WRKY transcription factors in legumes

WRKY transcription factors modulate flowering time in four Arachis species: a bioinformatics analysis

BACKGROUND

WRKY proteins are important transcription factors (TFs) in plants, involved in growth and development and responses to environmental changes. Although WRKY TFs have been studied at the genome level in Arachis genus, including oil crop and turfgrass, their regulatory networks in controlling flowering time remain unclear. The aim of this study was to predict the molecular mechanisms of WRKY TFs regulation flowering time in Arachis genus at the genome level using bioinformatics approaches.

RESULTS

The flowering-time genes of Arachis genus were retrieved from the flowering-time gene database. The regulatory networks between WRKY TFs and downstream genes in Arachis genus were predicted using bioinformatics tools. The results showed that WRKY TFs were involved in aging, autonomous, circadian clock, hormone, photoperiod, sugar, temperature, and vernalization pathways to modulate flowering time in Arachis duranensis, Arachis ipaensis, Arachis monticola, and Arachis hypogaea cv. Tifrunner. The WRKY TF binding sites in homologous flowering-time genes exhibited asymmetric evolutionary pattern, indicating that the WRKY TFs interact with other transcription factors to modulate flowering time in the four Arachis species. Protein interaction network analysis showed that WRKY TFs interacted with FRUITFULL and APETALA2 to modulate flowering time in the four Arachis species. WRKY TFs implicated in regulating flowering time had low expression levels, whereas their interaction proteins had varying expression patterns in 22 tissues of A. hypogaea cv. Tifrunner. These results indicate that WRKY TFs exhibit antagonistic or synergistic interactions with the associated proteins.

CONCLUSIONS

This study reveals complex regulatory networks through which WRKY TFs modulate flowering time in the four Arachis species using bioinformatics approaches.

In Silico Comparison of WRKY Transcription Factors in Wild and Cultivated Soybean and Their Co-expression Network Arbitrating Disease Resistance

WRKY Transcription factors (TFs) play critical roles in plant defence mechanisms that are activated in response to biotic and abiotic stresses. However, information on the Glycine soja WRKYs (GsoWRKYs) is scarce. Owing to its importance in soybean breeding, here we identified putative WRKY TFs in wild soybean, and compared the results with Glycine max WRKYs (GmaWRKYs) by phylogenetic, conserved motif, and duplication analyses. Moreover, we explored the expression trends of WRKYs in G. max (oomycete, fungi, virus, bacteria, and soybean cyst nematode) and G. soja (soybean cyst nematode), and identified commonly expressed WRKYs and their co-expressed genes. We identified, 181 and 180 putative WRKYs in G. max and G. soja, respectively. Though the number of WRKYs in both studied species is almost the same, they differ in many ways, i.e., the number of WRKYs on corresponding chromosomes, conserved domain structures, WRKYGQK motif variants, and zinc-finger motifs. WRKYs in both species grouped in three major clads, i.e., I-III, where group-II had sub-clads IIa-IIe. We found that GsoWRKYs expanded mostly through segmental duplication. A large number of WRKYs were expressed in response to biotic stresses, i.e., Phakospora pachyrhizi, Phytoplasma, Heterodera glycines, Macrophomina phaseolina, and Soybean mosaic virus; 56 GmaWRKYs were commonly expressed in soybean plants infected with these diseases. Finally, 30 and 63 GmaWRKYs and GsoWRKYs co-expressed with 205 and 123 non-WRKY genes, respectively, indicating that WRKYs play essential roles in biotic stress tolerance in Glycine species.

Transcriptome and Metabolome Analysis of Isoquinoline Alkaloid Biosynthesis of Coptis chinensis in Different Years

Coptis chinensis is a perennial herb of the Ranunculaceae family. The isoquinoline alkaloid is the main active component of C. chinensis, mainly exists in its rhizomes and has high clinical application potential. The in vitro synthesis of isoquinoline alkaloids is difficult because their structures are complex; hence, plants are still the main source of them. In this study, two-year and four-year rhizomes of C. chinensis were selected to investigate the effect of growth years on the accumulation of isoquinoline alkaloids. Two-year and four-year C. chinensis were selected for metabolomics detection and transcriptomic analysis. A total of 413 alkaloids were detected by metabolomics analysis, of which 92 were isoquinoline alkaloids. (S)-reticuline was a significantly different accumulated metabolite of the isoquinoline alkaloids biosynthetic pathway in C. chinensis between the two groups. The results of transcriptome analysis showed that a total of 464 differential genes were identified, 36 of which were associated with the isoquinoline alkaloid biosynthesis pathway of C. chinensis. Among them, 18 genes were correlated with the content of important isoquinoline alkaloids. Overall, this study provided a comprehensive metabolomic and transcriptomic analysis of the rapid growth stage of C. chinensis rhizome from the perspective of growth years. It brought new insights into the biosynthetic pathway of isoquinoline alkaloids and provided information for utilizing biotechnology to improve their contents in C. chinensis.

Multifaceted roles of WRKY transcription factors in abiotic stress and flavonoid biosynthesis

Increasing biotic and abiotic stresses are seriously impeding the growth and yield of staple crops and threatening global food security. As one of the largest classes of regulators in vascular plants, WRKY transcription factors play critical roles governing flavonoid biosynthesis during stress responses. By binding major W-box cis-elements (TGACCA/T) in target promoters, WRKYs modulate diverse signaling pathways. In this review, we optimized existing WRKY phylogenetic trees by incorporating additional plant species with WRKY proteins implicated in stress tolerance and flavonoid regulation. Based on the improved frameworks and documented results, we aim to deduce unifying themes of distinct WRKY subfamilies governing specific stress responses and flavonoid metabolism. These analyses will generate experimentally testable hypotheses regarding the putative functions of uncharacterized WRKY homologs in tuning flavonoid accumulation to enhance stress resilience.

WRKY transcription factors in Arachis hypogaea and its donors: From identification to function prediction

WRKY transcription factors (TFs) play important roles in plant growth and development and responses to abiotic and biotic stresses. Since the initial isolation of a WRKY TF in Ipomoea batatas in 1994, WRKY TFs have been identified in plants, protozoa, and fungi. Peanut (Arachis hypogaea) is a key oil and protein crop for humans and a forage source for animal consumption. Several Arachis genomes have been sequenced and genome-wide WRKY TFs have been identified. In this review, we summarized WRKY TFs and their functions in A. hypogaea and its donors. We also standardized the nomenclature for Arachis WRKY TFs to ensure uniformity. We determined the evolutionary relationships between Arachis and Arabidopsis thaliana WRKY (AtWRKY) TFs using a phylogenetic analysis. Biological functions and regulatory networks of Arachis WRKY TFs were predicted using AtWRKY TFs. Thus, this review paves the way for studies of Arachis WRKY TFs.

New potential roles of StDREB1 and VvWRKY2 transcription factors in potato dormancy and sprouting patterns

In a previous study, transgenic potato plants overexpressing the StDREB1 or the VvWRKY2 transcription factor (TF) proved to have higher productivity and ameliorated tuber quality in comparison to wildtype (WT; the BF15 variety) plants. Interestingly, when stored at 4 °C, we noticed that the tubers of transgenic potato plants exhibited a delay in sprouting, hence a longer dormancy period. Therefore, we decided to study the dormancy and sprouting of these tubers (the two transgenic and the WT lines) through a physiological and biochemical characterization. WT and genetically modified (GM) tubers were stored at 4 °C for different periods (0, 30, 90, 180, and 240 days) followed by placing them in a germination chamber and the sprouting parameters were then monitored. According to our findings, the overexpression of these two TFs led to modifications in the sprouting kinetic of tubers through an extension of the dormancy period and changes in the sprouting process. Indeed, WT tubers emitted apical and lateral sprouts while those from GM plants showed mainly apical sprouts. In addition, higher reactive oxygen species (ROS) rates, indicators of tuber aging, were recorded in WT tubers compared to GM ones. The higher antioxidant enzyme activities in GM tubers seem to be responsible for aging modification in comparison to WT. The above results suggest the first report on new roles of the StDREB1 and VvWRKY2 TF which seemed to be involved in the regulation of potato tuber aging via a reduction of the main biochemical factors concentration and the ROS content leading to a longer dormancy period and a modified sprouting pattern.

OsWRKY97, an Abiotic Stress-Induced Gene of Rice, Plays a Key Role in Drought Tolerance

Drought stress is one of the major causes of crop losses. The WRKY families play important roles in the regulation of many plant processes, including drought stress response. However, the function of individual WRKY genes in plants is still under investigation. Here, we identified a new member of the WRKY families, OsWRKY97, and analyzed its role in stress resistance by using a series of transgenic plant lines. OsWRKY97 positively regulates drought tolerance in rice. OsWRKY97 was expressed in all examined tissues and could be induced by various abiotic stresses and abscisic acid (ABA). OsWRKY97-GFP was localized to the nucleus. Various abiotic stress-related cis-acting elements were observed in the promoters of OsWRKY97. The results of OsWRKY97-overexpressing plant analyses revealed that OsWRKY97 plays a positive role in drought stress tolerance. In addition, physiological analyses revealed that OsWRKY97 improves drought stress tolerance by improving the osmotic adjustment ability, oxidative stress tolerance, and water retention capacity of the plant. Furthermore, OsWRKY97-overexpressing plants also showed higher sensitivity to exogenous ABA compared with that of wild-type rice (WT). Overexpression of OsWRKY97 also affected the transcript levels of ABA-responsive genes and the accumulation of ABA. These results indicate that OsWRKY97 plays a crucial role in the response to drought stress and may possess high potential value in improving drought tolerance in rice.

Review: WRKY transcription factors: Understanding the functional divergence

WRKY transcription factors (TFs) play crucial roles in the growth and development of plants and their response to environmental changes. WRKY TFs have been detected in sequenced plant genomes. The functions and regulatory networks of many WRKY TFs, especially from Arabidopsis thaliana (AtWRKY TFs), have been revealed, and the origin of WRKY TFs in plants is clear. Nonetheless, the relationship between WRKY TFs function and classification is unclear. Furthermore, the functional divergence of homologous WRKY TFs in plants is unclear. In this review, WRKY TFs were explored based on WRKY-related literature published from 1994 to 2022. WRKY TFs were identified in 234 species at the genome and transcriptome levels. The biological functions of ∼ 71 % of AtWRKY TFs were uncovered. Although functional divergence occurred in homologous WRKY TFs, different WRKY TF groups had no preferential function.

Cell Mutagenic Autopolyploidy Enhances Salinity Stress Tolerance in Leguminous Crops

Salinity stress affects plant growth and development by causing osmotic stress and nutrient imbalances through excess Na+, K+, and Cl- ion accumulations that induce toxic effects during germination, seedling development, vegetative growth, flowering, and fruit set. However, the effects of salt stress on growth and development processes, especially in polyploidized leguminous plants, remain unexplored and scantly reported compared to their diploid counterparts. This paper discusses the physiological and molecular response of legumes towards salinity stress-based osmotic and ionic imbalances in plant cells. A multigenic response involving various compatible solutes, osmolytes, ROS, polyamines, and antioxidant activity, together with genes encoding proteins involved in the signal transduction, regulation, and response mechanisms to this stress, were identified and discussed. This discussion reaffirms polyploidization as the driving force in plant evolution and adaptation to environmental stress constraints such as drought, feverish temperatures, and, in particular, salt stress. As a result, thorough physiological and molecular elucidation of the role of gene duplication through induced autopolyploidization and possible mechanisms regulating salinity stress tolerance in grain legumes must be further studied.

Genome-Wide Analysis of WRKY Transcription Factors Involved in Abiotic Stress and ABA Response in Caragana korshinskii

The WRKY transcription factor family plays a vital role in plant development and environmental response. However, the information of WRKY genes at the genome-wide level is rarely reported in Caragana korshinskii. In this study, we identified and renamed 86 CkWRKY genes, which were further classified into three groups through phylogenetic analysis. Most of these WRKY genes were clustered and distributed on eight chromosomes. Multiple sequence alignment revealed that the conserved domain (WRKYGQK) of the CkWRKYs was basically consistent, but there were also six variation types (WRKYGKK, GRKYGQK, WRMYGQK, WRKYGHK, WKKYEEK and RRKYGQK) that appeared. The motif composition of the CkWRKYs was quite conservative in each group. In general, the number of WRKY genes gradually increased from lower to higher plant species in the evolutionary analysis of 28 species, with some exceptions. Transcriptomics data and RT-qPCR analysis showed that the CkWRKYs in different groups were involved in abiotic stresses and ABA response. Our results provided a basis for the functional characterization of the CkWRKYs involved in stress resistance in C. korshinskii.

Seedling nanopriming with selenium-chitosan nanoparticles mitigates the adverse effects of salt stress by inducing multiple defence pathways in bitter melon plants

Advances in the nanotechnology fields provided crucial applications in plant sciences, contributing to the plant performance and health under stress and stress-free conditions. Amid the applications, selenium (Se), chitosan and their conjugated forms as nanoparticles (Se-CS NPs) have been revealed to have potential of alleviating the harmful effects of the stress on several crops and subsequently enhancing the growth and productivity. The present study was addressed to assay the potential effects of Se-CS NPs in reversing or buffering the harmful effects of salt stress on growth, photosynthesis, nutrient concentration, antioxidant system and defence transcript levels in bitter melon )Momordica charantia(. In addition, some secondary metabolite-related genes were explicitly examined. In this regard, the transcriptional levels of WRKY1, SOS1, PM H⁺-ATPase, SKOR, Mc5PTase7, SOAR1, MAP30, α-MMC, polypeptide-P and PAL were quantified. Our results demonstrated that Se-CS NPs increased growth parameters, photosynthesis parameters (SPAD, ^Fv/_Fm, Y(II)), antioxidant enzymatic activity (POD, SOD, CAT) and nutrient homeostasis (Na⁺/K⁺, Ca²⁺, and Cl^-) and induced the expression of genes in bitter melon plants under salt stress (p ≤ 0.05). Therefore, applying Se-CS NPs might be a simple and effective way of improving crop plants' overall health and yield under salt stress conditions.

Expansion and adaptive evolution of the WRKY transcription factor family in Avicennia mangrove trees

Mangroves are adapted to intertidal zones, which present extreme environmental conditions. WRKYs are among the most prominent transcription factors (TFs) in higher plants and act through various interconnected networks to regulate responses to multiple abiotic stressors. Here, based on omic data, we investigated the landscape and evolutionary patterns of WRKYs in the main mangrove genus Avicennia. We found that both the number and the proportion of TFs and WRKYs in Avicennia species exceeded their inland relatives, indicating a significant expansion of WRKYs in Avicennia. We identified 109 WRKY genes in the representative species Avicennia marina. Comparative genomic analysis showed that two recent whole-genome duplication (WGD) events played a critical role in the expansion of WRKYs, and 88% of Avicennia marina WRKYs (AmWRKYs) have been retained following these WGDs. Applying comparative transcriptomics on roots under experimental salt gradients, we inferred that there is high divergence in the expression of WGD-retained AmWRKYs. Moreover, we found that the expression of 16 AmWRKYs was stable between freshwater and moderately saline water but increased when the trees were exposed to high salinity. In particular, 14 duplicates were retained following the two recent WGD events, indicating potential neo- and sub-functionalization. We also found that WRKYs could interact with other upregulated genes involved in signalling pathways and natural antioxidant biosynthesis to enhance salt tolerance, contributing to the adaptation to intertidal zones. Our omic data of the WRKY family in A. marina broadens the understanding of how a TF family relates to the adaptive evolution of mangroves.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-023-00177-y.

Genome-wide investigation of the WRKY transcription factor gene family in weeping forsythia: expression profile and cold and drought stress responses

Weeping forsythia is a wide-spread shrub in China with important ornamental, medicinal and ecological values. It is widely distributed in China's warm temperate zone. In plants, WRKY transcription factors play important regulatory roles in seed germination, flower development, fruit ripening and coloring, and biotic and abiotic stress response. To date, WRKY transcription factors have not been systematically studied in weeping forsythia. In this study, we identified 79 WRKY genes in weeping forsythia and classified them according to their naming rules in Arabidopsis thaliana. Phylogenetic tree analysis showed that, except for IIe subfamily, whose clustering was inconsistent with A. thaliana clustering, other subfamily clustering groups were consistent. Cis-element analysis showed that WRKY genes related to pathogen resistance in weeping forsythia might be related to methyl jasmonate and salicylic acid-mediated signaling pathways. Combining cis-element and expression pattern analyses of WRKY genes showed that more than half of WRKY genes were involved in light-dependent development and morphogenesis in different tissues. The gene expression results showed that 13 WRKY genes were involved in drought response, most of which might be related to the abscisic acid signaling pathway, and a few of which might be regulated by MYB transcription factors. The gene expression results under cold stress showed that 17 WRKY genes were involved in low temperature response, and 9 of them had low temperature responsiveness cis-elements. Our study of WRKY family in weeping forsythia provided useful resources for molecular breeding and important clues for their functional verification.

WRKY transcription factors: evolution, regulation, and functional diversity in plants

The recent advancements in sequencing technologies and informatic tools promoted a paradigm shift to decipher the hidden biological mysteries and transformed the biological issues into digital data to express both qualitative and quantitative forms. The transcriptomic approach, in particular, has added new dimensions to the versatile essence of plant genomics through the large and deep transcripts generated in the process. This has enabled the mining of super families from the sequenced plants, both model and non-model, understanding their ancestry, diversity, and evolution. The elucidation of the crystal structure of the WRKY proteins and recent advancement in computational prediction through homology modeling and molecular dynamic simulation has provided an insight into the DNA-protein complex formation, stability, and interaction, thereby giving a new dimension in understanding the WRKY regulation. The present review summarizes the functional aspects of the high volume of sequence data of WRKY transcription factors studied from different species, till date. The review focuses on the dynamics of structural classification and lineage in light of the recent information. Additionally, a comparative analysis approach was incorporated to understand the functions of the identified WRKY transcription factors subjected to abiotic (heat, cold, salinity, senescence, dark, wounding, UV, and carbon starvation) stresses as revealed through various sets of studies on different plant species. The review will be instrumental in understanding the events of evolution and the importance of WRKY TFs under the threat of climate change, considering the new scientific evidences to propose a fresh perspective.

Overexpression of CmWRKY8-1-VP64 Fusion Protein Reduces Resistance in Response to Fusarium oxysporum by Modulating the Salicylic Acid Signaling Pathway in Chrysanthemum morifolium

Chrysanthemum Fusarium wilt, caused by the pathogenic fungus Fusarium oxysporum, severely reduces ornamental quality and yields. WRKY transcription factors are extensively involved in regulating disease resistance pathways in a variety of plants; however, it is unclear how members of this family regulate the defense against Fusarium wilt in chrysanthemums. In this study, we characterized the WRKY family gene CmWRKY8-1 from the chrysanthemum cultivar 'Jinba', which is localized to the nucleus and has no transcriptional activity. We obtained CmWRKY8-1 transgenic chrysanthemum lines overexpressing the CmWRKY8-1-VP64 fusion protein that showed less resistance to F. oxysporum. Compared to Wild Type (WT) lines, CmWRKY8-1 transgenic lines had lower endogenous salicylic acid (SA) content and expressed levels of SA-related genes. RNA-Seq analysis of the WT and CmWRKY8-1-VP64 transgenic lines revealed some differentially expressed genes (DEGs) involved in the SA signaling pathway, such as PAL, AIM1, NPR1, and EDS1. Based on Gene Ontology (GO) enrichment analysis, the SA-associated pathways were enriched. Our results showed that CmWRKY8-1-VP64 transgenic lines reduced the resistance to F. oxysporum by regulating the expression of genes related to the SA signaling pathway. This study demonstrated the role of CmWRKY8-1 in response to F. oxysporum, which provides a basis for revealing the molecular regulatory mechanism of the WRKY response to F. oxysporum infestation in chrysanthemum.

Deciphering evolutionary dynamics of WRKY genes in Arachis species

BACKGROUND

Cultivated peanut (Arachis hypogaea), a progeny of the cross between A. duranensis and A. ipaensis, is an important oil and protein crop from South America. To date, at least six Arachis genomes have been sequenced. WRKY transcription factors (TFs) play crucial roles in plant growth, development, and response to abiotic and biotic stresses. WRKY TFs have been identified in A. duranensis, A. ipaensis, and A. hypogaea cv. Tifrunner; however, variations in their number and evolutionary patterns across various Arachis spp. remain unclear.

RESULTS

WRKY TFs were identified and compared across different Arachis species, including A. duranensis, A. ipaensis, A. monticola, A. hypogaea cultivars (cv.) Fuhuasheng, A. hypogaea cv. Shitouqi, and A. hypogaea cv. Tifrunner. The results showed that the WRKY TFs underwent dynamic equilibrium between diploid and tetraploid peanut species, characterized by the loss of old WRKY TFs and retention of the new ones. Notably, cultivated peanuts inherited more conserved WRKY orthologs from wild tetraploid peanuts than their wild diploid donors. Analysis of the W-box elements and protein-protein interactions revealed that different domestication processes affected WRKY evolution across cultivated peanut varieties. WRKY TFs of A. hypogaea cv. Fuhuasheng and Shitouqi exhibited a similar domestication process, while those of cv. Tifrunner of the same species underwent a different domestication process based on protein-protein interaction analysis.

CONCLUSIONS

This study provides new insights into the evolution of WRKY TFs in Arachis spp.

Comprehensive Genomic Survey, Structural Classification, and Expression Analysis of WRKY Transcription Factor Family in Rhododendron simsii

(1) Rhododendron is one of the top ten traditional flowers in China, with both high ornamental and economic values. However, with the change of the environment, Rhododendron suffers from various biological stresses. The WRKY transcription factor is a member of the most crucial transcription factor families, which plays an essential regulatory role in a variety of physiological processes and developmental stresses. (2) In this study, 57 RsWRKYs were identified using genome data and found to be randomly distributed on 13 chromosomes. Based on gene structure and phylogenetic relationships, 57 proteins were divided into three groups: I, II, and III. Multiple alignments of RsWRKYs with Arabidopsis thaliana homologous genes revealed that WRKY domains in different groups had different conserved sites. RsWRKYs have a highly conserved domain, WRKYGQK, with three variants, WRKYGKK, WRKYGEK, and WRKYGRK. Furthermore, cis-acting elements analysis revealed that all of the RsWRKYs had stress and plant hormone cis-elements, with figures varying by group. Finally, the expression patterns of nine WRKY genes treated with gibberellin acid (GA), methyl jasmonate (MeJA), heat, and drought in Rhododendron were also measured using quantitative real-time PCR (qRT-PCR). The results showed that the expression levels of the majority of RsWRKY genes changed in response to multiple phytohormones and abiotic stressors. (3) This current study establishes a theoretical basis for future studies on the response of RsWRKY transcription factors to various hormone and abiotic stresses as well as a significant foundation for the breeding of new stress-tolerant Rhododendron varieties.

Identification of the WRKY Gene Family and Characterization of Stress-Responsive Genes in Taraxacum kok-saghyz Rodin

WRKY transcription factors present unusual research value because of their critical roles in plant physiological processes and stress responses. Taraxacum kok-saghyz Rodin (TKS) is a perennial herb of dandelion in the Asteraceae family. However, the research on TKS WRKY TFs is limited. In this study, 72 TKS WRKY TFs were identified and named. Further comparison of the core motifs and the structure of the WRKY motif was analyzed. These TFs were divided into three groups through phylogenetic analysis. Genes in the same group of TkWRKY usually exhibit a similar exon-intron structure and motif composition. In addition, virtually all the TKS WRKY genes contained several cis-elements related to stress response. Expression profiling of the TkWRKY genes was assessed using transcriptome data sets and Real-Time RT-PCR data in tissues during physiological development, under abiotic stress and hormonal treatments. For instance, the TkWRKY18, TkWRKY23, and TkWRKY38 genes were significantly upregulated during cold stress, whereas the TkWRKY21 gene was upregulated under heat-stress conditions. These results could provide a basis for further studies on the function of the TKS WRKY gene family and genetic amelioration of TKS germplasm.

GmWRKY21, a Soybean WRKY Transcription Factor Gene, Enhances the Tolerance to Aluminum Stress in Arabidopsis thaliana

The WRKY transcription factors (TFs) are one of the largest families of TFs in plants and play multiple roles in plant growth and development and stress response. In this study, GmWRKY21 encoding a WRKY transcription factor was functionally characterized in Arabidopsis and soybean. The GmWRKY21 protein containing a highly conserved WRKY domain and a C₂H₂ zinc-finger structure is located in the nucleus and has the characteristics of transcriptional activation ability. The GmWRKY21 gene presented a constitutive expression pattern rich in the roots, leaves, and flowers of soybean with over 6-fold of relative expression levels and could be substantially induced by aluminum stress. As compared to the control, overexpression of GmWRKY21 in Arabidopsis increased the root growth of seedlings in transgenic lines under the AlCl₃ concentrations of 25, 50, and 100 μM with higher proline and lower MDA accumulation. The results of quantitative real-time polymerase chain reaction (qRT-PCR) showed that the marker genes relative to aluminum stress including ALMT, ALS3, MATE, and STOP1 were induced in GmWRKY21 transgenic plants under AlCl₃ treatment. The stress-related genes, such as KIN1, COR15A, COR15B, COR47, GLOS3, and RD29A, were also upregulated in GmWRKY21 transgenic Arabidopsis under aluminum stress. Similarly, stress-related genes, such as GmCOR47, GmDREB2A, GmMYB84, GmKIN1, GmGST1, and GmLEA, were upregulated in hair roots of GmWRKY21 transgenic plants. In summary, these results suggested that the GmWRKY21 transcription factor may promote the tolerance to aluminum stress mediated by the pathways regulating the expression of the acidic aluminum stress-responsive genes and abiotic stress-responsive genes.

GWAS and bulked segregant analysis reveal the Loci controlling growth habit-related traits in cultivated Peanut (Arachis hypogaea L.)

Background

Peanut (Arachis hypogaea L.) is a grain legume crop that originated from South America and is now grown around the world. Peanut growth habit affects the variety’s adaptability, planting patterns, mechanized harvesting, disease resistance, and yield. The objective of this study was to map the quantitative trait locus (QTL) associated with peanut growth habit-related traits by combining the genome-wide association analysis (GWAS) and bulked segregant analysis sequencing (BSA-seq) methods.

Results

GWAS was performed with 17,223 single nucleotide polymorphisms (SNPs) in 103 accessions of the U.S. mini core collection genotyped using an Affymetrix version 2.0 SNP array. With a total of 12,342 high-quality polymorphic SNPs, the 90 suggestive and significant SNPs associated with lateral branch angle (LBA), main stem height (MSH), lateral branch height (LBL), extent radius (ER), and the index of plant type (IOPT) were identified. These SNPs were distributed among 15 chromosomes. A total of 597 associated candidate genes may have important roles in biological processes, hormone signaling, growth, and development. BSA-seq coupled with specific length amplified fragment sequencing (SLAF-seq) method was used to find the association with LBA, an important trait of the peanut growth habit. A 4.08 Mb genomic region on B05 was associated with LBA. Based on the linkage disequilibrium (LD) decay distance, we narrowed down and confirmed the region within the 160 kb region (144,193,467–144,513,467) on B05. Four candidate genes in this region were involved in plant growth. The expression levels of Araip.E64SW detected by qRT-PCR showed significant difference between ‘Jihua 5’ and ‘M130’.

Conclusions

In this study, the SNP (AX-147,251,085 and AX-144,353,467) associated with LBA by GWAS was overlapped with the results in BSA-seq through combined analysis of GWAS and BSA-seq. Based on LD decay distance, the genome range related to LBA on B05 was shortened to 144,193,467–144,513,467. Three candidate genes related to F-box family proteins (Araip.E64SW, Araip.YG1LK, and Araip.JJ6RA) and one candidate gene related to PPP family proteins (Araip.YU281) may be involved in plant growth and development in this genome region. The expression analysis revealed that Araip.E64SW was involved in peanut growth habits. These candidate genes will provide molecular targets in marker-assisted selection for peanut growth habits.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08640-3.

The WRKY transcription factor family in cowpea: Genomic characterization and transcriptomic profiling under root dehydration

Cowpea [Vigna unguiculata (L.) Walp.] is one of the most tolerant legume crops to drought and salt stresses. WRKY transcription factor (TF) family members stand out among plant transcriptional regulators related to abiotic stress tolerance. However, little information is currently available on the expression of the cowpea WRKY gene family (VuWRKY) in response to water deficit. Thus, we analyzed genomic and transcriptomic data from cowpea to identify VuWRKY members and characterize their structure and transcriptional response under root dehydration stress. Ninety-two complete VuWRKY genes were found in the cowpea genome based on their domain characteristics. They were clustered into three groups: I (15 members), II (58), and III (16), while three genes were unclassified. Domain analysis of the encoded proteins identified four major variants of the conserved heptapeptide motif WRKYGQK. In silico analysis of VuWRKY gene promoters identified eight candidate binding motifs of cis-regulatory elements, regulated mainly by six TF families associated with abiotic stress responses. Ninety-seven VuWRKY modulated splicing variants associated with 55 VuWRKY genes were identified via RNA-Seq analysis available at the Cowpea Genomics Consortium (CpGC) database. qPCR analyses showed that 22 genes are induced under root dehydration, with VuWRKY18, 21, and 75 exhibiting the most significant induction levels. Given their central role in activating signal transduction cascades in abiotic stress response, the data provide a foundation for the targeted modification of specific VuWRKY family members to improve drought tolerance in this important climate-resilient legume in the developing world and beyond.

Genome-Wide Analysis and Exploration of WRKY Transcription Factor Family Involved in the Regulation of Shoot Branching in Petunia

The WRKY transcription factors (TFs) participate in various physiological, growth and developmental processes of plants. In our study, a total of 79 WRKY family members were identified and classified into three groups (Group I, Group IIa-e, and Group III) based on phylogenetic and conservative domain analyses. Conserved motif analysis showed that seven WRKYGQK domains changed. The promoter sequence analysis suggested that there were multiple stress- and hormone-related cis-regulatory elements in the promoter regions of PhWRKY genes. Expression patterns of PhWRKYs based on RNA-seq data revealed their diverse expression profiles in five tissues and under different treatments. Subcellular localization analysis showed that PhWRKY71 was located in the nucleus. In addition, overexpression of PhWRKY71 caused a significant increase in branch number. This indicated that PhWRKY71 played a critical role in regulating the shoot branching of Petuniahybrida. The above results lay the foundation for further revealing the functions of PhWRKY genes.

Dissection of valine-glutamine genes and their responses to drought stress in Arachis hypogaea cv. Tifrunner

Valine-glutamine sequences (VQs) interact with WRKY transcription factors (TFs), forming VQ-WRKY protein complexes crucial for plant development and response to environmental changes. Cultivated peanut (Arachis hypogaea) is a tetraploid from A. duranensis and A. ipaensis cross. The Arachis spp. WRKY TFs have been identified, but Arachis VQs are largely unknown. This study identified VQs in A. duranensis, A. ipaensis, A. monticola, A. hypogaea cv. Fuhuasheng, A. hypogaea cv. Shitouqi, and A. hypogaea cv. Tifrunner. The study analyzed the homologous relationships between VQs in these Arachis spp. The VQ drought-tolerant genes were detected and VQ-WRKY interactions were determined in A. hypogaea cv. Tifrunner. The results showed that tetraploid Arachis spp. retained duplicated VQs, but lost ancestral VQs after allopolyploidization. The number of VQs in A. monticola, A. hypogaea cv. Fuhuasheng, and A. hypogaea cv. Shitouqi increased relative to their diploid ancestors. RNA-seq and quantitative real-time PCR experiments confirmed that three AhTVQs tolerate drought stress in A. hypogaea cv. Tifrunner. However, evidence of VQ-WRKY interaction for drought stress response is lacking in A. hypogaea cv. Tifrunner. Nevertheless, this study identified VQ-WRKY interactions, which possibly have multiple functions in A. hypogaea cv. Tifrunner. Altogether, this study dissected Arachis VQs, providing insights into Arachis VQ evolution and drought function.

MtWRP1, a Novel Fabacean Specific Gene, Regulates Root Nodulation and Plant Growth in Medicago truncatula

Fabaceans symbiotically interact with nitrogen-fixing rhizobacteria to form root nodules. Some fabacean specific proteins play important roles in the symbiosis. WRKY-related Protein (WRP) is a novel fabacean specific protein, whose functions have not been well characterized. In this study, MtWRP1 was functionally characterized in Medicago truncatula. It contains a WRKY domain at C-terminal and a novel transmembrane (TM) domain at N-terminal, and its WRKY domain was highly similar to the N-terminal WRKY domain of the group I WRKY proteins. The TM domain was highly homologous to the eukaryotic cytochrome b561 (Cytb561) proteins from birds. Subcellular localization revealed that MtWRP1 was targeted to the Golgi apparatus through the novel TM domain. MtWRP1 was highly expressed in roots and nodules, suggesting its possible roles in the regulation of root growth and nodulation. Both MtWRP1-overexpression transgenic M. truncatula and MtWRP1 mutants showed altered root nodulation and plant growth performance. Specifically, the formation of root nodules was significantly reduced in the absence of MtWRP1. These results demonstrated that MtWRP1 plays critical roles in root nodulation and plant growth.

Genome-wide identification of the Liriodendron chinense WRKY gene family and its diverse roles in response to multiple abiotic stress

BACKGROUND

Liriodendron chinense (Lchi) is a tree species within the Magnoliaceae family and is considered a basal angiosperm. The too low or high temperature or soil drought will restrict its growth as the adverse environmental conditions, thus improving L. chinense abiotic tolerance was the key issues to study. WRKYs are a major family of plant transcription factors known to often be involved in biotic and abiotic stress responses. So far, it is still largely unknown if and how the LchiWRKY gene family is tied to regulating L. chinense stress responses. Therefore, studying the involvement of the WRKY gene family in abiotic stress regulation in L. chinense could be very informative in showing how this tree deals with such stressful conditions.

RESULTS

In this research, we performed a genome-wide analysis of the Liriodendron chinense (Lchi) WRKY gene family, studying their classification relationships, gene structure, chromosomal locations, gene duplication, cis-element, and response to abiotic stress. The 44 members of the LchiWRKY gene family contain a significant amount of sequence diversity, with their lengths ranging from 525 bp to 40,981 bp. Using classification analysis, we divided the 44 LchiWRKY genes into three phylogenetic groups (I, II, II), with group II then being further divided into five subgroups (IIa, IIb, IIc, IId, IIe). Comparative phylogenetic analysis including the WRKY families from 17 plant species suggested that LchiWRKYs are closely related to the Magnolia Cinnamomum kanehirae WRKY family, and has fewer family members than higher plants. We found the LchiWRKYs to be evenly distributed across 15 chromosomes, with their duplication events suggesting that tandem duplication may have played a major role in LchiWRKY gene expansion model. A Ka/Ks analysis indicated that they mainly underwent purifying selection and distributed in the group IId. Motif analysis showed that LchiWRKYs contained 20 motifs, and different phylogenetic groups contained conserved motif. Gene ontology (GO) analysis showed that LchiWRKYs were mainly enriched in two categories, i.e., biological process and molecular function. Two group IIc members (LchiWRKY10 and LchiWRKY37) contain unique WRKY element sequence variants (WRKYGKK and WRKYGKS). Gene structure analysis showed that most LchiWRKYs possess 3 exons and two different types of introns: the R- and V-type which are both contained within the WRKY domain (WD). Additional promoter cis-element analysis indicated that 12 cis-elements that play different functions in environmental adaptability occur across all LchiWRKY groups. Heat, cold, and drought stress mainly induced the expression of group II and I LchiWRKYs, some of which had undergone gene duplication during evolution, and more than half of which had three exons. LchiWRKY33 mainly responded to cold stress and LchiWRKY25 mainly responded to heat stress, and LchiWRKY18 mainly responded to drought stress, which was almost 4-fold highly expressed, while 5 LchiWRKYs (LchiWRKY5, LchiWRKY23, LchiWRKY14, LchiWRKY27, and LchiWRKY36) responded equally three stresses with more than 6-fold expression. Subcellular localization analysis showed that all LchiWRKYs were localized in the nucleus, and subcellular localization experiments of LchiWRKY18 and 36 also showed that these two transcription factors were expressed in the nucleus.

CONCLUSIONS

This study shows that in Liriodendron chinense, several WRKY genes like LchiWRKY33, LchiWRKY25, and LchiWRKY18, respond to cold or heat or drought stress, suggesting that they may indeed play a role in regulating the tree's response to such conditions. This information will prove a pivotal role in directing further studies on the function of the LchiWRKY gene family in abiotic stress response and provides a theoretical basis for popularizing afforestation in different regions of China.

Stress-regulated elements in Lotus spp., as a possible starting point to understand signalling networks and stress adaptation in legumes

Although legumes are of primary economic importance for human and livestock consumption, the information regarding signalling networks during plant stress response in this group is very scarce. Lotus japonicus is a major experimental model within the Leguminosae family, whereas L. corniculatus and L. tenuis are frequent components of natural and agricultural ecosystems worldwide. These species display differences in their perception and response to diverse stresses, even at the genotype level, whereby they have been used in many studies aimed at achieving a better understanding of the plant stress-response mechanisms. However, we are far from the identification of key components of their stress-response signalling network, a previous step for implementing transgenic and editing tools to develop legume stress-resilient genotypes, with higher crop yield and quality. In this review we scope a body of literature, highlighting what is currently known on the stress-regulated signalling elements so far reported in Lotus spp. Our work includes a comprehensive review of transcription factors chaperones, redox signals and proteins of unknown function. In addition, we revised strigolactones and genes regulating phytochelatins and hormone metabolism, due to their involvement as intermediates in several physiological signalling networks. This work was intended for a broad readership in the fields of physiology, metabolism, plant nutrition, genetics and signal transduction. Our results suggest that Lotus species provide a valuable information platform for the study of specific protein-protein (PPI) interactions, as a starting point to unravel signalling networks underlying plant acclimatation to bacterial and abiotic stressors in legumes. Furthermore, some Lotus species may be a source of genes whose regulation improves stress tolerance and growth when introduced ectopically in other plant species.

TaWRKY13-A Serves as a Mediator of Jasmonic Acid-Related Leaf Senescence by Modulating Jasmonic Acid Biosynthesis

Leaf senescence is crucial for crop yield and quality. Transcriptional regulation is a key step for integrating various senescence-related signals into the nucleus. However, few regulators of senescence implicating transcriptional events have been functionally characterized in wheat. Based on our RNA-seq data, we identified a WRKY transcription factor, TaWRKY13-A, that predominately expresses at senescent stages. By using the virus-induced gene silencing (VIGS) method, we manifested impaired transcription of TaWRKY13-A leading to a delayed leaf senescence phenotype in wheat. Moreover, the overexpression (OE) of TaWRKY13-A accelerated the onset of leaf senescence under both natural growth condition and darkness in Brachypodium distachyon and Arabidopsis thaliana. Furthermore, by physiological and molecular investigations, we verified that TaWRKY13-A participates in the regulation of leaf senescence via jasmonic acid (JA) pathway. The expression of JA biosynthetic genes, including AtLOX6, was altered in TaWRKY13-A-overexpressing Arabidopsis. We also demonstrated that TaWRKY13-A can interact with the promoter of AtLOX6 and TaLOX6 by using the electrophoretic mobility shift assay (EMSA) and luciferase reporter system. Consistently, we detected a higher JA level in TaWRKY13-A-overexpressing lines than that in Col-0. Moreover, our data suggested that TaWRKY13-A is partially functional conserved with AtWRKY53 in age-dependent leaf senescence. Collectively, this study manifests TaWRKY13-A as a positive regulator of JA-related leaf senescence, which could be a new clue for molecular breeding in wheat.

Comparative transcriptome analysis and identification of candidate adaptive evolution genes of Miscanthus lutarioriparius and Miscanthus sacchariflorus

Miscanthus species are perennial C4 grasses that are considered promising energy crops because of their high biomass yields, excellent adaptability and low management costs. Miscanthus lutarioriparius and Miscanthus sacchariflorus are closely related subspecies that are distributed in different habitats. However, there are only a few reports on the mechanisms by which Miscanthus adapts to different environments. Here, comparative transcriptomic and morphological analyses were used to study the evolutionary adaptation of M. lutarioriparius and M. sacchariflorus to different habitats. In total, among 7586 identified orthologs, 2060 orthologs involved in phenylpropanoid biosynthesis and plant hormones were differentially expressed between the two species. Through an analysis of the Ka/Ks ratios of the orthologs, we estimated that the divergence time between the two species was approximately 4.37 Mya. In addition, 37 candidate positively selected orthologs (PSGs) that played important roles in the adaptation of these species to different habitats were identified. Then, the expression levels of 20 PSGs in response to flooding and drought stress were analyzed, and the analysis revealed significant changes in their expression levels. These results facilitate our understanding of the evolutionary adaptation to habitats and the speciation of M. lutarioriparius and M. sacchariflorus. We hypothesise that lignin synthesis genes are the main cause of the morphological differences between the two species. In summary, the plant nonspecific phospholipase C gene family and the receptor-like protein kinase gene family played important roles in the evolution of these two species.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01030-1.

Immune response gene coexpression network analysis of Arachis hypogaea infected with Aspergillus flavus

Aspergillus flavus (A. flavus) infection and aflatoxin contamination is a major bottleneck for peanut cultivation and value chain industry. In this study, a transcriptomic network study was conducted by retrieving publically available RNA-seq datasets of resistant and susceptible peanut varieties infected by A. flavus separately to understand the peanut defense mechanism against A. flavus. The gene expression analysis revealed differentially expressed genes (DEGs) in response to the different levels of infection and coexpression network of DEGs deciphered hub genes involved in the immune process in resistant and susceptible varieties. The interplay of resistance conferring genes and cell wall related genes was observed through functional enrichment analysis in response to pathogen infection and identified few key genes such as Protein P21, R genes, Pattern Recognition Receptor genes, Pectinesterases, Laccase and Thaumatin-like protein 1b as candidate genes in imparting immune response against A. flavus.

Genome-wide identification and expression analysis of the WRKY transcription factor family in flax (Linum usitatissimum L.)

BACKGROUND

Members of the WRKY protein family, one of the largest transcription factor families in plants, are involved in plant growth and development, signal transduction, senescence, and stress resistance. However, little information is available about WRKY transcription factors in flax (Linum usitatissimum L.).

RESULTS

In this study, comprehensive genome-wide characterization of the flax WRKY gene family was conducted that led to prediction of 102 LuWRKY genes. Based on bioinformatics-based predictions of structural and phylogenetic features of encoded LuWRKY proteins, 95 LuWRKYs were classified into three main groups (Group I, II, and III); Group II LuWRKYs were further assigned to five subgroups (IIa-e), while seven unique LuWRKYs (LuWRKYs 96-102) could not be assigned to any group. Most LuWRKY proteins within a given subgroup shared similar motif compositions, while a high degree of motif composition variability was apparent between subgroups. Using RNA-seq data, expression patterns of the 102 predicted LuWRKY genes were also investigated. Expression profiling data demonstrated that most genes associated with cellulose, hemicellulose, or lignin content were predominantly expressed in stems, roots, and less in leaves. However, most genes associated with stress responses were predominantly expressed in leaves and exhibited distinctly higher expression levels in developmental stages 1 and 8 than during other stages.

CONCLUSIONS

Ultimately, the present study provides a comprehensive analysis of predicted flax WRKY family genes to guide future investigations to reveal functions of LuWRKY proteins during plant growth, development, and stress responses.

Genome-wide identification and comparative analysis of the WRKY gene family in aquatic plants and their response to abiotic stresses in giant duckweed (Spirodela polyrhiza)

WRKY is one of the largest transcription factor families across higher plant species and is involved in important biological processes and plant responses to various biotic/abiotic stresses. However, only a few investigations on WRKYs have been conducted in aquatic plants. This study first systematically analyzed the gene structure, protein properties, and phylogenetic relationship of 693 WRKYs in nine aquatic and two wetland plants at the genome-wide level. The pattern of WRKY groups in two aquatic ferns provided new evidence for the origin and evolution of WRKY genes. ARE cis-regulatory elements show an unusual high frequency in the promoter region of WRKY genes, indicating the adaptation to the aquatic habitat in aquatic plants. The WRKY gene family experienced a series of gene loss events in aquatic plants, especially group III. Further studies were conducted on the interaction network of SpWRKYs, their target genes, and non-coding RNAs. The expression profile of SpWRKYs under phosphate starvation, cold, and submergence conditions revealed that most SpWRKYs are involved in the response to abiotic stresses. Our investigations lay the foundation for further study on the mechanism of WRKYs responding to abiotic stresses in aquatic plants.

New Insights into Plant Extracellular DNA. A Study in Soybean Root Extracellular Trap

exDNA is found in various organisms, including plants. However, plant exDNA has thus far received little attention related to its origin and role in the RET (root extracellular trap). In this study, we performed the first high-throughput genomic sequencing of plant exDNA from a Fabaceae with worldwide interest: soybean (Glycine max (L.) Merr.). The origin of this exDNA was first investigated in control condition, and the results show high-coverage on organelles (mitochondria/plastid) DNA relative to nuclear DNA, as well as a mix of coding and non-coding sequences. In the second part of this study, we investigated if exDNA release was modified during an elicitation with PEP-13 (a peptide elicitor from oomycete genus Phytophthora). Our results show that treatment of roots with PEP-13 does not affect the composition of exDNA.

Genome-wide characterization of WRKY gene family in Helianthus annuus L. and their expression profiles under biotic and abiotic stresses

WRKY transcription factors play important roles in various physiological processes and stress responses in flowering plants. Sunflower (Helianthus annuus L.) is one of the important vegetable oil supplies in the world. However, the information about WRKY genes in sunflower is limited. In this study, ninety HaWRKY genes were identified and renamed according to their locations on chromosomes. Further phylogenetic analyses classified them into four main groups including a species-specific WKKY group. Besides, HaWRKY genes within the same group or subgroup generally showed similar exon-intron structures and motif compositions. The gene duplication analysis showed that five pairs of HaWRKY genes (HaWRKY8/9, HaWRKY53/54, HaWRKY65/66, HaWRKY66/67 and HaWRKY71/72) are tandem duplicated and four HaWRKY gene pairs (HaWRKY15/82, HaWRKY25/65, HaWRKY28/55 and HaWRKY50/53) are also identified as segmental duplication events, indicating that these duplication genes were contribute to the diversity and expansion of HaWRKY gene families. The dN/dS ratio of these duplicated gene pairs were also calculated to understand the evolutionary constraints. In addition, synteny analyses of sunflower WRKY genes provided deep insight to the evolution of HaWRKY genes. Transcriptomic and qRT-PCR analyses of HaWRKY genes displayed distinct expression patterns in different plant tissues, as well as under various abiotic and biotic stresses, which provide a foundation for further functional analyses of these genes. Those functional genes related to stress tolerance and quality improvement could be applied in marker assisted breeding of the crop.

Selenium nanoparticles induced variations in growth, morphology, anatomy, biochemistry, gene expression, and epigenetic DNA methylation in Capsicum annuum; an in vitro study

This study aimed to explore whether supplementation of the culture medium with selenium nanoparticles (nSe) can influence growth, biochemistry, expression of transcription factors, and epigenetic DNA methylation in Capsicum annuum. The seeds were grown in hormone-free MS culture medium supplemented with nSe (0, 0.5, 1, 10, and 30 mgL^-1) or corresponding doses of bulk type selenate (BSe). Incorporation of nSe into the medium caused variations in morphology and growth in a manner dependent on the dose and Se type. The low doses of nSe displayed growth-promoting effects, whereas nSe at 10 and 30 mgL^-1 were associated with severe toxicity and abnormality in leaf and root development. MSAP analysis confirmed the substantial variation in cytosine DNA methylation in response to the toxic dose of nSe exhibiting epigenetic modification. The nSe toxicity was associated with DNA hyper-methylations. The nSe treatments transcriptionally upregulated the bZIP1 transcription factor by an average of 3.5 folds. With a similar trend, the upregulation (mean = 9.8 folds) in the expression of the WRKY1 transcription factor resulted from the nSe application. The nSe0.5 or nSe1 treatments resulted in a significant induction (mean = 48%) in nitrate reductase activity. A high dose of nSe led to an increase in proline concentration. The nSe treatments were also associated with modifications in activities of peroxidase and catalase enzymes. Besides, the nSe utilization increased the activity of phenylalanine ammonia-lyase enzyme (mean = 76%) and concentrations of soluble phenols (mean = 51%). The toxic dose of nSe also caused abnormalities in the structure of the stem apical meristem. The nSe toxicity was also associated with inhibition in the differentiation of xylem tissues. These findings provide novel insights into the nSe-associated molecular variations in conferring the modified growth, anatomy, and metabolism.

Red elemental selenium nanoparticles mediated substantial variations in growth, tissue differentiation, metabolism, gene transcription, epigenetic cytosine DNA methylation, and callogenesis in bittermelon (Momordica charantia); an in vitro experiment

To gain a better insight into the selenium nanoparticle (nSe) benefits/toxicity, this experiment was carried out to address the behavior of bitter melon seedlings to nSe (0, 1, 4, 10, 30, and 50 mgL-1) or bulk form (selenate). Low doses of nSe increased biomass accumulation, while concentrations of 10 mgL-1 and above were associated with stem bending, impaired root meristem, and severe toxicity. Responses to nSe were distinct from that of bulk in that the nano-type exhibited a higher efficiency to stimulate growth and organogenesis than the bulk. The bulk form displayed higher phytotoxicity than the nano-type counterpart. According to the MSAP-based analysis, nSe mediated substantial variation in DNA cytosine methylation, reflecting the epigenetic modification. By increasing the concentration of nSe, the expression of the WRKY1 transcription factor linearly up-regulated (mean = 7.9-fold). Transcriptions of phenylalanine ammonia-lyase (PAL) and 4-Coumarate: CoA-ligase (4CL) genes were also induced. The nSe treatments at low concentrations enhanced the activity of leaf nitrate reductase (mean = 52%) in contrast with the treatment at toxic concentrations. The toxic concentration of nSe increased leaf proline concentration by 80%. The nSe supplement also stimulated the activities of peroxidase (mean = 35%) and catalase (mean = 10%) enzymes. The nSe-treated seedlings exhibited higher PAL activity (mean = 39%) and soluble phenols (mean = 50%). The nSe toxicity was associated with a disrupted differentiation of xylem conducting tissue. The callus formation and performance of the explants originated from the nSe-treated seedlings had a different trend than that of the control. This experiment provides new insights into the nSe-associated advantage/ cytotoxicity and further highlights the necessity of designing convincing studies to introduce novel methods for plant cell/tissue cultures and agriculture.

Identification and expression analysis of WRKY gene family under drought stress in peanut (Arachis hypogaea L.)

WRKY transcription factors play crucial roles in regulation mechanism leading to the adaption of plants to the complex environment. In this study, AhWRKY family was comprehensively analyzed using bioinformatic approaches in combination with transcriptome sequencing data of the drought-tolerant peanut variety ‘L422’. A total of 158 AhWRKY genes were identified and named according to their distribution on the chromosomes. Based on the structural features and phylogenetic analysis of AhWRKY proteins, the AhWRKY family members were classified into three (3) groups, of which group II included five (5) subgroups. Results of structure and conserved motifs analysis for the AhWRKY genes confirmed the accuracy of the clustering analysis. In addition, 12 tandem and 136 segmental duplication genes were identified. The results indicated that segmental duplication events were the main driving force in the evolution of AhWRKY family. Collinearity analysis found that 32 gene pairs existed between Arachis hypogaea and two diploid wild ancestors (Arachis duranensis and Arachis ipaensis), which provided valuable clues for phylogenetic characteristics of AhWRKY family. Furthermore, 19 stress-related cis-acting elements were found in the promoter regions. During the study of gene expression level of AhWRKY family members in response to drought stress, 73 differentially expressed AhWRKY genes were obtained to have been influenced by drought stress. These results provide fundamental insights for further study of WRKY genes in peanut drought resistance.

Genome-wide identification and expression analysis of WRKY transcription factors in pearl millet (Pennisetum glaucum) under dehydration and salinity stress

Background

Plants have developed various sophisticated mechanisms to cope up with climate extremes and different stress conditions, especially by involving specific transcription factors (TFs). The members of the WRKY TF family are well known for their role in plant development, phytohormone signaling and developing resistance against biotic or abiotic stresses. In this study, we performed a genome-wide screening to identify and analyze the WRKY TFs in pearl millet (Pennisetum glaucum; PgWRKY), which is one of the most widely grown cereal crops in the semi-arid regions.

Results

A total number of 97 putative PgWRKY proteins were identified and classified into three major Groups (I-III) based on the presence of WRKY DNA binding domain and zinc-finger motif structures. Members of Group II have been further subdivided into five subgroups (IIa-IIe) based on the phylogenetic analysis. In-silico analysis of PgWRKYs revealed the presence of various cis-regulatory elements in their promoter region like ABRE, DRE, ERE, EIRE, Dof, AUXRR, G-box, etc., suggesting their probable involvement in growth, development and stress responses of pearl millet. Chromosomal mapping evidenced uneven distribution of identified 97 PgWRKY genes across all the seven chromosomes of pearl millet. Synteny analysis of PgWRKYs established their orthologous and paralogous relationship among the WRKY gene family of Arabidopsis thaliana, Oryza sativa and Setaria italica. Gene ontology (GO) annotation functionally categorized these PgWRKYs under cellular components, molecular functions and biological processes. Further, the differential expression pattern of PgWRKYs was noticed in different tissues (leaf, stem, root) and under both drought and salt stress conditions. The expression pattern of PgWRKY33, PgWRKY62 and PgWRKY65 indicates their probable involvement in both dehydration and salinity stress responses in pearl millet.

Conclusion

Functional characterization of identified PgWRKYs can be useful in delineating their role behind the natural stress tolerance of pearl millet against harsh environmental conditions. Further, these PgWRKYs can be employed in genome editing for millet crop improvement.

A Comprehensive Transcriptome-Wide Identification and Screening of WRKY Gene Family Engaged in Abiotic Stress in Glycyrrhiza glabra

The study reports 147 full-length WRKY genes based on the transcriptome analysis of Glycyrrhiza genus (G. glabra and G. uralensis). Additional motifs in G. glabra included DivIVA (GgWRKY20) and SerS Superfamily (GgWRKY21) at the C-terminal, and Coat family motifs (GgWRKY55) at the N-terminal of the proteins, while Exo70 exo cyst complex subunit of 338 amino acid (GuWRKY9) was present at the N-terminal of G. uralensis only. Plant Zn cluster super-family domain (17 WRKYs) and bZIP domain (2 WRKYs) were common between the two species. Based on the number of WRKY domains, sequence alignment and phylogenesis, the study identified GuWRKY27 comprising of 3 WRKY domains in G. uralensis and a new subgroup-IIf (10 members), having novel zinc finger pattern (C-X4-C-X22-HXH) in G. glabra. Multiple WRKY binding domains (1-11) were identified in the promoter regions of the GgWRKY genes indicating strong interacting network between the WRKY proteins. Tissue-specific expression of 25 GgWRKYs, under normal and treated conditions, revealed 11 of the 18 induction factor triggered response corroborating to response observed in AtWRKYs. The study identified auxin-responsive GgWRKY 55 & GgWRKY38; GA3 responsive GgWRKYs15&59 in roots and GgWRKYs8, 20, 38, 57 &58 in the shoots of the treated plant. GgWRKYs induced under various stresses included GgWRKY33 (cold), GgWRKY4 (senescence), GgWRKYs2, 28 & 33 (salinity) and GgWRKY40 (wounding). Overall, 23 GgWRKYs responded to abiotic stress, and 17 WRKYs were induced by hormonal signals. Of them 13 WRKYs responded to both suggesting inter-connection between hormone signalling and stress response. The present study will help in understanding the transcriptional reprogramming, protein-protein interaction and cross-regulation during stress and other physiological processes in the plant.

Evolutionary balance between LRR domain loss and young NBS-LRR genes production governs disease resistance in Arachis hypogaea cv. Tifrunner

BACKGROUND

Cultivated peanut (Arachis hypogaea L.) is an important oil and protein crop, but it has low disease resistance; therefore, it is important to reveal the number, sequence features, function, and evolution of genes that confer resistance. Nucleotide-binding site-leucine-rich repeats (NBS-LRRs) are resistance genes that are involved in response to various pathogens.

RESULTS

We identified 713 full-length NBS-LRRs in A. hypogaea cv. Tifrunner. Genetic exchange events occurred on NBS-LRRs in A. hypogaea cv. Tifrunner, which were detected in the same subgenomes and also found in different subgenomes. Relaxed selection acted on NBS-LRR proteins and LRR domains in A. hypogaea cv. Tifrunner. Using quantitative trait loci (QTL), we found that NBS-LRRs were involved in response to late leaf spot, tomato spotted wilt virus, and bacterial wilt in A. duranensis (2 NBS-LRRs), A. ipaensis (39 NBS-LRRs), and A. hypogaea cv. Tifrunner (113 NBS-LRRs). In A. hypogaea cv. Tifrunner, 113 NBS-LRRs were classified as 75 young and 38 old NBS-LRRs, indicating that young NBS-LRRs were involved in response to disease after tetraploidization. However, compared to A. duranensis and A. ipaensis, fewer LRR domains were found in A. hypogaea cv. Tifrunner NBS-LRR proteins, partly explaining the lower disease resistance of the cultivated peanut.

CONCLUSIONS

Although relaxed selection acted on NBS-LRR proteins and LRR domains, LRR domains were preferentially lost in A. hypogaea cv. Tifrunner compared to A. duranensis and A. ipaensis. The QTL results suggested that young NBS-LRRs were important for resistance against diseases in A. hypogaea cv. Tifrunner. Our results provid insight into the greater susceptibility of A. hypogaea cv. Tifrunner to disease compared to A. duranensis and A. ipaensis.

Candidate genes expression profiling during wilting in chickpea caused by Fusarium oxysporum f. sp. ciceris race 5

Chickpea production may be seriously threatened by Fusarium wilt, a disease caused by the soil-borne fungus Fusarium oxysporum f. sp. ciceris. F. oxysporum race 5 is the most important race in the Mediterranean basin. Recently, the region responsible for resistance race 5 has been delimited within a region on chromosome 2 that spans 820 kb. To gain a better understanding of this genomic region, we used a transcriptomic approach based on quantitative real-time PCR to analyze the expression profiles of 22 selected candidate genes. We used a pair of near-isogenic lines (NILs) differing in their sensitivity to Fusarium race 5 (resistant vs susceptible) to monitor the transcriptional changes over a time-course experiment (24, 48, and 72 hours post inoculation, hpi). Qualitative differences occurred during the timing of regulation. A cluster of 12 genes were induced by the resistant NIL at 24 hpi, whereas a second cluster contained 9 genes induced by the susceptible NIL at 48 hpi. Their possible functions in the molecular defence of chickpea is discussed. Our study provides new insight into the molecular defence against Fusarium race 5 and demonstrates that development of NILs is a rich resource to facilitate the detection of candidate genes. The new genes regulated here may be useful against other Fusarium races.

The characteristic of Arachis duranensis-specific genes and their potential function

Arachis species produce flowers aerially, and then grow into the ground, where they develop into fruits; a feature that is unique to Arachis species. We hypothesized that Arachis species evolved genes specifically involved in the control of aerial flowers and the formation of underground fruits. Arachis duranensis is more resistant to biotic and abiotic stressors. Here, we compared different legume species and identified Arachis duranensis-specific genes. We analyzed gene expression patterns, base substitution patterns and sequence features between genes that are conserved across legume plants and A. duranensis-specific genes. Furthermore, we tested the role of A. duranensis-specific genes during seed development, response to nematode Meloidogyne arenaria infection and drought stress. We found that A. duranensis-specific genes had characteristics of young genes. The gene expression level and breadth were lower in the A. duranensis-specific genes compared to conserved genes. The A. duranensis-specific genes had higher codon usage bias than conserved genes, and the polypeptide length and GC content at the three codon sites were lower compared to conserved genes. Of the A. duranensis-specific genes, single-copy and duplicated genes had different features. The RNA-seq result showed A. duranensis-specific genes were involved in seed development, as well as response to nematode infection and drought stress. In addition, we detected asymmetric functions in A. duranensis-specific duplicated genes in response to nematode infection and drought stress.

GmWRKY16 Enhances Drought and Salt Tolerance Through an ABA-Mediated Pathway in Arabidopsis thaliana

The WRKY transcription factors (TFs) are one of the largest families of TFs in plants and play multiple roles in plant development and stress response. In the present study, GmWRKY16 encoding a WRKY transcription factor in soybean was functionally characterized in Arabidopsis. GmWRKY16 is a nuclear protein that contains a highly conserved WRKY domain and a C2H2 zinc-finger structure, and has the characteristics of transcriptional activation ability, presenting a constitutive expression pattern with relative expression levels of over fourfold in the old leaves, flowers, seeds and roots of soybean. The results of quantitative real time polymerase chain reaction (qRT-PCR) showed that GmWRKY16 could be induced by salt, alkali, ABA, drought and PEG-6000. As compared with the control, overexpression of GmWRKY16 in Arabidopsis increased the seed germination rate and root growth of seedlings in transgenic lines under higher concentrations of mannitol, NaCl and ABA. In the meantime, GmWRKY16 transgenic lines showed over 75% survival rate after rehydration and enhanced Arabidopsis tolerance to salt and drought with higher proline and lower MDA accumulation, less water loss of the detached leaves, and accumulated more endogenous ABA than the control under stress conditions. Further studies showed that AtWRKY8, KIN1, and RD29A were induced in GmWRKY16 transgenic plants under NaCl treatment. The expressions of the ABA biosynthesis gene (NCED3), signaling genes (ABI1, ABI2, ABI4, and ABI5), responsive genes (RD29A, COR15A, COR15B, and RD22) and stress-related marker genes (KIN1, LEA14, LEA76, and CER3) were regulated in transgenic lines under drought stress. In summary, these results suggest that GmWRKY16 as a WRKY TF may promote tolerance to drought and salt stresses through an ABA-mediated pathway.