characterized. Subcellular localisation analysis showed that ZmMYB3R is localised to the nucleus. Yeast one-hybrid results revealed that ZmMYB3R has trans-activation activity, and a minimal activation domain at the C-terminus spanning residues 217-563. Gene expression analysis suggested that ZmMYB3R was induced by drought, salt and abscisic acid (ABA). Transgenic Arabidopsis plants overexpressing ZmMYB3R displayed enhanced growth performance and higher survival rates, elevated catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) enzyme activities, increased sensitivity to ABA, and regulation of the stomatal aperture, suggesting that ZmMYB3R enhances tolerance to drought and salt stress. qRT-PCR assays revealed elevated expression levels of stress/ABA genes in transgenic plants following stress treatments. Moreover, transgenic plants accumulated higher ABA content than wild-type plants under drought and salt stress conditions. Collectively, these results indicate that ZmMYB3R is a positive transcription factor that enhances tolerance to drought and salt stress via an ABA-dependent pathway. The findings may prove useful for engineering economically important crops.