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

Overexpression of a pearl millet WRKY transcription factor gene, PgWRKY74, in Arabidopsis retards shoot growth under dehydration and salinity-stressed conditions

Pearl millet (Cenchrus americanus) is a cereal crop that can tolerate high temperatures, drought, and low-fertility conditions where other crops lose productivity. However, genes regulating this ability are largely unknown. Transcription factors (TFs) regulate transcription of their target genes, regulate downstream biological processes, and thus are candidates for regulators of such tolerance of pearl millet. PgWRKY74 encodes a group IIc WRKY TF in pearl millet and is downregulated by drought. PgWRKY74 may have a role in drought tolerance. The objective of this study was to gain insights into the physiological and biochemical functions of PgWRKY74. Yeast one-hybrid and gel shift assays were performed to examine transcriptional activation potential and deoxyribonucleic acid (DNA)-binding ability, respectively. Transgenic Arabidopsis thaliana plants overexpressing PgWRKY74-green fluorescent protein (GFP) fusion gene were generated and tested for growth and stress-responsive gene expression under mannitol and NaCl-stressed conditions. A construct with PgWRKY74 enabled yeast reporter cells to survive on test media in the yeast one-hybrid assays. The electrophoretic mobility of DNA with putative WRKY TF-binding motifs was lower in the presence of a recombinant PgWRKY74 protein than its absence. The PgWRKY74-GFP-overexpressing Arabidopsis plants exhibited smaller rosette areas than did wild-type plants under mannitol-stressed and NaCl-stressed conditions, and exhibited weaker expression of RD29B, which is induced by the stress-related phytohormone abscisic acid (ABA), under the mannitol-stressed condition. PgWRKY74 have transcriptional activation potential and DNA-binding ability, and can negatively regulate plant responses to mannitol and NaCl stresses, possibly by decreasing ABA levels or ABA sensitivity.

Realizing visionary goals for the International Year of Millet (IYoM): accelerating interventions through advances in molecular breeding and multiomics resources

MAIN CONCLUSION

Leveraging advanced breeding and multi-omics resources is vital to position millet as an essential "nutricereal resource," aligning with IYoM goals, alleviating strain on global cereal production, boosting resilience to climate change, and advancing sustainable crop improvement and biodiversity. The global challenges of food security, nutrition, climate change, and agrarian sustainability demand the adoption of climate-resilient, nutrient-rich crops to support a growing population amidst shifting environmental conditions. Millets, also referred to as "Shree Anna," emerge as a promising solution to address these issues by bolstering food production, improving nutrient security, and fostering biodiversity conservation. Their resilience to harsh environments, nutritional density, cultural significance, and potential to enhance dietary quality index made them valuable assets in global agriculture. Recognizing their pivotal role, the United Nations designated 2023 as the "International Year of Millets (IYoM 2023)," emphasizing their contribution to climate-resilient agriculture and nutritional enhancement. Scientific progress has invigorated efforts to enhance millet production through genetic and genomic interventions, yielding a wealth of advanced molecular breeding technologies and multi-omics resources. These advancements offer opportunities to tackle prevailing challenges in millet, such as anti-nutritional factors, sensory acceptability issues, toxin contamination, and ancillary crop improvements. This review provides a comprehensive overview of molecular breeding and multi-omics resources for nine major millet species, focusing on their potential impact within the framework of IYoM. These resources include whole and pan-genome, elucidating adaptive responses to abiotic stressors, organelle-based studies revealing evolutionary resilience, markers linked to desirable traits for efficient breeding, QTL analysis facilitating trait selection, functional gene discovery for biotechnological interventions, regulatory ncRNAs for trait modulation, web-based platforms for stakeholder communication, tissue culture techniques for genetic modification, and integrated omics approaches enabled by precise application of CRISPR/Cas9 technology. Aligning these resources with the seven thematic areas outlined by IYoM catalyzes transformative changes in millet production and utilization, thereby contributing to global food security, sustainable agriculture, and enhanced nutritional consequences.

Milletomics: a metabolomics centered integrated omics approach toward genetic progression

Producing alternative staple foods like millet will be essential to feeding ten billion people by 2050. The increased demand for millet is driving researchers to improve its genetic variation. Millets include protein, dietary fiber, phenolic substances, and flavonoid components. Its climate resilience makes millet an appealing crop for agronomic sustainability. Integrative omics technologies could potentially identify and develop millets with desirable phenotypes that may have high agronomic value. Millets' salinity and drought tolerance have been enhanced using transcriptomics. In foxtail, finger, and pearl millet, proteomics has discovered salt-tolerant protein, phytohormone-focused protein, and drought tolerance. Metabolomics studies have revealed that certain metabolic pathways including those involving lignin, flavonoids, phenylpropanoid, and lysophospholipids are critical for many processes, including seed germination, photosynthesis, energy metabolism, and the synthesis of bioactive chemicals necessary for drought tolerance. Metabolomics integration with other omics revealed metabolome engineering and trait-specific metabolite creation. Integrated metabolomics and ionomics are still in the development stage, but they could potentially assist in comprehending the pathway of ionomers to control nutrient levels and biofortify millet. Epigenomic analysis has shown alterations in DNA methylation patterns and chromatin structure in foxtail and pearl millets in response to abiotic stress. Whole-genome sequencing utilizing next-generation sequencing is the most proficient method for finding stress-induced phytoconstituent genes. New genome sequencing enables novel biotechnological interventions including genome-wide association, mutation-based research, and other omics approaches. Millets can breed more effectively by employing next-generation sequencing and genotyping by sequencing, which may mitigate climate change. Millet marker-assisted breeding has advanced with high-throughput markers and combined genotyping technologies.

Regulatory Dynamics of Plant Hormones and Transcription Factors under Salt Stress

The negative impacts of soil salinization on ion homeostasis provide a significant global barrier to agricultural production and development. Plant physiology and biochemistry are severely affected by primary and secondary NaCl stress impacts, which damage cellular integrity, impair water uptake, and trigger physiological drought. Determining how transcriptional factors (TFs) and hormone networks are regulated in plants in response to salt stress is necessary for developing crops that tolerate salt. This study investigates the complex mechanisms of several significant TF families that influence plant responses to salt stress, involving AP2/ERF, bZIP, NAC, MYB, and WRKY. It demonstrates how these transcription factors (TFs) help plants respond to the detrimental effects of salinity by modulating gene expression through mechanisms including hormone signaling, osmotic stress pathway activation, and ion homeostasis. Additionally, it explores the hormonal imbalances triggered by salt stress, which entail complex interactions among phytohormones like jasmonic acid (JA), salicylic acid (SA), and abscisic acid (ABA) within the hormonal regulatory networks. This review highlights the regulatory role of key transcription factors in salt-stress response, and their interaction with plant hormones is crucial for developing genome-edited crops that can enhance agricultural sustainability and address global food security challenges.

Comprehensive analysis of B3 family genes in pearl millet (Pennisetum glaucum) and the negative regulator role of PgRAV-04 in drought tolerance

Introduction

Members of the plant-specific B3 transcription factor superfamily play crucial roles in various plant growth and developmental processes. Despite numerous valuable studies on B3 genes in other species, little is known about the B3 superfamily in pearl millet.

Methods and results

Here, through comparative genomic analysis, we identified 70 B3 proteins in pearl millet and categorized them into four subfamilies based on phylogenetic affiliations: ARF, RAV, LAV, and REM. We also mapped the chromosomal locations of these proteins and analyzed their gene structures, conserved motifs, and gene duplication events, providing new insights into their potential functional interactions. Using transcriptomic sequencing and real-time quantitative PCR, we determined that most PgB3 genes exhibit upregulated expression under drought and high-temperature stresses, indicating their involvement in stress response regulation. To delve deeper into the abiotic stress roles of the B3 family, we focused on a specific gene within the RAV subfamily, PgRAV-04, cloning it and overexpressing it in tobacco. PgRAV-04 overexpression led to increased drought sensitivity in the transgenic plants due to decreased proline levels and peroxidase activity.

Discussion

This study not only adds to the existing body of knowledge on the B3 family's characteristics but also advances our functional understanding of the PgB3 genes in pearl millet, reinforcing the significance of these factors in stress adaptation mechanisms.

Genome-Wide Identification, Characterisation, and Evolution of the Transcription Factor WRKY in Grapevine (Vitis vinifera): New View and Update

WRKYs are a multigenic family of transcription factors that are plant-specific and involved in the regulation of plant development and various stress response processes. However, the evolution of WRKY genes is not fully understood. This family has also been incompletely studied in grapevine, and WRKY genes have been named with different numbers in different studies, leading to great confusion. In this work, 62 Vitis vinifera WRKY genes were identified based on six genomes of different cultivars. All WRKY genes were numbered according to their chromosomal location, and a complete revision of the numbering was performed. Amino acid variability between different cultivars was assessed for the first time and was greater than 5% for some WRKYs. According to the gene structure, all WRKYs could be divided into two groups: more exons/long length and fewer exons/short length. For the first time, some chimeric WRKY genes were found in grapevine, which may play a specific role in the regulation of different processes: VvWRKY17 (an N-terminal signal peptide region followed by a non-cytoplasmic domain) and VvWRKY61 (Frigida-like domain). Five phylogenetic clades A-E were revealed and correlated with the WRKY groups (I, II, III). The evolution of WRKY was studied, and we proposed a WRKY evolution model where there were two dynamic phases of complexity and simplification in the evolution of WRKY.

Genome-wide characterization of the NBLRR gene family provides evolutionary and functional insights into blast resistance in pearl millet (Cenchrus americanus (L.) Morrone)

MAIN CONCLUSION

The investigation is the first report on genome-wide identification and characterization of NBLRR genes in pearl millet. We have shown the role of gene loss and purifying selection in the divergence of NBLRRs in Poaceae lineage and candidate CaNBLRR genes for resistance to Magnaporthe grisea infection. Plants have evolved multiple integral mechanisms to counteract the pathogens' infection, among which plant immunity through NBLRR (nucleotide-binding site, leucine-rich repeat) genes is at the forefront. The genome-wide mining in pearl millet (Cenchrus americanus (L.) Morrone) revealed 146 CaNBLRRs. The variation in the branch length of NBLRRs showed the dynamic nature of NBLRRs in response to evolving pathogen races. The orthology of NBLRRs showed a predominance of many-to-one orthologs, indicating the divergence of NBLRRs in the pearl millet lineage mainly through gene loss events followed by gene gain through single-copy duplications. Further, the purifying selection (Ka/Ks < 1) shaped the expansion of NBLRRs within the lineage of pear millet and other members of Poaceae. Presence of cis-acting elements, viz. TCA element, G-box, MYB, SARE, ABRE and conserved motifs annotated with P-loop, kinase 2, RNBS-A, RNBS-D, GLPL, MHD, Rx-CC and LRR suggests their putative role in disease resistance and stress regulation. The qRT-PCR analysis in pearl millet lines showing contrasting responses to Magnaporthe grisea infection identified CaNBLRR20, CaNBLRR33, CaNBLRR46 CaNBLRR51, CaNBLRR78 and CaNBLRR146 as putative candidates. Molecular docking showed the involvement of three and two amino acid residues of LRR domains forming hydrogen bonds (histidine, arginine and threonine) and salt bridges (arginine and lysine) with effectors. Whereas 14 and 20 amino acid residues of CaNBLRR78 and CaNBLRR20 showed hydrophobic interactions with 11 and 9 amino acid residues of effectors, Mg.00g064570.m01 and Mg.00g006570.m01, respectively. The present investigation gives a comprehensive overview of CaNBLRRs and paves the foundation for their utility in pearl millet resistance breeding through understanding of host-pathogen interactions.

Major transcription factor families at the nexus of regulating abiotic stress response in millets: a comprehensive review

Millets stand out as a sustainable crop with the potential to address the issues of food insecurity and malnutrition. These small-seeded, drought-resistant cereals have adapted to survive a broad spectrum of abiotic stresses. Researchers are keen on unravelling the regulatory mechanisms that empower millets to withstand environmental adversities. The aim is to leverage these identified genetic determinants from millets for enhancing the stress tolerance of major cereal crops through genetic engineering or breeding. This review sheds light on transcription factors (TFs) that govern diverse abiotic stress responses and play role in conferring tolerance to various abiotic stresses in millets. Specifically, the molecular functions and expression patterns of investigated TFs from various families, including bHLH, bZIP, DREB, HSF, MYB, NAC, NF-Y and WRKY, are comprehensively discussed. It also explores the potential of TFs in developing stress-tolerant crops, presenting a comprehensive discussion on diverse strategies for their integration.

Identification of WRKY gene family in Dioscorea opposita Thunb. reveals that DoWRKY71 enhanced the tolerance to cold and ABA stress

WRKY transcription factors constitute one of the largest plant-specific gene families, regulating various aspects of plant growth, development, physiological processes, and responses to abiotic stresses. This study aimed to comprehensively analyze the WRKY gene family of yam (Dioscorea opposita Thunb.), to understand their expression patterns during the growth and development process and their response to different treatments of yam and analyze the function of DoWRKY71 in detail. A total of 25 DoWRKY genes were identified from the transcriptome of yam, which were divided into six clades (I, IIa, IIc, IId, IIe, III) based on phylogenetic analysis. The analysis of conserved motifs revealed 10 motifs, varying in length from 16 to 50 amino acids. Based on real-time quantitative PCR (qRT-PCR) analysis, DoWRKY genes were expressed at different stages of growth and development and responded differentially to various abiotic stresses. The expression level of DoWRKY71 genes was up-regulated in the early stage and then down-regulated in tuber enlargement. This gene showed responsiveness to cold and abiotic stresses, such as abscisic acid (ABA) and methyl jasmonate (MeJA). Therefore, further study was conducted on this gene. Subcellular localization analysis revealed that the DoWRKY71 protein was localized in the nucleus. Moreover, the overexpression of DoWRKY71 enhanced the cold tolerance of transgenic tobacco and promoted ABA mediated stomatal closure. This study presents the first systematic analysis of the WRKY gene family in yam, offering new insights for studying WRKY transcription factors in yam. The functional study of DoWRKY71 lays theoretical foundation for further exploring the regulatory function of the DoWRKY71 gene in the growth and development related signaling pathway of yam.

Identification of WRKY Family Members and Characterization of the Low-Temperature-Stress-Responsive WRKY Genes in Luffa (Luffa cylindrica L.)

The plant-specific WRKY transcription factor family members have diverse regulatory effects on the genes associated with many plant processes. Although the WRKY proteins in Arabidopsis thaliana and other species have been thoroughly investigated, there has been relatively little research on the WRKY family in Luffa cylindrica, which is one of the most widely grown vegetables in China. In this study, we performed a genome-wide analysis to identify L. cylindrica WRKY genes, which were subsequently classified and examined in terms of their gene structures, chromosomal locations, promoter cis-acting elements, and responses to abiotic stress. A total of 62 LcWRKY genes (471-2238 bp) were identified and divided into three phylogenetic groups (I, II, and III), with group II further divided into five subgroups (IIa, IIb, IIc, IId, and IIe) in accordance with the classification in other plants. The LcWRKY genes were unevenly distributed across 13 chromosomes. The gene structure analysis indicated that the LcWRKY genes contained 0-11 introns (average of 4.4). Moreover, 20 motifs were detected in the LcWRKY proteins with conserved motifs among the different phylogenetic groups. Two subgroup IIc members (LcWRKY16 and LcWRKY31) contained the WRKY sequence variant WRKYGKK. Additionally, nine cis-acting elements related to diverse responses to environmental stimuli were identified in the LcWRKY promoters. The subcellular localization analysis indicated that three LcWRKY proteins (LcWRKY43, LcWRKY7, and LcWRKY23) are localized in the nucleus. The tissue-specific LcWRKY expression profiles reflected the diversity in LcWRKY expression. The RNA-seq data revealed the effects of low-temperature stress on LcWRKY expression. The cold-induced changes in expression were verified via a qRT-PCR analysis of 24 differentially expressed WRKY genes. Both LcWRKY7 and LcWRKY12 were highly responsive to the low-temperature treatment (approximately 110-fold increase in expression). Furthermore, the LcWRKY8, LcWRKY12, and LcWRKY59 expression levels increased by more than 25-fold under cold conditions. Our findings will help clarify the evolution of the luffa WRKY family while also providing valuable insights for future studies on WRKY functions.

"Genome-wide identification of bZIP gene family in Pearl millet and transcriptional profiling under abiotic stress, phytohormonal treatments; and functional characterization of PgbZIP9"

Abiotic stresses are major constraints in crop production, and are accountable for more than half of the total crop loss. Plants overcome these environmental stresses using coordinated activities of transcription factors and phytohormones. Pearl millet an important C4 cereal plant having high nutritional value and climate resilient features is grown in marginal lands of Africa and South-East Asia including India. Among several transcription factors, the basic leucine zipper (bZIP) is an important TF family associated with diverse biological functions in plants. In this study, we have identified 98 bZIP family members (PgbZIP) in pearl millet. Phylogenetic analysis divided these PgbZIP genes into twelve groups (A-I, S, U and X). Motif analysis has shown that all the PgbZIP proteins possess conserved bZIP domains and the exon-intron organization revealed conserved structural features among the identified genes. Cis-element analysis, RNA-seq data analysis, and real-time expression analysis of PgbZIP genes suggested the potential role of selected PgbZIP genes in growth/development and abiotic stress responses in pearl millet. Expression profiling of selected PgbZIPs under various phytohormones (ABA, SA and MeJA) treatment showed differential expression patterns of PgbZIP genes. Further, PgbZIP9, a homolog of AtABI5 was found to localize in the nucleus and modulate gene expression in pearl millet under stresses. Our present findings provide a better understanding of bZIP genes in pearl millet and lay a good foundation for the further functional characterization of multi-stress tolerant PgbZIP genes, which could become efficient tools for crop improvement.

Genome-Wide Identification and Transcriptional Analysis of AP2/ERF Gene Family in Pearl Millet (Pennisetum glaucum)

The apetala2/ethylene response factor (AP2/ERF) gene family plays a crucial role in regulating plant growth and development and responding to different abiotic stresses (e.g., drought, heat, cold, and salinity). However, the knowledge of the ERF family in pearl millet remains limited. Here, a total of 167 high-confidence PgERF genes are identified and divided into five subgroups based on gene-conserved structure and phylogenetic analysis. Forty-one pairs of segmental duplication are found using collinear analysis. Nucleotide substitution analysis reveals these duplicated pairs are under positive purification, indicating they are actively responding to natural selection. Comprehensive transcriptomic analysis reveals that PgERF genesare preferentially expressed in the imbibed seeds and stem (tilling stage) and respond to heat, drought, and salt stress. Prediction of the cis-regulatory element by the PlantCARE program indicates that PgERF genes are involved in responses to environmental stimuli. Using reverse transcription quantitative real-time PCR (RT-qPCR), expression profiles of eleven selected PgERF genes are monitored in various tissues and during different abiotic stresses. Transcript levels of each PgERF gene exhibit significant changes during stress treatments. Notably, the PgERF7 gene is the only candidate that can be induced by all adverse conditions. Furthermore, four PgERF genes (i.e., PgERF22, PgERF37, PgERF88, and PgERF155) are shown to be involved in the ABA-dependent signaling pathway. These results provide useful bioinformatic and transcriptional information for understanding the roles of the pearl millet ERF gene family in adaptation to climate change.

Unraveling the involvement of WRKY TFs in regulating plant disease defense signaling

MAIN CONCLUSION

This review article explores the intricate role, regulation, and signaling mechanisms of WRKY TFs in response to biotic stress, particularly emphasizing their pivotal role in the trophism of plant-pathogen interactions. Transcription factors (TFs) play a vital role in governing both plant defense and development by controlling the expression of various downstream target genes. Early studies have shown the differential expression of certain WRKY transcription factors by microbial infections. Several transcriptome-wide studies later demonstrated that diverse sets of WRKYs are significantly activated in the early stages of viral, bacterial, and fungal infections. Furthermore, functional investigations indicated that overexpression or silencing of certain WRKY genes in plants can drastically alter disease symptoms as well as pathogen multiplication rates. Hence the new aspects of pathogen-triggered WRKY TFs mediated regulation of plant defense can be explored. The already recognized roles of WRKYs include transcriptional regulation of defense-related genes, modulation of hormonal signaling, and participation in signal transduction pathways. Some WRKYs have been shown to directly bind to pathogen effectors, acting as decoys or resistance proteins. Notably, the signaling molecules like salicylic acid, jasmonic acid, and ethylene which are associated with plant defense significantly increase the expression of several WRKYs. Moreover, induction of WRKY genes or heightened WRKY activities is also observed during ISR triggered by the beneficial microbes which protect the plants from subsequent pathogen infection. To understand the contribution of WRKY TFs towards disease resistance and their exact metabolic functions in infected plants, further studies are required. This review article explores the intrinsic transcriptional regulation, signaling mechanisms, and hormonal crosstalk governed by WRKY TFs in plant disease defense response, particularly emphasizing their specific role against different biotrophic, hemibiotrophic, and necrotrophic pathogen infections.

Plant salinity stress, sensing, and its mitigation through WRKY

Salinity or salt stress has deleterious effects on plant growth and development. It imposes osmotic, ionic, and secondary stresses, including oxidative stress on the plants and is responsible for the reduction of overall crop productivity and therefore challenges global food security. Plants respond to salinity, by triggering homoeostatic mechanisms that counter salt-triggered disturbances in the physiology and biochemistry of plants. This involves the activation of many signaling components such as SOS pathway, ABA pathway, and ROS and osmotic stress signaling. These biochemical responses are accompanied by transcriptional modulation of stress-responsive genes, which is mostly mediated by salt-induced transcription factor (TF) activity. Among the TFs, the multifaceted significance of WRKY proteins has been realized in many diverse avenues of plants' life including regulation of plant stress response. Therefore, in this review, we aimed to highlight the significance of salinity in a global perspective, the mechanism of salt sensing in plants, and the contribution of WRKYs in the modulation of plants' response to salinity stress. This review will be a substantial tool to investigate this problem in different perspectives, targeting WRKY and offering directions to better manage salinity stress in the field to ensure food security.

Genome-Wide Identification of Bilberry WRKY Transcription Factors: Go Wild and Duplicate

WRKY transcription factor genes compose an important family of transcriptional regulators that are present in several plant species. According to previous studies, these genes can also perform important roles in bilberry (Vaccinium myrtillus L.) metabolism, making it essential to deepen our understanding of fruit ripening regulation and anthocyanin biosynthesis. In this context, the detailed characterization of these proteins will provide a comprehensive view of the functional features of VmWRKY genes in different plant organs and in response to different intensities of light. In this study, the investigation of the complete genome of the bilberry identified 76 VmWRKY genes that were evaluated and distributed in all twelve chromosomes. The proteins encoded by these genes were classified into four groups (I, II, III, and IV) based on their conserved domains and zinc finger domain types. Fifteen pairs of VmWRKY genes in segmental duplication and four pairs in tandem duplication were detected. A cis element analysis showed that all promoters of the VmWRKY genes contain at least one potential cis stress-response element. Differential expression analysis of RNA-seq data revealed that VmWRKY genes from bilberry show preferential or specific expression in samples. These findings provide an overview of the functional characterization of these proteins in bilberry.

Multi-algorithm cooperation research of WRKY genes under nitrogen stress in Panax notoginseng

WRKY transcription factors play an important role in the immune system and the innate defense response of plants. WRKY transcription factors have great feedback on nitrogen stress. In this study, bioinformatics was used to detect the WRKYs of Panax notoginseng (PnWRKYs). The response of PnWRKYs under nitrogen stress was also well studied. PnWRKYs were distributed on 11 chromosomes. According to PnWRKY and Arabidopsis thaliana WRKY (AtWRKY) domains, these PnWRKY proteins were divided into three groups by phylogenetic analysis. MEME analysis showed that almost every member contained motif 1 and motif 2. PlantCARE online predicted the cis-acting elements of the promoter. PnWRKY gene family members obtained 22 pairs of repeat fragments by collinearity analysis. The expression levels of PnWRKYs in different parts (roots, flowers, and leafs) were analyzed by the gene expression pattern. They reflected tissue-specific expressions. The qRT-PCR experiments were used to detect 74 PnWRKYs under nitrogen stress. The results showed that the expression levels of 8 PnWRKYs were significantly induced. The PnWRKY gene family may be involved in biotic/abiotic stresses and hormone induction. This study will not only lay the foundation to explore the functions of PnWRKYs but also provide candidate genes for the future improvement of P. notoginseng.

The potentialities of omics resources for millet improvement

Millets are nutrient-rich (nutri-rich) cereals with climate resilience attributes. However, its full productive potential is not realized due to the lack of a focused yield improvement approach, as evidenced by the available literature. Also, the lack of well-characterized genomic resources significantly limits millet improvement. But the recent availability of genomic data and advancement in omics tools has shown its enormous potential to enhance the efficiency and precision faced by conventional breeding in millet improvement. The development of high throughput genotyping platforms based on next-generation sequencing (NGS) has provided a low-cost method for genomic information, specifically for neglected nutri-rich cereals with the availability of a limited number of reference genome sequences. NGS has created new avenues for millet biotechnological interventions such as mutation-based study, GWAS, GS, and other omics technologies. The simultaneous discovery of high-throughput markers and multiplexed genotyping platform has aggressively aided marker-assisted breeding for millet improvement. Therefore, omics technology offers excellent opportunities to explore and combine useful variations for targeted traits that could impart high nutritional value to high-yielding cultivars under changing climatic conditions. In millet improvement, an in-depth account of NGS, integrating genomics data with different biotechnology tools, is reviewed in this context.

Phylogenetic trees, conserved motifs and predicted subcellular localization for transcription factor families in pearl millet

OBJECTIVES

Pearl millet (Pennisetum glaucum) is a cereal crop that is tolerant to a high temperature, a drought and a nutrient-poor condition. Characterizing pearl millet proteins can help to improve productivity of pearl millet and other crops. Transcription factors in general are proteins that regulate transcription of their target genes and thereby regulate diverse processes. Some transcription factor families in pearl millet were characterized in previous studies, but most of them are not. The objective of the data presented was to characterize amino acid sequences for most transcription factors in pearl millet.

DATA DESCRIPTION

Sequences of 2395 pearl millet proteins that have transcription factor-associated domains were extracted. Subcellular and suborganellar localization of these proteins was predicted by MULocDeep. Conserved domains in these sequences were confirmed by CD-Search. These proteins were classified into 85 families on the basis of those conserved domains. A phylogenetic tree including pearl millet proteins and their counterparts in Arabidopsis thaliana and rice was constructed for each of these families. Sequence motifs were identified by MEME for each of these families.

Deciphering trait associated morpho-physiological responses in pearlmillet hybrids and inbred lines under salt stress

Pearl millet is a staple food for more than 90 million people residing in highly vulnerable hot arid and semi-arid regions of Africa and Asia. These regions are more prone to detrimental effects of soil salinity on crop performance in terms of reduced biomass and crop yields. We investigated the physiological mechanisms of salt tolerance to irrigation induced salinity stress (EC_iw ~3, 6 & 9 dSm^-1) and their confounding effects on plant growth and yield in pearl millet inbred lines and hybrids. On average, nearly 30% reduction in above ground plant biomass was observed at EC_iw ~6 dSm^-1 which stretched to 56% at EC_iw ~9 dSm^-1 in comparison to best available water. With increasing salinity stress, the crop performance of test hybrids was better in comparison to inbred lines; exhibiting relatively higher stomatal conductance (gS; 16%), accumulated lower proline (Pro; -12%) and shoot Na⁺/K⁺(-31%), synthesized more protein (SP; 2%) and sugars (TSS; 32%) compensating in lower biomass (AGB; -22%) and grain yield (GY: -14%) reductions at highest salinity stress of EC_iw ~9 dSm^-1. Physiological traits modeling underpinning plant salt tolerance and adaptation mechanism illustrated the key role of 7 traits (AGB, Pro, SS, gS, SPAD, Pn, and SP) in hybrids and 8 traits (AGB, Pro, PH, Na⁺, K⁺, Na⁺/K⁺, SPAD, and gS) in inbred lines towards anticipated grain yield variations in salinity stressed pearl millet. Most importantly, the AGB alone, explained >91% of yield variation among evaluated hybrids and inbreed lines at EC_iw ~9 dSm^-1. Cumulatively, the better morpho-physiological adaptation and lesser yield reduction with increasing salinity stress in pearl millet hybrids (HHB 146, HHB 272, and HHB 234) and inbred lines (H77/833-2-202, ICMA 94555 and ICMA 843-22) substantially complemented in increased plant salt tolerance and yield stability over a broad range of salinity stress. The information generated herein will help address in deciphering the trait associated physiological alterations to irrigation induced salt stress, and developing potential hybrids in pearl millet using these parents with special characteristics.

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.

Pangenomic analysis identifies structural variation associated with heat tolerance in pearl millet

Pearl millet is an important cereal crop worldwide and shows superior heat tolerance. Here, we developed a graph-based pan-genome by assembling ten chromosomal genomes with one existing assembly adapted to different climates worldwide and captured 424,085 genomic structural variations (SVs). Comparative genomics and transcriptomics analyses revealed the expansion of the RWP-RK transcription factor family and the involvement of endoplasmic reticulum (ER)-related genes in heat tolerance. The overexpression of one RWP-RK gene led to enhanced plant heat tolerance and transactivated ER-related genes quickly, supporting the important roles of RWP-RK transcription factors and ER system in heat tolerance. Furthermore, we found that some SVs affected the gene expression associated with heat tolerance and SVs surrounding ER-related genes shaped adaptation to heat tolerance during domestication in the population. Our study provides a comprehensive genomic resource revealing insights into heat tolerance and laying a foundation for generating more robust crops under the changing climate.

Genome-Wide Identification of Sweet Orange WRKY Transcription Factors and Analysis of Their Expression in Response to Infection by Penicillium digitatum

WRKY transcription factors (TFs) play a vital role in plant stress signal transduction and regulate the expression of various stress resistance genes. Sweet orange (Citrus sinensis) accounts for a large proportion of the world's citrus industry, which has high economic value, while Penicillium digitatum is a prime pathogenic causing postharvest rot of oranges. There are few reports on how CsWRKY TFs play their regulatory roles after P. digitatum infects the fruit. In this study, we performed genome-wide identification, classification, phylogenetic and conserved domain analysis of CsWRKY TFs, visualized the structure and chromosomal localization of the encoded genes, explored the expression pattern of each CsWRKY gene under P. digitatum stress by transcriptome data, and made the functional prediction of the related genes. This study provided insight into the characteristics of 47 CsWRKY TFs, which were divided into three subfamilies and eight subgroups. TFs coding genes were unevenly distributed on nine chromosomes. The visualized results of the intron-exon structure and domain are closely related to phylogeny, and widely distributed cis-regulatory elements on each gene played a global regulatory role in gene expression. The expansion of the CSWRKY TFs family was probably facilitated by twenty-one pairs of duplicated genes, and the results of Ka/Ks calculations indicated that this gene family was primarily subjected to purifying selection during evolution. Our transcriptome data showed that 95.7% of WRKY genes were involved in the transcriptional regulation of sweet orange in response to P. digitatum infection. We obtained 15 differentially expressed genes and used the reported function of AtWRKY genes as references. They may be involved in defense against P. digitatum and other pathogens, closely related to the stress responses during plant growth and development. Two interesting genes, CsWRKY2 and CsWRKY14, were expressed more than 60 times and could be used as excellent candidate genes in sweet orange genetic improvement. This study offers a theoretical basis for the response of CSWRKY TFs to P. digitatum infection and provides a vital reference for molecular breeding.

Genome-Wide Identification and Transcriptional Analysis of the MYB Gene Family in Pearl Millet (Pennisetum glaucum)

The MYB gene family widely exists in the plant kingdom and participates in the regulation of plant development and stress response. Pearl millet (Pennisetum glaucum (L.) R. Br.), as one of the most important cereals, is not only considered a good source of protein and nutrients but also has excellent tolerances to various abiotic stresses (e.g., salinity, water deficit, etc.). Although the genome sequence of pearl millet was recently published, bioinformatics and expression pattern analysis of the MYB gene family are limited. Here, we identified 208 PgMYB genes in the pearl millet genome and employed 193 high-confidence candidates for downstream analysis. Phylogenetic and structural analysis classified these PgMYBs into four subgroups. Eighteen pairs of segmental duplications of the PgMYB gene were found using synteny analysis. Collinear analysis revealed pearl millet had the closest evolutionary relationship with foxtail millet. Nucleotide substitution analysis (Ka/Ks) revealed PgMYB genes were under purifying positive selection pressure. Reverse transcription-quantitative PCR analysis of eleven R2R3-type PgMYB genes revealed they were preferentially expressed in shoots and seeds and actively responded to various environment stimuli. Current results provide insightful information regarding the molecular features of the MYB family in pearl millet to support further functional characterizations.

MYB Transcription Factor Family in Pearl Millet: Genome-Wide Identification, Evolutionary Progression and Expression Analysis under Abiotic Stress and Phytohormone Treatments

Transcription factors (TFs) are the regulatory proteins that act as molecular switches in controlling stress-responsive gene expression. Among them, the MYB transcription factor family is one of the largest TF family in plants, playing a significant role in plant growth, development, phytohormone signaling and stress-responsive processes. Pearl millet (Pennisetum glaucum L.) is one of the most important C4 crop plants of the arid and semi-arid regions of Africa and Southeast Asia for sustaining food and fodder production. To explore the evolutionary mechanism and functional diversity of the MYB family in pearl millet, we conducted a comprehensive genome-wide survey and identified 279 MYB TFs (PgMYB) in pearl millet, distributed unevenly across seven chromosomes of pearl millet. A phylogenetic analysis of the identified PgMYBs classified them into 18 subgroups, and members of the same group showed a similar gene structure and conserved motif/s pattern. Further, duplication events were identified in pearl millet that indicated towards evolutionary progression and expansion of the MYB family. Transcriptome data and relative expression analysis by qRT-PCR identified differentially expressed candidate PgMYBs (PgMYB2, PgMYB9, PgMYB88 and PgMYB151) under dehydration, salinity, heat stress and phytohormone (ABA, SA and MeJA) treatment. Taken together, this study provides valuable information for a prospective functional characterization of the MYB family members of pearl millet and their application in the genetic improvement of crop plants.

Physiological basis and differentially expressed genes in the salt tolerance mechanism of Thalassia hemprichii

Seagrass plays a vital role in the stability of marine ecology. The human development of marine resources has greatly affected the survival of seagrass. Seawater salinity is one of the important factors affecting its survival. Seagrass can survive in high saline environments for a long time and has evolved a variety of effective tolerance mechanisms. However, little is known about the molecular mechanisms underlying salinity tolerance by seagrass. Thalassia hemprichii is a seagrass species with a global distribution. It is also an ecologically important plant species in coastal waters. Nevertheless, the continuous environmental deterioration has gradually reduced the ecological niche of seagrasses. In this study, experiments were conducted to examine the effects of salinity changes on T. hemprichii. The result showed that the optimal salinity for T. hemprichii is 25 to 35 PSU. Although it can survive under high and low salinity, high mortality rates are common in such environments. Further analyses revealed that high salinity induces growth and developmental retardation in T. hemprichii and further causes yellowing. The parenchyma cells in T. hemprichii also collapse, the structure changes, soluble sugar accumulates rapidly, soluble proteins accumulate rapidly, the malondialdehyde (MDA) content reduces, and lipid peroxidation reduces in plant membranes. The molecular mechanisms of salt tolerance differ significantly between marine and terrestrial plants. We found 319 differentially expressed genes (DEGs). These genes regulate transport and metabolism, promoting environmental adaptation. The expression of these genes changed rapidly upon exposure of T. hemprichii to salinity stress for three hours. This is the first report on the physiological and biochemical changes and gene expression regulation of T. hemprichii under different salinity conditions. The findings of this study well deepen our understanding of T. hemprichii adaptations to changes in the shoal living environment.

WRKY transcription factors (TFs): Molecular switches to regulate drought, temperature, and salinity stresses in plants

The WRKY transcription factor (TF) belongs to one of the major plant protein superfamilies. The WRKY TF gene family plays an important role in the regulation of transcriptional reprogramming associated with plant stress responses. Change in the expression patterns of WRKY genes or the modifications in their action; participate in the elaboration of numerous signaling pathways and regulatory networks. WRKY proteins contribute to plant growth, for example, gamete formation, seed germination, post-germination growth, stem elongation, root hair growth, leaf senescence, flowering time, and plant height. Moreover, they play a key role in many types of environmental signals, including drought, temperature, salinity, cold, and biotic stresses. This review summarizes the current progress made in unraveling the functions of numerous WRKY TFs under drought, salinity, temperature, and cold stresses as well as their role in plant growth and development.

De novo transcriptome profiling unveils the regulation of phenylpropanoid biosynthesis in unripe Piper nigrum berries

BACKGROUND

Black pepper (Piper nigrum L.) is rich in bioactive compounds that make it an imperative constituent in traditional medicines. Although the unripe fruits have long been used in different Ayurvedic formulations, the mechanism of gene regulation resulting in the production of the bioactive compounds in black pepper is not much investigated. Exploring the regulatory factors favouring the production of bioactive compounds ultimately help to accumulate the medicinally important content of black pepper. The factors that enhance the biosynthesis of these compounds could be potential candidates for metabolic engineering strategies to obtain a high level production of significant biomolecules.

RESULTS

Being a non-model plant, de novo sequencing technology was used to unravel comprehensive information about the genes and transcription factors that are expressed in mature unripe green berries of P. nigrum from which commercially available black pepper is prepared. In this study, the key gene regulations involved in the synthesis of bioactive principles in black pepper was brought out with a focus on the highly expressed phenylpropanoid pathway genes. Quantitative real-time PCR analysis of critical genes and transcription factors in the different developmental stages from bud to the mature green berries provides important information useful for choosing the developmental stage that would be best for the production of a particular bioactive compound. Comparison with a previous study has also been included to understand the relative position of the results obtained from this study.

CONCLUSIONS

The current study uncovered significant information regarding the gene expression and regulation responsible for the bioactivity of black pepper. The key transcription factors and enzymes analyzed in this study are promising targets for achieving a high level production of significant biomolecules through metabolic engineering.

Genome-Wide Identification of WRKY Gene Family in Pitaya Reveals the Involvement of HmoWRKY42 in Betalain Biosynthesis

The WRKY gene family is a plant-specific transcription factor (TF) that regulates many physiological processes and (a) biotic stress responses. Despite this, little is known about the molecular properties and roles of WRKY TFs in pitaya betalain biosynthesis. Here we report the identification of 70 WRKY in Hylocereus undatus, their gene structure, locations on each chromosome, systematic phylogenetic analysis, conserved motif analysis, and synteny of HuWRKY genes. HmoWRKY42 is a Group IIb WRKY protein and contains a coiled-coil motif, a WRKY domain and a C₂H₂ zinc-finger motif (CX₅CX₂₃HXH). Results from yeast one-hybrid and transient dual-luciferase assays showed that HmoWRKY42 was a transcriptional repressor and could repress HmocDOPA5GT1 expression by binding to its promoter. Yeast two-hybrid assays showed that HmoWRKY42 could interact with itself to form homodimers. Knocking out the coiled-coil motif of HmoWRKY42 prevented its self-interaction and prevented it from binding to the HmocDOPA5GT1 promoter. Knocking out the WRKY domain and C₂H₂ zinc-finger motif sequence of HmoWRKY42 also prevented it from binding to the HmocDOPA5GT1 promoter. The coiled-coil motif, the WRKY domain and the C₂H₂ zinc finger motif are key motifs for the binding of HmoWRKY42 to the HmocDOPA5GT1 promoter. HmoWRKY42 is localized in the nucleus and possesses trans-activation ability responsible for pitaya betalain biosynthesis by repressing the transcription of HmocDOPA5GT1. As far as we know, no reports are available on the role of HmoWRKY42 in pitaya betalain biosynthesis. The results provide an important foundation for future analyses of the regulation and functions of the HuWRKY gene family.

Characterization of the WRKY gene family reveals its contribution to the adaptability of almond (Prunus dulcis)

Background

WRKY (WRKY DNA-binding domain) transcription factors an important gene family that widely regulates plant resistance to biological and abiotic stresses, such as drought, salt and ion stresses. However, research on the WRKY family in almond has not yet been reported. Almond is an economically important fruit tree in Xinjiang that have strong resistance to various stresses.

Results

A total of 62 PdWRKY genes were identified (including six pairs of homologous genes), and the phylogenetic tree was divided into three groups according to the WRKY domain and zinc finger motifs. The members of each group had a significant number of conserved motifs and exons/introns distributed unevenly across eight chromosomes, as well as 24 pairs of fragment duplicates and nine pairs of tandem duplicates. Moreover, the synteny and Ka/Ks analyses of the WRKY genes among almond and distinct species provided more detailed evidence for PdWRKY genes evolution. The examination of different tissue expression patterns showed that PdWRKY genes have tissue-specific expression characteristics. The qRT-PCR results showed that PdWRKY genes participate in the resistance of almond to the effects of low-temperature, drought and salt stress and that the expression levels of these genes change over time, exhibiting spatiotemporal expression characteristics. It is worth noting that many genes play a significant role in low-temperature stress resistance. In addition, based on the conserved WRKY motif, 321 candidate target genes were identified as having functions in multiple pathways.

Conclusions

We conducted systematic bioinformatics analysis and abiotic stress research on the WRKY gene family in almond, laying the foundation for future PdWRKY genes research and improvements to almond production and breeding.

Genome-wide survey of the GATA gene family in camptothecin-producing plant Ophiorrhiza pumila

Background

Ophiorrhiza pumila (Rubiaceae) is capable of producing camptothecin (CPT), one monoterpene indole alkaloid extensively employed in the treatment of multiple cancers. Transcription factors (TFs) GATA are a group of transcription regulators involved in plant development and metabolism, and show the feature of binding to the GATA motif within the promoters of target genes. However, GATA TFs have not been characterized in O. pumila.

Result

In this study, a total of 18 GATA genes classified into four subfamilies were identified, which randomly distributed on 11 chromosomes of O. pumila. Synteny analysis of GATA genes between O. pumila and other plant species such as Arabidopsis thaliana, Oryza sativa, Glycine max, Solanum lycopersicum, Vitis vinifera, and Catharanthus roseus genomes were analyzed. Tissue expression pattern revealed that OpGATA1 and OpGATA18 were found to be correlated with ASA, MK, CPR and GPPS, which were highly expressed in leaves. OpGATA7, showed high expression in roots as most of the CPT biosynthetic pathway genes did, suggesting that these OpGATAs may be potential candidates regulating CPT biosynthesis in O. pumila.

Conclusions

In this study, we systematically analyzed the OpGATA TFs, and provided insights into the involvement of OpGATA TFs from O. pumila in CPT biosynthesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08484-x.

Identification of drought responsive Elaeis guineensis WRKY transcription factors with sensitivity to other abiotic stresses and hormone treatments

BACKGROUND

The ability of plants to withstand and thrive in an adverse environment is crucial to ensure their survivability and yield performance. The WRKY transcription factors (TFs) have crucial roles in plant growth, development and stress response, particularly drought stress. In oil palm, drought is recognized as one of the major yield limiting factors. However, the roles of WRKY TFs in the drought response of oil palm is unclear.

RESULTS

Herein, we studied the transcriptome of drought treated oil palm leaf and identified 40 differentially expressed genes (DEGs) of WRKY TFs, of which 32 DEGs were upregulated and 8 DEGs were downregulated in response to drought stress in oil palm. They were categorized into Groups I to IV based on the numbers of WRKY domain and the structural difference in the zinc finger domain. Multiple stress- and hormone-responsive cis-regulatory elements were detected in the drought responsive oil palm EgWRKY (Dro-EgWRKY) genes. Fourteen of the 15 selected oil palm WRKY (EgWRKY) genes demonstrated a tissue-specific expression profile except for EgWRKY28 (Group I), which was expressed in all tissues tested. The expression levels of 15 candidate EgWRKYs were upregulated upon salinity and heat treatments, while several genes were also inducible by abscisic acid, methyl jasmonate, salicylic acid and hydrogen peroxide treatments. Members of the Group III WRKY TFs including EgWRKY07, 26, 40, 52, 59, 73 and 81 displayed multiple roles in drought- and salinity-response under the modulation of phytohormones.

CONCLUSIONS

EgWRKY TFs of oil palm are involved in phytohormones and abiotic stress responses including drought, salinity and heat. EgWRKY07, 26, 59 and 81 from Group III maybe important regulators in modulating responses of different abiotic stresses. Further functional analysis is required to understand the underlying mechanism of WRKY TFs in the regulatory network of drought stress.

A Cys2His2 Zinc Finger Transcription Factor BpSZA1 Positively Modulates Salt Stress in Betula platyphylla

Zinc finger proteins (ZFPs) are widely involved in plant growth and abiotic stress responses, however, few of these proteins have been functionally characterized in tree species. In this study, we cloned and characterized the BpSZA1 gene encoding a C2H2-type ZFP from Betula platyphylla. BpSZA1 is a transcription factor localized in the nucleus, with a transcription activation domain located at the N-terminus. BpSZA1 was predominantly expressed in stems and was induced by salt. We generated transgenic birch lines displaying overexpression (OE) or RNAi silencing (Ri) of BpSZA1 and exposed these along with wild-type birch seedlings to salinity. Phenotypic and physiological parameters such as superoxide dismutase, peroxisome, H₂O₂ content, proline content, water loss rate, and malondialdehyde content were examined. Overexpression of BpSZA1 in birch conferred increased salt tolerance. Chromatin immunoprecipitation-qPCR and RNA-seq showed that BpSZA1 binds to the GAGA-motif in the promoter of downstream target genes including BpAPX1, BpAPX2, BpCAT, and Bp6PGDH to activate their transcription. BpSZA1 also participates in abscisic acid (ABA) biosynthesis, proline biosynthesis, and the ABA/jasmonic acid pathway to enhance the salt stress of B. platyphylla.

CaWRKY30 Positively Regulates Pepper Immunity by Targeting CaWRKY40 against Ralstonia solanacearum Inoculation through Modulating Defense-Related Genes

The WRKY transcription factors (TFs) network is composed of WRKY TFs’ subset, which performs a critical role in immunity regulation of plants. However, functions of WRKY TFs’ network remain unclear, particularly in non-model plants such as pepper (Capsicum annuum L.). This study functionally characterized CaWRKY30—a member of group III Pepper WRKY protein—for immunity of pepper against Ralstonia solanacearum infection. The CaWRKY30 was detected in nucleus, and its transcriptional expression levels were significantly upregulated by R. solanacearum inoculation (RSI), and foliar application ethylene (ET), abscisic acid (ABA), and salicylic acid (SA). Virus induced gene silencing (VIGS) of CaWRKY30 amplified pepper’s vulnerability to RSI. Additionally, the silencing of CaWRKY30 by VIGS compromised HR-like cell death triggered by RSI and downregulated defense-associated marker genes, like CaPR1, CaNPR1, CaDEF1, CaABR1, CaHIR1, and CaWRKY40. Conversely, transient over-expression of CaWRKY30 in pepper leaves instigated HR-like cell death and upregulated defense-related maker genes. Furthermore, transient over-expression of CaWRKY30 upregulated transcriptional levels of CaWRKY6, CaWRKY22, CaWRKY27, and CaWRKY40. On the other hand, transient over-expression of CaWRKY6, CaWRKY22, CaWRKY27, and CaWRKY40 upregulated transcriptional expression levels of CaWRKY30. The results recommend that newly characterized CaWRKY30 positively regulates pepper’s immunity against Ralstonia attack, which is governed by synergistically mediated signaling by phytohormones like ET, ABA, and SA, and transcriptionally assimilating into WRKY TFs networks, consisting of CaWRKY6, CaWRKY22, CaWRKY27, and CaWRKY40. Collectively, our data will facilitate to explicate the underlying mechanism of crosstalk between pepper’s immunity and response to RSI.

A Review of Recent Advances and Future Directions in the Management of Salinity Stress in Finger Millet

Salinity stress is a major environmental impediment affecting the growth and production of crops. Finger millet is an important cereal grown in many arid and semi-arid areas of the world characterized by erratic rainfall and scarcity of good-quality water. Finger millet salinity stress is caused by the accumulation of soluble salts due to irrigation without a proper drainage system, coupled with the underlying rocks having a high salt content, which leads to the salinization of arable land. This problem is projected to be exacerbated by climate change. The use of new and efficient strategies that provide stable salinity tolerance across a wide range of environments can guarantee sustainable production of finger millet in the future. In this review, we analyze the strategies that have been used for salinity stress management in finger millet production and discuss potential future directions toward the development of salt-tolerant finger millet varieties. This review also describes how advanced biotechnological tools are being used to develop salt-tolerant plants. The biotechnological techniques discussed in this review are simple to implement, have design flexibility, low cost, and highly efficient. This information provides insights into enhancing finger millet salinity tolerance and improving production.

Comprehensive identification and expression analysis of GRAS gene family under abiotic stress and phytohormone treatments in Pearl millet

Pearl millet is an important C4 cereal plant that possesses enormous capacity to survive under extreme climatic conditions. It serves as a major food source for people in arid and semiarid regions of south-east Asia and Africa. GRAS is an important transcription factor gene family of plant that play a critical role in regulating developmental processes, stress responses and phytohormonal signalling. In the present study, we have identified a total number of 57 GRAS members in pearl millet. Phylogenetic analysis clustered all the PgGRAS genes into eight groups (GroupI-GroupVIII). Motif analysis has shown that all the PgGRAS proteins had conserved GRAS domains and gene structure analysis revealed a high structural diversity among PgGRAS genes. Expression patterns of PgGRAS genes in different tissues (leaf, stem and root) and under various abiotic stress (drought, heat and salinity) were determined. Further, expression analysis was also carried out in response to various hormones (SA, MeJA, GA and ABA). The results provide a clear understanding of GRAS transcription factor family in pearl millet, and lay a good foundation for the functional characterisation of GRAS genes in pearl millet.

WRKY transcription factors and plant defense responses: latest discoveries and future prospects

WRKY transcription factors are among the largest families of transcriptional regulators. In this review, their pivotal role in modulating various signal transduction pathways during biotic and abiotic stresses is discussed. Transcription factors (TFs) are important constituents of plant signaling pathways that define plant responses against biotic and abiotic stimuli besides playing a role in response to internal signals which coordinate different interacting partners during developmental processes. WRKY TFs, deriving their nomenclature from their signature DNA-binding sequence, represent one of the largest families of transcriptional regulators found exclusively in plants. By modulating different signal transduction pathways, these TFs contribute to various plant processes including nutrient deprivation, embryogenesis, seed and trichome development, senescence as well as other developmental and hormone-regulated processes. A growing body of research suggests transcriptional regulation of WRKY TFs in adapting plant to a variety of stressed environments. WRKY TFs can regulate diverse biological functions from receptors for pathogen triggered immunity, modulator of chromatin for specific interaction and signal transfer through a complicated network of genes. Latest discoveries illustrate the interaction of WRKY proteins with other TFs to form an integral part of signaling webs that regulate several seemingly disparate processes and defense-related genes, thus establishing their significant contributions to plant immune response. The present review starts with a brief description on the structural characteristics of WRKY TFs followed by the sections that present recent evidence on their roles in diverse biological processes in plants. We provide a comprehensive overview on regulatory crosstalks involving WRKY TFs during multiple stress responses in plants and future prospects of WRKY TFs as promising molecular diagnostics for enhancing crop improvement.

Plant Transcription Factors Involved in Drought and Associated Stresses

Transcription factors (TFs) play a significant role in signal transduction networks spanning the perception of a stress signal and the expression of corresponding stress-responsive genes. TFs are multi-functional proteins that may simultaneously control numerous pathways during stresses in plants-this makes them powerful tools for the manipulation of regulatory and stress-responsive pathways. In recent years, the structure-function relationships of numerous plant TFs involved in drought and associated stresses have been defined, which prompted devising practical strategies for engineering plants with enhanced stress tolerance. Vast data have emerged on purposely basic leucine zipper (bZIP), WRKY, homeodomain-leucine zipper (HD-Zip), myeloblastoma (MYB), drought-response elements binding proteins/C-repeat binding factor (DREB/CBF), shine (SHN), and wax production-like (WXPL) TFs that reflect the understanding of their 3D structure and how the structure relates to function. Consequently, this information is useful in the tailored design of variant TFs that enhances our understanding of their functional states, such as oligomerization, post-translational modification patterns, protein-protein interactions, and their abilities to recognize downstream target DNA sequences. Here, we report on the progress of TFs based on their interaction pathway participation in stress-responsive networks, and pinpoint strategies and applications for crops and the impact of these strategies for improving plant stress tolerance.

TGIF-DB: terse genomics interface for developing botany

Objectives

Pearl millet (Pennisetum glaucum) is a staple cereal crop for semi-arid regions. Its whole genome sequence and deduced putative gene sequences are available. However, the functions of many pearl millet genes are unknown. Situations are similar for other crop species such as garden asparagus (Asparagus officinalis), chickpea (Cicer arietinum) and Tartary buckwheat (Fagopyrum tataricum). The objective of the data presented here was to improve functional annotations of genes of pearl millet, garden asparagus, chickpea and Tartary buckwheat with gene annotations of model plants, to systematically provide such annotations as well as their sequences on a website, and thereby to promote genomics for those crops.

Data description

Sequences of genomes and transcripts of pearl millet, garden asparagus, chickpea and Tartary buckwheat were downloaded from a public database. These transcripts were associated with functional annotations of their Arabidopsis thaliana and rice (Oryza sativa) counterparts identified by BLASTX. Conserved domains in protein sequences of those species were identified by the HMMER scan with the Pfam database. The resulting data was deposited in the figshare repository and can be browsed on the Terse Genomics Interface for Developing Botany (TGIF-DB) website (http://webpark2116.sakura.ne.jp/rlgpr/).

Transcriptome Analysis Reveals Genes of Flooding-Tolerant and Flooding-Sensitive Rapeseeds Differentially Respond to Flooding at the Germination Stage

Flooding results in significant crop yield losses due to exposure of plants to hypoxic stress. Various studies have reported the effect of flooding stress at seedling establishment or later stages. However, the molecular mechanism prevailing at the germination stage under flooding stress remains enigmatic. The present study highlights the comparative transcriptome analysis in two rapeseed lines, i.e., flooding-tolerant (Santana) and -sensitive (23651) lines under control and 6-h flooding treatments at the germination stage. A total of 1840 up-regulated and 1301 down-regulated genes were shared by both lines in response to flooding. There were 4410 differentially expressed genes (DEGs) with increased expression and 4271 DEGs with reduced expression shared in both control and flooding conditions. Gene ontology (GO) enrichment analysis revealed that “transcription regulation”, “structural constituent of cell wall”, “reactive oxygen species metabolic”, “peroxidase”, oxidoreductase”, and “antioxidant activity” were the common processes in rapeseed flooding response. In addition, the processes such as “hormone-mediated signaling pathway”, “response to organic substance response”, “motor activity”, and “microtubule-based process” are likely to confer rapeseed flooding resistance. Mclust analysis clustered DEGs into nine modules; genes in each module shared similar expression patterns and many of these genes overlapped with the top 20 DEGs in some groups. This work provides a comprehensive insight into gene responses and the regulatory network in rapeseed flooding stress and provides guidelines for probing the underlying molecular mechanisms in flooding resistance.

Biotechnological approaches to dissect climate-resilient traits in millets and their application in crop improvement

'Small millets' is a generic term that includes all the millets except pearl millet and sorghum. These small or minor millets constitute eleven species that are marginally cultivated and consumed worldwide. These small millets possess excellent agronomic-, climate-resilient, and nutritional traits, although they lack popularity. Small millets withstand a broad spectrum of environmental stresses and possess better water-use and nitrogen-use efficiencies. Of note, small millets are five- to seven-fold nutritionally rich in terms of protein, bioactive compounds, micro- and macro-nutrients as compared to major cereals. Irrespective of these merits, small millets have received little research attention compared to major millets and cereals. However, the knowledge generated from such studies is significant for the improvement of millets per se and for translating the information to improve major cereals through breeding and transgene-based approaches. Given this, the review enumerates the efforts invested in dissecting the climate-resilient traits in small millets and provides a roadmap for deploying the information in crop improvement of millets as well as cereals in the scenario of climate change.

De-novo transcriptome analysis unveils differentially expressed genes regulating drought and salt stress response in Panicum sumatrense

Screening the transcriptome of drought tolerant variety of little millet (Panicum sumatrense), a marginally cultivated, nutritionally rich, susbsistent crop, can identify genes responsible for its hardiness and enable identification of new sources of genetic variation which can be used for crop improvement. RNA-Seq generated ~ 230 million reads from control and treated tissues, which were assembled into 86,614 unigenes. In silico differential gene expression analysis created an overview of patterns of gene expression during exposure to drought and salt stress. Separate gene expression profiles for leaf and root tissue revealed the differences in regulatory mechanisms operating in these tissues during exposure to abiotic stress. Several transcription factors were identified and studied for differential expression. 61 differentially expressed genes were found to be common to both tissues under drought and salinity stress and were further validated using qRT-PCR. Transcriptome of P. sumatrense was also used to mine for genic SSR markers relevant to abiotic stress tolerance. This study is first report on a detailed analysis of molecular mechanisms of drought and salinity stress tolerance in a little millet variety. Resources generated in this study can be used as potential candidates for further characterization and to improve abiotic stress tolerance in food crops.

Function and Mechanism of WRKY Transcription Factors in Abiotic Stress Responses of Plants

The WRKY gene family is a plant-specific transcription factor (TF) group, playing important roles in many different response pathways of diverse abiotic stresses (drought, saline, alkali, temperature, and ultraviolet radiation, and so forth). In recent years, many studies have explored the role and mechanism of WRKY family members from model plants to agricultural crops and other species. Abiotic stress adversely affects the growth and development of plants. Thus, a review of WRKY with stress responses is important to increase our understanding of abiotic stress responses in plants. Here, we summarize the structural characteristics and regulatory mechanism of WRKY transcription factors and their responses to abiotic stress. We also discuss current issues and future perspectives of WRKY transcription factor research.

WRKY Transcription Factors in Medicago sativa L.: Genome-Wide Identification and Expression Analysis Under Abiotic Stress

Alfalfa (Medicago sativa L.) is the most widely cultivated leguminous herb in the world. Its agricultural development has been restricted by various adverse environmental conditions, including water deficiency, high salinity, and low temperature. WRKY transcription factors (TFs) serve important roles in the regulation of plant development and stress responses. Research on the WRKY gene family has been reported for several species, but minimal information is available for alfalfa. In the present study, a total of 107 WRKY genes were identified in alfalfa and divided into 3 main groups. The classification, evolution, conserved motifs, and tissue expression were comprehensively analyzed. Meanwhile, 27 MsWRKY candidate genes that may be involved in abiotic stress were isolated through an analysis of gene expression profiles under different stresses, including cold, abscisic acid, drought, and salt treatments. Additionally, investigation of the cis-elements and potential biological functions of these genes further revealed that MsWRKY TFs may serve important roles in multiple stress resistance in alfalfa. This study provides an important foundation for future cloning and functional studies of WRKY genes in alfalfa.

Genome-wide Identification of WRKY transcription factor family members in sorghum (Sorghum bicolor (L.) moench)

WRKY transcription factors regulate diverse biological processes in plants, including abiotic and biotic stress responses, and constitute one of the largest transcription factor families in higher plants. Although the past decade has seen significant progress towards identifying and functionally characterizing WRKY genes in diverse species, little is known about the WRKY family in sorghum (Sorghum bicolor (L.) moench). Here we report the comprehensive identification of 94 putative WRKY transcription factors (SbWRKYs). The SbWRKYs were divided into three groups (I, II, and III), with those in group II further classified into five subgroups (IIa–IIe), based on their conserved domains and zinc finger motif types. WRKYs from the model plant Arabidopsis (Arabidopsis thaliana) were used for the phylogenetic analysis of all SbWRKY genes. Motif analysis showed that all SbWRKYs contained either one or two WRKY domains and that SbWRKYs within the same group had similar motif compositions. SbWRKY genes were located on all 10 sorghum chromosomes, and some gene clusters and two tandem duplications were detected. SbWRKY gene structure analysis showed that they contained 0–7 introns, with most SbWRKY genes consisting of two introns and three exons. Gene ontology (GO) annotation functionally categorized SbWRKYs under cellular components, molecular functions and biological processes. A cis-element analysis showed that all SbWRKYs contain at least one stress response-related cis-element. We exploited publicly available microarray datasets to analyze the expression profiles of 78 SbWRKY genes at different growth stages and in different tissues. The induction of SbWRKYs by different abiotic stresses hinted at their potential involvement in stress responses. qRT-PCR analysis revealed different expression patterns for SbWRKYs during drought stress. Functionally characterized WRKY genes in Arabidopsis and other species will provide clues for the functional characterization of putative orthologs in sorghum. Thus, the present study delivers a solid foundation for future functional studies of SbWRKY genes and their roles in the response to critical stresses such as drought.