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

Apple MdZAT5 mediates root development under drought stress

Root plays an important role in plant drought tolerance, especially in horticultural crops like apples. However, the crucial regulator and molecular mechanism in root development of apple trees under drought are not well unknown. Cys2/His2-type Zinc-finger proteins are essential for plant response to drought, while the members of C2H2 Zinc-finger proteins in apple are largely unknown. In this study, we identified the members of the C1-2i subclass family of C2H2 Zinc-finger proteins in apple (Malus × domestica). Among them, MdZAT5 is significantly induced in apple roots under drought conditions and positively regulates apple root development under drought. Further investigation revealed that MdZAT5 positively regulates root development and root hydraulic conductivity by mediating the transcription level of MdMYB88 under drought stress. Taken together, our results demonstrate the importance of MdZAT5 in root development under drought in apple trees. This finding provides a new candidate direction for apple breeding for drought resistance.

Synergistic role of phenylpropanoid biosynthesis and citrate cycle pathways in heavy metal detoxification through secretion of organic acids

Excessive heavy metal contaminants in soils have serious ecological and environmental impacts, and affect plant growth and crop yields. Phytoremediation is an environmentally friendly means of lowering heavy metal concentrations in soils. In this study, we analyzed phenotypic and physiological traits, and the transcriptome and metabolome, of sheepgrass (Leymus chinensis) exposed to cadmium (Cd), lead (Pb), or zinc (Zn). Phenotypic and physiological analysis indicated that sheepgrass had strong tolerance to Cd/Pb/Zn. Transcriptomic analysis revealed that phenylpropanoid biosynthesis and organic acid metabolism were enriched among differentially expressed genes, and metabolomic analysis indicated that the citrate cycle was enriched in response to Cd/Pb/Zn exposure. Genes encoding enzymes involved in the phenylpropanoid and citrate cycle pathways were up-regulated under the Cd/Pb/Zn treatments. Organic acids significantly reduced heavy metal accumulation and improved sheepgrass tolerance of heavy metals. The results suggest that synergistic interaction of the phenylpropanoid and citrate cycle pathways in sheepgrass roots induced organic acid secretion to alleviate heavy metal toxicity. A cascade of enzymes involved in the interacting pathways could be targeted in molecular design breeding to enhance phytoremediation.

Re-watering solution facilitates seed germination and seedling growth of Carex schmidtii: Implication for species re-introduction in degraded semi-arid wetlands

Water deficiency threatens the health and function of wetlands in semi-arid areas. Optimum re-watering is an effective method for close-to-natural restoration to mitigate wetland degradation. Although the ecological importance of optimal re-watering as a nature-based solution for promoting wetland plant growth has been widely recognized, the response mechanisms of seed germination and seedling growth to re-watering are still poorly understood despite their decisive impact on plant life history. To fill this gap, this study compared the characteristics of seed germination and seedling growth in Carex schmidtii under initial water content with three levels (30%, 50%, and 70%) and five re-watering treatments (maintained at constant water content and re-watering to 100% on 7th, 14th, 21st, and 28th day). Moreover, the degree of reserve mobilization during four germination stages (seed suckering, sprouting, 20% germination, and seedling growth) was investigated. The results showed that water deficiency and re-watering treatments significantly affected C. schmidtii seed germination, seedling growth, and reserve mobilization. Compared with the other treatments, 50% moisture content and re-watering to 100% on the 14th day (50%-RT3) treatment significantly improved germination traits (germination rate, daily germination rate, germination index, and vigor index) and seedling growth characteristics (shoot length, root length, shoot biomass, root biomass, and total biomass). Furthermore, the degree of mobilization of starch, soluble protein, fat, and soluble sugar accumulation in C. schmidtii seeds under 50%-RT3 was higher than that in the other treatments. The structural equation model showed that the characteristics of seed germination and seedling growth of C. schmidtii were directly related to water deficiency and re-watering treatments, whereas reserve mobilization indirectly affected seed germination and seedling growth. These findings demonstrated that water deficiency and re-watering treatments have a crucial regulatory effect on seed germination and seedling growth of wetland plant species through a dual mechanism. This study provides information for the formulation of an optimum re-watering strategy for wetland vegetation restoration in semi-arid areas of the world.

Function of Transcription Factors PoMYB12, PoMYB15, and PoMYB20 in Heat Stress and Growth of Pleurotus ostreatus

MYB transcription factors (TFs) have been extensively studied in plant abiotic stress responses and growth and development. However, the role of MYB TFs in the heat stress response and growth and development of Pleurotus ostreatus remains unclear. To investigate the function of PoMYB12, PoMYB15, and PoMYB20 TFs in P. ostreatus, mutant strains of PoMYB12, PoMYB15, and PoMYB20 were generated using RNA interference (RNAi) and overexpression (OE) techniques. The results indicated that the mycelia of OE-PoMYB12, OE-PoMYB20, and RNAi-PoMYB15 mutant strains exhibited positive effects under heat stress at 32 °C, 36 °C, and 40 °C. Compared to wild-type strains, the OE-PoMYB12, OE-PoMYB20, and RNAi-PoMYB15 mutant strains promoted the growth and development of P. ostreatus. These mutant strains also facilitated the recovery of growth and development of P. ostreatus after 24 h of 36 °C heat stress. In conclusion, the expression of PoMYB12 and PoMYB20 supports the mycelium's response to heat stress and enhances the growth and development of P. ostreatus, whereas PoMYB15 produces the opposite effect.

Overexpression of a Grape MYB Transcription Factor Gene VhMYB2 Increases Salinity and Drought Tolerance in Arabidopsis thaliana

In viticulture, the highly resistant rootstock 'Beta' is widely used in Chinese grape production to avoid the effects of soil salinization and drought on grape growth. However, the mechanism of high resistance to abiotic stress in the 'Beta' rootstock is not clear. In this study, we demonstrated that VhMYB2 as a transcription factor made a significant contribution to salinity and drought stress, which was isolated from the 'Beta' rootstock. The coding sequence of the VhMYB2 gene was 858 bp, encoding 285 amino acids. The subcellular localization of VhMYB2 was located in the nucleus of tobacco epidermal cells. Moreover, RT-qPCR found that VhMYB2 was predominantly expressed in the mature leaf and root of the grape. Under salinity and drought stress, overexpressing VhMYB2 showed a higher resistant phenotype and survival rates in A. thaliana while the transgenic lines had a survival advantage by measuring the contents of proline, chlorophyll, and MDA, and activities of POD, SOD, and CAT, and expression levels of related stress response genes. The results reveal that VhMYB2 may be an important transcription factor regulating 'Beta' resistance in response to abiotic stress.

Comparative analysis of the MYB gene family in seven Ipomoea species

The MYB transcription factors regulate plant growth, development, and defense responses. However, information about the MYB gene family in Ipomoea species is rare. Herein, we performed a comprehensive genome-wide comparative analysis of this gene family among seven Ipomoea species, sweet potato (I. batatas), I. trifida, I. triloba, I. nil, I. purpurea, I. cairica, and I. aquatic, and identified 296, 430, 411, 291, 226, 281, and 277 MYB genes, respectively. The identified MYB genes were classified into five types: 1R-MYB (MYB-related), 2R-MYB (R2R3-MYB), 3R-MYB (R1R2R3-MYB), 4R-MYB, and 5R-MYB, and the MYB-related or R2R3-MYB type was the most abundant MYB genes in the seven species. The Ipomoea MYB genes were classed into distinct subgroups based on the phylogenetic topology and the classification of the MYB superfamily in Arabidopsis. Analysis of gene structure and protein motifs revealed that members within the same phylogenetic group presented similar exon/intron and motif organization. The identified MYB genes were unevenly mapped on the chromosomes of each Ipomoea species. Duplication analysis indicated that segmental and tandem duplications contribute to expanding the Ipomoea MYB genes. Non-synonymous substitution (Ka) to synonymous substitution (Ks) [Ka/Ks] analysis showed that the duplicated Ipomoea MYB genes are mainly under purifying selection. Numerous cis-regulatory elements related to stress responses were detected in the MYB promoters. Six sweet potato transcriptome datasets referring to abiotic and biotic stresses were analyzed, and MYB different expression genes' (DEGs') responses to stress treatments were detected. Moreover, 10 sweet potato MYB DEGs were selected for qRT-PCR analysis. The results revealed that four responded to biotic stress (stem nematodes and Ceratocystis fimbriata pathogen infection) and six responded to the biotic stress (cold, drought, and salt). The results may provide new insights into the evolution of MYB genes in the Ipomoea genome and contribute to the future molecular breeding of sweet potatoes.

Genome-Wide Identification and Characterization of Copper Chaperone for Superoxide Dismutase (CCS) Gene Family in Response to Abiotic Stress in Soybean

Copper Chaperone For Superoxide Dismutase (CCS) genes encode copper chaperone for Superoxide dismutase (SOD) and dramatically affect the activity of SOD through regulating copper delivery from target to SOD. SOD is the effective component of the antioxidant defense system in plant cells to reduce oxidative damage by eliminating Reactive oxygen species (ROS), which are produced during abiotic stress. CCS might play an important role in abiotic stress to eliminate the damage caused by ROS, however, little is known about CCS in soybean in abiotic stress regulation. In this study, 31 GmCCS gene family members were identified from soybean genome. These genes were classified into 4 subfamilies in the phylogenetic tree. Characteristics of 31 GmCCS genes including gene structure, chromosomal location, collinearity, conserved domain, protein motif, cis-elements, and tissue expression profiling were systematically analyzed. RT-qPCR was used to analyze the expression of 31 GmCCS under abiotic stress, and the results showed that 5 GmCCS genes(GmCCS5, GmCCS7, GmCCS8, GmCCS11 and GmCCS24) were significantly induced by some kind of abiotic stress. The functions of these GmCCS genes in abiotic stress were tested using yeast expression system and soybean hairy roots. The results showed that GmCCS7/GmCCS24 participated in drought stress regulation. Soybean hairy roots expressing GmCCS7/GmCCS24 showed improved drought stress tolerance, with increased SOD and other antioxidant enzyme activities. The results of this study provide reference value in-depth study CCS gene family, and important gene resources for the genetic improvement of soybean drought stress tolerance.

Transcriptome and metabolome analyses reveal novel insights into the seed germination of Michelia chapensis, an endangered species in China

Michelia chapensis Dandy, a well-known medicinal woody plant endemic to China, is endangered and seriously constricted by seed dormancy-induced low-regeneration in natural conditions. Cold stratification can effectively reduce seed dormancy and promote the seed germination of M. chapensis. However, the molecular events and systematic changes that occurred during seed germination in M. chapensis remain largely unknown. In this study, we carried out transcriptomic and metabolomic analyses to elucidate the potential molecular mechanisms underlying seed germination in M. chapensis under cold stratification. The results showed that the embryo cells became bigger and looser with increasing stratification time. Moreover, the endosperm appeared reduced due to the consumption of nutrients. Seventeen phytohormones were examined by the metabolome targeted for hormones. Compared with the ES (no stratification), the levels of indole-3-acetic acid (IAA) and gibberellin A₃ (GA₃) were increased in the MS (stratification for 45 days), while the abscisic acid (ABA) was downregulated in both MS and LS (stratification for 90 days). The transcriptome profiling identified 24975 differentially expressed genes (DEGs) in the seeds during germination. The seed germination of M. chapensis was mainly regulated by the biological pathways of plant hormone signal transduction, energy supply, secondary metabolite biosynthesis, photosynthesis-related metabolism, and transcriptional regulation. This study reveals the biological evidence of seed germination at the transcriptional level and provides a foundation for unraveling molecular mechanisms regulating the seed germination of M. chapensis.

A MYB-related transcription factor from peanut, AhMYB30, improves freezing and salt stress tolerance in transgenic Arabidopsis through both DREB/CBF and ABA-signaling pathways

Abiotic stresses such as salinity and low temperature have serious impact on peanut growth and yield. The present work investigated the function of a MYB-related transcription factor gene AhMYB30 obtained from peanut under salt and low temperature stresses by transgenic methods. The results indicated that the overexpression of AhMYB30 in Arabidopsis could enhance the resistance of transgenic plants to freezing and salt stresses. The expression of stress-response genes RD29A (Response-to-Dehydration 29A), COR15A (Cold-Regulated 15A), KIN1 (Kinesin 1) and ABI2 (Abscisic acid Insensitive 2) increased in transgenic plants compared with in wild-type. Subcellular localization and transcriptional autoactivation validation demonstrated that AhMYB30 has essential features of transcription factors. Therefore, AhMYB30 may increase salt and freezing stress tolerance as the transcription factor (TF) in Arabidopsis through both DREB/CBF and ABA-signaling pathways. Our results lay the theoretical foundation for exploring stress resistance mechanisms of peanut and offering novel genetic resources for molecular breeding.

Drought stress tolerance mechanisms and their potential common indicators to salinity, insights from the wild watermelon (Citrullus lanatus): A review

Climate change has escalated the effect of drought on crop production as it has negatively altered the environmental condition. Wild watermelon grows abundantly in the Kgalagadi desert even though the environment is characterized by minimal rainfall, high temperatures and intense sunshine during growing season. This area is also characterized by sandy soils with low water holding capacity, thus bringing about drought stress. Drought stress affects crop productivity through its effects on development and physiological functions as dictated by molecular responses. Not only one or two physiological process or genes are responsible for drought tolerance, but a combination of various factors do work together to aid crop tolerance mechanism. Various studies have shown that wild watermelon possess superior qualities that aid its survival in unfavorable conditions. These mechanisms include resilient root growth, timely stomatal closure, chlorophyll fluorescence quenching under water deficit as key physiological responses. At biochemical and molecular level, the crop responds through citrulline accumulation and expression of genes associated with drought tolerance in this species and other plants. Previous salinity stress studies involving other plants have identified citrulline accumulation and expression of some of these genes (chloroplast APX, Type-2 metallothionein), to be associated with tolerance. Emerging evidence indicates that the upstream of functional genes are the transcription factor that regulates drought and salinity stress responses as well as adaptation. In this review we discuss the drought tolerance mechanisms in watermelons and some of its common indicators to salinity at physiological, biochemical and molecular level.

Dehydration response in Stylosanthes scabra: Transcriptional, biochemical, and physiological modulations

Stylosanthes scabra, popularly known as stylo, is native to the Brazilian Caatinga semiarid region and stands out as a drought-tolerant shrub forage crop. This work provides information about the plant response during the first 48 h of water deficit, followed by a rehydration treatment. Besides root transcriptomics data, 13 physiological or biochemical parameters were scrutinized. Additionally, RNA-Seq annotated transcripts not associated with the "Viridiplantae" clade were taxonomically categorized. It was found that S. scabra quickly perceives and recovers from the oscillations of the imposed water regime. Physiologically, mechanisms that minimize evapotranspiration or protect the photosynthetic apparatus stood out. Biochemically, it was found that the root tissue invests in synthesizing compounds that can act as osmolytes (proline and sugars), emphasizing the importance of osmoregulation to water deficit acclimation. Consistently, transcriptome and qPCR analyses showed that a set of enriched biological processes with upregulated (UR) transcripts were involved in protective functions against reactive oxygen species or encoding enzymes of important metabolic pathways, which might contribute to S. scabra response to water deficit. Additionally, several UR kinases and transcription factors were identified. Finally, in an innovative approach, some naturally occurring microbial groups (such as Schizosaccharomyces, Bradyrhizobium, etc.) were identified in the S. scabra roots. This study reveals insights into the physiological, biochemical, and molecular mechanisms underlying the S. scabra response to water deficit and provides candidate genes that may be useful in developing drought-tolerant crop varieties through biotechnological applications.

MYB Transcription Factors Becoming Mainstream in Plant Roots

The function of the root system is crucial for plant survival, such as anchoring plants, absorbing nutrients and water from the soil, and adapting to stress. MYB transcription factors constitute one of the largest transcription factor families in plant genomes with structural and functional diversifications. Members of this superfamily in plant development and cell differentiation, specialized metabolism, and biotic and abiotic stress processes are widely recognized, but their roles in plant roots are still not well characterized. Recent advances in functional studies remind us that MYB genes may have potentially key roles in roots. In this review, the current knowledge about the functions of MYB genes in roots was summarized, including promoting cell differentiation, regulating cell division through cell cycle, response to biotic and abiotic stresses (e.g., drought, salt stress, nutrient stress, light, gravity, and fungi), and mediate phytohormone signals. MYB genes from the same subfamily tend to regulate similar biological processes in roots in redundant but precise ways. Given their increasing known functions and wide expression profiles in roots, MYB genes are proposed as key components of the gene regulatory networks associated with distinct biological processes in roots. Further functional studies of MYB genes will provide an important basis for root regulatory mechanisms, enabling a more inclusive green revolution and sustainable agriculture to face the constant changes in climate and environmental conditions.

Insights Into the MYB-Related Transcription Factors Involved in Regulating Floral Aroma Synthesis in Sweet Osmanthus

As an important member of the MYB transcription factor (TF) family, the MYB-related TFs play multiple roles in regulating the synthesis of secondary metabolites and developmental processes, as well as in response to numerous biotic and abiotic stressors in plants. However, little is known regarding their roles in regulating the formation of floral volatile organic compounds (VOCs). In this study, we conducted a genome-wide analysis of MYB-related proteins in sweet osmanthus; 212 OfMYB-related TFs were divided into three distinct subgroups based on the phylogenetic analysis. Additionally, we found that the expansion of the OfMYB-related genes occurred primarily through segmental duplication events, and purifying selection occurred in all duplicated gene pairs. RNA-seq data revealed that the OfMYB-related genes were widely expressed in different organs of sweet osmanthus, and some showed flower organ/development stage-preferential expression patterns. Here, three OfMYB-related genes (OfMYB1R70/114/201), which were expressed nuclearly in floral organs, were found to be significantly involved in regulating the synthesis of floral VOCs. Only, OfMYB1R201 had transcriptional activity, thus implying that this gene participates in regulating the expression of VOC synthesis related genes. Remarkably, the transient expression results suggested that OfMYB1R70, OfMYB1R114, and OfMYB1R201 are involved in the regulation of VOC synthesis; OfMYB1R114 and OfMYB1R70 are involved in accelerating β-ionone formation. In contrast, OfMYB1R201 decreases the synthesis of β-ionone. Our results deepen our knowledge of the functions of MYB-related TFs and provide critical candidate genes for the floral aroma breeding of sweet osmanthus in the future.

Shaping the root system architecture in plants for adaptation to drought stress

Root system architecture plays an important role in plant adaptation to drought stress. The root system architecture (RSA) consists of several structural features, which includes number and length of main and lateral roots along with the density and length of root hairs. These features exhibit plasticity under water-limited environments and could be critical to developing crops with efficient root systems for adaptation under drought. Recent advances in the omics approaches have significantly improved our understanding of the regulatory mechanisms of RSA remodeling under drought and the identification of genes and other regulatory elements. Plant response to drought stress at physiological, morphological, biochemical, and molecular levels in root cells is regulated by various phytohormones and their crosstalk. Stress-induced reactive oxygen species play a significant role in regulating root growth and development under drought stress. Several transcription factors responsible for the regulation of RSA under drought have proven to be beneficial for developing drought tolerant crops. Molecular breeding programs for developing drought-tolerant crops have been greatly benefitted by the availability of quantitative trait loci (QTLs) associated with the RSA regulation. In the present review, we have discussed the role of various QTLs, signaling components, transcription factors, microRNAs and crosstalk among various phytohormones in shaping RSA and present future research directions to better understand various factors involved in RSA remodeling for adaptation to drought stress. We believe that the information provided herein may be helpful in devising strategies to develop crops with better RSA for efficient uptake and utilization of water and nutrients under drought conditions.

PpNUDX8, a Peach NUDIX Hydrolase, Plays a Negative Regulator in Response to Drought Stress

Drought stress is a serious abiotic stress source that affects the growth and fruit quality of peach trees. However, the molecular mechanism of the NUDIX hydrolase family in peaches in response to drought stress is still unclear. Here, we isolated and identified the PpNUDX8 (Prupe.5G062300.1) gene from the peach NUDIX hydrolase family, and found that PpNUDX8 has a typical NUDIX hydrolase domain. In this study, we performed 15% PEG6000 drought treatment on peach seedlings, and qRT-PCR analysis showed that 15% PEG6000 induced the transcription level of PpNUDX8. Overexpression of PpNUDX8 reduced the tolerance of calli to 4% PEG6000 treatment. Compared with wild-type apple calli, PpNUDX8 transgenic apple calli had a lower fresh weight and higher MDA content. After 15% PEG6000 drought treatment, PpNUDX8 transgenic tobacco had a greater degree of wilting and shorter primary roots than Under control conditions. The chlorophyll, soluble protein, and proline contents in the transgenic tobacco decreased, and the MDA content and relative conductivity increased. At the same time, PpNUDX8 negatively regulated ABA signal transduction and reduced the transcriptional expression of stress response genes. In addition, PpNUDX8 was not sensitive to ABA, overexpression of PpNUDX8 reduced the expression of the ABA synthesis-related gene NCED6 and increases the expression of the ABA decomposition-related gene CYP1 in tobacco, which in turn leads to a decrease in the ABA content in tobacco. In addition, Under control conditions, overexpression of PpNUDX8 destroyed the homeostasis of NAD and reduced nicotinamide adenine dinucleotide (NADH) in tobacco. After 15% PEG6000 drought treatment, the changes in NAD and NADH in PpNUDX8 transgenic tobacco were more severe than those in WT tobacco. In addition, PpNUDX8 also interacted with PpSnRk1γ (Prupe.6G323700.1).

Genome-Wide Identification and Expression Analysis of the R2R3-MYB Transcription Factor Family Revealed Their Potential Roles in the Flowering Process in Longan (Dimocarpus longan)

Longan (Dimocarpus longan Lour.) is a productive fruit crop with high nutritional and medical value in tropical and subtropical regions. The MYB gene family is one of the most widespread plant transcription factor (TF) families participating in the flowering regulation. However, little is known about the MYB TFs involved in the flowering process in longan and its regulatory network. In this study, a total of 119 DlR2R3-MYB genes were identified in the longan genome and were phylogenetically grouped into 28 subgroups. The groupings were supported by highly conserved gene structures and motif composition of DlR2R3-MYB genes in each subgroup. Collinearity analysis demonstrated that segmental replications played a more crucial role in the expansion of the DlR2R3-MYB gene family compared to tandem duplications, and all tandem/segmental duplication gene pairs have evolved under purifying selection. Interspecies synteny analysis among longan and five representative species implied the occurrence of gene duplication events was one of the reasons contributing to functional differentiation among species. RNA-seq data from various tissues showed DlR2R3-MYB genes displayed tissue-preferential expression patterns. The pathway of flower development was enriched with six DlR2R3-MYB genes. Cis-acting element prediction revealed the putative functions of DlR2R3-MYB genes were related to the plant development, phytohormones, and environmental stresses. Notably, the orthologous counterparts between Arabidopsis and longan R2R3-MYB members tended to play conserved roles in the flowering regulation and stress responses. Transcriptome profiling on off-season flower induction (FI) by KClO₃ indicated two up-regulated and four down-regulated DlR2R3-MYB genes involved in the response to KClO₃ treatment compared with control groups. Additionally, qRT-PCR confirmed certain genes exhibited high expression in flowers/flower buds. Subcellular localization experiments revealed that three predicted flowering-associated MYB proteins were localized in the nucleus. Future functional studies on these potential candidate genes involved in the flowering development could further the understanding of the flowering regulation mechanism.

Global Transcriptomic Analysis Reveals Differentially Expressed Genes Involved in Embryogenic Callus Induction in Drumstick (Moringa oleifera Lam.)

The plant embryogenic callus (EC) is an irregular embryogenic cell mass with strong regenerative ability that can be used for propagation and genetic transformation. However, difficulties with EC induction have hindered the breeding of drumstick, a tree with diverse potential commercial uses. In this study, three drumstick EC cDNA libraries were sequenced using an Illumina NovaSeq 6000 system. A total of 7191 differentially expressed genes (DEGs) for embryogenic callus development were identified, of which 2325 were mapped to the KEGG database, with the categories of plant hormone signal transduction and Plant-pathogen interaction being well-represented. The results obtained suggest that auxin and cytokinin metabolism and several embryogenesis-labeled genes are involved in embryogenic callus induction. Additionally, 589 transcription factors from 20 different families were differentially expressed during EC formation. The differential expression of 16 unigenes related to auxin signaling pathways was validated experimentally by quantitative real time PCR (qRT-PCR) using samples representing three sequential developmental stages of drumstick EC, supporting their apparent involvement in drumstick EC formation. Our study provides valuable information about the molecular mechanism of EC formation and has revealed new genes involved in this process.

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.

NAC Transcription Factor PwNAC11 Activates ERD1 by Interaction with ABF3 and DREB2A to Enhance Drought Tolerance in Transgenic Arabidopsis

NAC (NAM, ATAF1/2, and CUC2) transcription factors are ubiquitously distributed in eukaryotes and play significant roles in stress response. However, the functional verifications of NACs in Picea (P.) wilsonii remain largely uncharacterized. Here, we identified the NAC transcription factor PwNAC11 as a mediator of drought stress, which was significantly upregulated in P. wilsonii under drought and abscisic acid (ABA) treatments. Yeast two-hybrid assays showed that both the full length and C-terminal of PwNAC11 had transcriptional activation activity and PwNAC11 protein cannot form a homodimer by itself. Subcellular observation demonstrated that PwNAC11 protein was located in nucleus. The overexpression of PwNAC11 in Arabidopsis obviously improved the tolerance to drought stress but delayed flowering time under nonstress conditions. The steady-state level of antioxidant enzymes' activities and light energy conversion efficiency were significantly increased in PwNAC11 transgenic lines under dehydration compared to wild plants. PwNAC11 transgenic lines showed hypersensitivity to ABA and PwNAC11 activated the expression of the downstream gene ERD1 by binding to ABA-responsive elements (ABREs) instead of drought-responsive elements (DREs). Genetic evidence demonstrated that PwNAC11 physically interacted with an ABA-induced protein-ABRE Binding Factor3 (ABF3)-and promoted the activation of ERD1 promoter, which implied an ABA-dependent signaling cascade controlled by PwNAC11. In addition, qRT-PCR and yeast assays showed that an ABA-independent gene-DREB2A-was also probably involved in PwNAC11-mediated drought stress response. Taken together, our results provide the evidence that PwNAC11 plays a dominant role in plants positively responding to early drought stress and ABF3 and DREB2A synergistically regulate the expression of ERD1.

Genome-Wide Analysis of Myeloblastosis-Related Genes in Brassica napus L. and Positive Modulation of Osmotic Tolerance by BnMRD107

Myeloblastosis (MYB)-related transcription factors comprise a large subfamily of the MYB family. They play significant roles in plant development and in stress responses. However, MYB-related proteins have not been comprehensively investigated in rapeseed (Brassica napus L.). In the present study, a genome-wide analysis of MYB-related transcription factors was performed in rapeseed. We identified 251 Brassica napus MYB (BnMYB)-related members, which were divided phylogenetically into five clades. Evolutionary analysis suggested that whole genome duplication and segmental duplication events have played a significant role in the expansion of BnMYB-related gene family. Selective pressure of BnMYB-related genes was estimated using the Ka/Ks ratio, which indicated that BnMYB-related genes underwent strong purifying selection during evolution. In silico analysis showed that various development-associated, phytohormone-responsive, and stress-related cis-acting regulatory elements were enriched in the promoter regions of BnMYB-related genes. Furthermore, MYB-related genes with tissue or organ-specific, stress-responsive expression patterns were identified in B. napus based on temporospatial and abiotic stress expression profiles. Among the stress-responsive MYB-related genes, BnMRD107 was strongly induced by drought stress, and was therefore selected for functional study. Rapeseed seedlings overexpressing BnMRD107 showed improved resistance to osmotic stress. Our findings not only lay a foundation for further functional characterization of BnMYB-related genes, but also provide valuable clues to determine candidate genes for future genetic improvement of B. napus.

Identification and characterization of 5 walnut MYB genes in response to drought stress involved in ABA signaling

Walnut is a popular nut tree species and usually suffers from drought stress. However, little information is available on the mechanism of walnut responding to drought stress, resulting in lack of basic understanding for its resistance. In order to excavate more functional genes that can respond to stressors, and enrich the theoretical basis for walnut resistance, in this study, 5 MYB genes with complete ORFs were identified from J. regia and the basic bio-information as well as expression patterns in different tissues and response to drought and ABA stresses were confirmed using qRT-PCR assay. The results showed that 2 JrMYB genes belong to R1-MYB subfamily and 3 JrMYBs belong to R2R3-MYB, encoding the proteins from 212 to 362 aa in length. The phylogenetic analysis categorized proteins of 5 JrMYBs and 40 Arabidopsis AtMYBs into 10 subgroups. JrMYBs in the same subgroup exhibited significant similarities in the composition of conserved domains and motifs in amino acid sequences and exon/intron organization in DNA sequences. The results of qRT-PCR analysis revealed that JrMYB genes diversely expressed in various tissues. Moreover, the expression values of JrMYBs were upregulated or downregulated significantly under drought and ABA stresses. Most attractively, in contrast with suffering from drought stress alone, the treatments with drought and additional ABA greatly enhanced the transcript levels of JrMYBs. All these results suggested that JrMYB genes play a vital role in plant biological processes and drought as well as ABA stress response, and possibly perform as ABA-dependent drought response transcription factors in plant.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01008-z.

Comprehensive Transcriptome Analysis of Rare Carpinus putoensis Plants under NO2 stress

We evaluated a transcriptome using high-throughput Illumina HiSeq sequencing and related it to the morphology, leaf anatomy, and physiological parameters of Carpinus putoensis putoensis under NO₂ stress. The molecular mechanism of the C. putoensis NO₂ stress response was evaluated using sequencing data. NO₂ stress adversely affected the morphology, leaf anatomy, and total peroxidase (POD) activity. Through RNA-seq analysis, we used NCBI to compare the transcripts with nine databases and obtained their functional annotations. We annotated up to 2255 million clean Illumina paired-end RNA-seq reads, and 250,200 unigene sequences were assembled based on the resulting transcriptome data. More than 89% of the C. putoensis transcripts were functionally annotated. Under NO₂ stress, 1119 genes were upregulated and 1240 were downregulated. According to the KEGG pathway and GO analyses, photosynthesis, chloroplasts, plastids, and the stimulus response are related to NO₂ stress. Additionally, NO₂ stress changed the expression of POD families, and the HPL2, HPL1, and POD genes exhibited high expression. The transcriptome analysis of C. putoensis leaves under NO₂ stress supplies a reference for studying the molecular mechanism of C. putoensis resistance to NO₂ stress. The given transcriptome data represent a valuable resource for studies on plant genes, which will contribute towards genome annotations during future genome projects.

Late embryogenesis abundant (LEA) gene family in Salvia miltiorrhiza: identification, expression analysis, and response to drought stress

Late embryogenesis abundant (LEA) proteins play important roles in plant defense response to drought stress. However, genome-wide identification of the LEA gene family was not revealed in Salvia miltiorrhiza. In this study, 61 SmLEA genes were identified from S. miltiorrhiza and divided into 7 subfamilies according to their conserved domains and phylogenetic relationships. SmLEA genes contained the LEA conserved motifs and few introns. SmLEA genes of the same subfamilies had similar gene structures and predicted subcellular locations. Our results indicated that the promoters of SmLEA genes contained various cis-acting elements associated with abiotic stress response. In addition, RNA-seq and real-time PCR results suggested that SmLEA genes are specifically expressed in different tissue, and most SmLEA genes can be induced by drought stress. These results provide a valuable foundation for future functional investigations of SmLEA genes and drought stress-resistant breeding of S. miltiorrhiza.

Isolation and characterization of maize ZmPP2C26 gene promoter in drought-response

The clade A members of serine/threonine protein phosphatase 2Cs (PP2Cs) play crucial roles in plant growth, development, and stress response via the ABA signaling pathway. But little is known about other PP2C clades in plants. Our previous study showed that maize the ZmPP2C26, a clade B member of ZmPP2Cs, negatively regulated drought tolerance in transgenic Arabidopsis. However, the upstream regulatory mechanism of ZmPP2C26 remains unclear. In the present study, the expression of ZmPP2C26 gene in maize was analyzed by quantitative real time PCR (qRT-PCR). The results showed that the expression of ZmPP2C26 in shoot and root was both significantly inhibited by drought stress. Subsequently, a 2175 bp promoter of ZmPP2C26 was isolated from maize genome (P ₂₁₇₅). To validate whether the promoter possess some key cis-element and negatively drive ZmPP2C26 expression in drought stress, three 5´-deletion fragments of 1505, 1084 and 215 bp was amplified from P ₂₁₇₅ and were fused to β-glucuronidase (GUS) and luciferase gene (LUC) to produce promoter::GUS and promoter::LUC constructs, and transformed into tobacco, respectively. Transient expression assays indicated that all promoters could drive GUS and LUC expression. The GUS and LUC activity were both significantly inhibited by PEG-6000 treatment. Notably, the - 1084 to - 215 bp promoter possess one MBS element and inhibits the expression of GUS and LUC under drought stress. Meanwhile, we found that the 215 bp length is enough to drive ZmPP2C26 expression. These findings will provide insights into understanding the transcription-regulatory mechanism of ZmPP2C26 negatively regulating drought tolerance.

Overexpression of Maize ZmMYB59 Gene Plays a Negative Regulatory Role in Seed Germination in Nicotiana tabacum and Oryza sativa

MYB transcription factors are involved in many biological processes, including metabolism, stress response and plant development. In our previous work, ZmMYB59 was down-regulated by deep sowing during maize seed germination. However, there are few reports on seed germination regulated by MYB proteins. In this study, to examine its functions during seed germination, Agrobacterium-mediated transformation was exploited to generate ZmMYB59 overexpression (OE) tobacco and rice. In T2 generation transgenic tobacco, germination rate, germination index, vigor index and hypocotyl length were significantly decreased by 25.0-50.9, 34.5-54.4, 57.5-88.3, and 21.9-31.3% compared to wild-type (WT) lines. In T2 generation transgenic rice, above corresponding parameters were notably reduced by 39.1-53.8, 51.4-71.4, 52.5-74.0, and 28.3-41.5%, respectively. On this basis, antioxidant capacity and endogenous hormones were determined. The activities of catalase, peroxidase, superoxide dismutase, ascorbate peroxidase of OE lines were significantly lower than those of WT, suggesting that ZmMYB59 reduced their oxidation resistance. As well, ZmMYB59 overexpression extremely inhibited the synthesis of gibberellin A1 (GA1) and cytokinin (CTK), and promoted the synthesis of abscisic acid (ABA) concurrently. Taken together, it proposed that ZmMYB59 was a negative regulator during seed germination in tobacco and rice, which also contributes to illuminate the molecular mechanisms regulated by MYB transcription factors.

A Leymus chinensis histidine-rich Ca2+-binding protein binds Ca2+/Zn2+ and suppresses abscisic acid signaling in Arabidopsis

Intracellular Ca²⁺ plays an essential role in plant cellular sensing of various environmental stress signals by modulating the activity of Ca²⁺-binding proteins. Leymus chinensis is a dominant forage grass widely distributed in the Eurasian Steppe that is well adapted to drought and salty soils common in the region. Through transcript profiling of L. chinensis roots, we identified a transcript predicted to encode histidine-rich calcium-binding protein (HRC), a protein recently characterized in wheat. L. chinensis HRC (LcH RC) localized in the nucleus, as demonstrated using a transient gene expression method that we developed for this species. Different regions of LcHRC showed affinity for either Ca²⁺ or Zn²⁺, but not Mg²⁺ and Mn²⁺. Arabidopsis thaliana seedlings heterologously overexpressing LcHRC showed greater sensitivity to abscisic acid (ABA), along with decreased expression of some ABA-induced marker genes, but no increase in ABA content. Screening a Arabidopsis cDNA yeast library identified a Tudor/PWWP/MBT-domain-containing protein (AtPWWP3) that interacts with LcHRC. AtPWWP3 also localized in the nucleus and is predicted to mediate gene expression by modifying histone deacetylation. Based on these results, we propose a functional model of LcHRC action.