Wheat transcription factor TaWRKY70 is positively involved in high-temperature seedling plant resistance to Puccinia striiformis f. sp. tritici

TaWRKY50-TaSARK7 module-mediated cysteine-rich protein phosphorylation suppresses the programmed cell death response to Chinese wheat mosaic virus infection

WRKY transcription factors are widely involved in plant responses to biotic and abiotic stresses. However, there is currently a limited understanding of the regulation of viral infection by WRKY transcription factors in wheat (Triticum aestivum). The WRKY transcription factor TaWRKY50 in group IIb wheat exhibited a significant response to Chinese wheat mosaic virus infection. TaWRKY50 is localized in the nucleus and is an activating transcription factor. Interestingly, we found that silencing TaWRKY50 induces cell death following inoculation with CWMV. The protein kinase TaSAPK7 is specific to plants, whereas NbSRK is a closely related kinase with high homology to TaSAPK7. The transcriptional activities of both TaSAPK7 and NbSRK can be enhanced by TaWRKY50 binding to their promoters. CRP is an RNA silencing suppressor. Furthermore, TaWRKY50 may regulate CWMV infection by regulating the expression of TaSAPK7 and NbSRK to increase CRP phosphorylation and reduce the amount of programmed cell death (PCD).

Genome-wide analysis of salicylic acid and jasmonic acid signalling marker gene families in wheat

Jasmonic acid (JA) and salicylic acid (SA) phytohormone pathways are important regulators of stress tolerance. Knowledge regarding the diversity, phylogeny and functionality of wheat genes involved in JA and SA response is limited. Using Arabidopsis, rice and wheat genomic and wheat disease transcriptomic data, we deduced the size, phylogenetic diversity and pathogen-responsiveness of seven hormone-responsive gene families, and thus selected 14 candidates as potential hormone responsive gene markers. Gene-specific expression studies assessed the impact of exogenous JA and SA on their transcriptional activation in leaves of two distinct wheat cultivars. RNAseq data were interrogated to assess their disease responsiveness and tissue-specific expression. This study elucidated the number, phylogeny and pathogen-responsiveness of wheat genes from seven families, including 12 TaAOS, 6 TaJAMyb, 256 TaWRKY group III, 85 TaPR1, 205 TaPR2, 76 TaPR3 and 124 TaPR5. This included the first description of the wheat AOS, JAMyb, PR2, PR3 and PR5 gene families. Gene expression studies delineated TaAOS1-5B and TaJAMyb-4A as JA-responsive in leaves, but not significantly responsive to SA treatment, while TaWRKY45-B was a SA- but not a JA-responsive marker. Other candidate genes were either unresponsive or non-specific to SA or JA. Our findings highlight that all seven gene families are greatly expanded in wheat as compared to other plants (up to 7.6-fold expansion), and demonstrate disparity in the response to biotic stress between some homoeologous and paralogous sequences within these families. The SA- and JA-responsive marker genes identified herein will prove useful tools to monitor these signalling pathways in wheat.

Decoding the molecular mechanism underlying salicylic acid (SA)-mediated plant immunity: an integrated overview from its biosynthesis to the mode of action

Salicylic acid (SA) is an important phytohormone, well-known for its regulatory role in shaping plant immune responses. In recent years, significant progress has been made in unravelling the molecular mechanisms underlying SA biosynthesis, perception, and downstream signalling cascades. Through the concerted efforts employing genetic, biochemical, and omics approaches, our understanding of SA-mediated defence responses has undergone remarkable expansion. In general, following SA biosynthesis through Avr effectors of the pathogens, newly synthesized SA undergoes various biochemical changes to achieve its active/inactive forms (e.g. methyl salicylate). The activated SA subsequently triggers signalling pathways associated with the perception of pathogen-derived signals, expression of defence genes, and induction of systemic acquired resistance (SAR) to tailor the intricate regulatory networks that coordinate plant immune responses. Nonetheless, the mechanistic understanding of SA-mediated plant immune regulation is currently limited because of its crosstalk with other signalling networks, which makes understanding this hormone signalling more challenging. This comprehensive review aims to provide an integrated overview of SA-mediated plant immunity, deriving current knowledge from diverse research outcomes. Through the integration of case studies, experimental evidence, and emerging trends, this review offers insights into the regulatory mechanisms governing SA-mediated immunity and signalling. Additionally, this review discusses the potential applications of SA-mediated defence strategies in crop improvement, disease management, and sustainable agricultural practices.

TaCRT3 Is a Positive Regulator of Resistance to Blumeria graminis f. sp. tritici in Wheat

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most prevalent diseases of wheat worldwide and can lead to severe yield reductions. Identifying genes involved in powdery mildew resistance will be useful for disease resistance breeding and control. Calreticulin (CRT) is a member of multigene family widely found in higher plants and is associated with a variety of plant physiological functions and defense responses. However, the role of CRT in wheat resistance to powdery mildew remains unclear. TaCRT3 was identified from the proteomic sequence of an incompatible interaction between the wheat (Triticum aestivum) cultivar Xingmin 318 and the Bgt isolate E09. Following analysis of transient expression of the GFP-TaCRT3 fusion protein in Nicotiana benthamiana leaves, TaCRT3 was localized in the nucleus, cytoplasm, and cell membrane. Transcript expression levels of TaCRT3 were significantly upregulated in the wheat-Bgt incompatible interaction. More critically, knockdown of TaCRT3 using virus-induced gene silencing resulted in attenuated resistance to Bgt in wheat. Histological analysis showed a significant increase in Bgt development in TaCRT3-silenced plants, whereas the pathogen-related gene was significantly downregulated in TaCRT3-silenced leaves. In addition, overexpression of TaCRT3 in wheat enhanced the resistance to powdery mildew, the growth of Bgt was significantly inhibited, and the area of H2O2 near the infection site and the expression of defense-related genes of the salicylic acid pathway significantly increased. These findings imply that TaCRT3 may act as a disease resistance factor that positively regulates resistance to powdery mildew, during which SA signaling is probably activated.

Genome-wide identification, structural characterization and gene expression analysis of the WRKY transcription factor family in pea (Pisum sativum L.)

BACKGROUND

The WRKY gene family is one of the largest families of transcription factors in higher plants, and WRKY transcription factors play important roles in plant growth and development as well as in response to abiotic stresses; however, the WRKY gene family in pea has not been systematically reported.

RESULTS

In this study, 89 pea WRKY genes were identified and named according to the random distribution of PsWRKY genes on seven chromosomes. The gene family was found to have nine pairs of tandem duplicates and 19 pairs of segment duplicates. Phylogenetic analyses of the PsWRKY and 60 Arabidopsis WRKY proteins were performed to determine their homology, and the PsWRKYs were classified into seven subfamilies. Analysis of the physicochemical properties, motif composition, and gene structure of pea WRKYs revealed significant differences in the physicochemical properties within the PsWRKY family; however, their gene structure and protein-conserved motifs were highly conserved among the subfamilies. To further investigate the evolutionary relationships of the PsWRKY family, we constructed comparative syntenic maps of pea with representative monocotyledonous and dicotyledonous plants and found that it was most recently homologous to the dicotyledonous WRKY gene families. Cis-acting element analysis of PsWRKY genes revealed that this gene family can respond to hormones, such as abscisic acid (ABA), indole-3-acetic acid (IAA), gibberellin (GA), methyl jasmonate (MeJA), and salicylic acid (SA). Further analysis of the expression of 14 PsWRKY genes from different subfamilies in different tissues and fruit developmental stages, as well as under five different hormone treatments, revealed differences in their expression patterns in the different tissues and fruit developmental stages, as well as under hormone treatments, suggesting that PsWRKY genes may have different physiological functions and respond to hormones.

CONCLUSIONS

In this study, we systematically identified WRKY genes in pea for the first time and further investigated their physicochemical properties, evolution, and expression patterns, providing a theoretical basis for future studies on the functional characterization of pea WRKY genes during plant growth and development.

Ethylene enhances resistance to cucumber green mottle mosaic virus via the ClWRKY70-ClACO5 module in watermelon plants

Introduction

Ethylene (ET) is involved in plant responses to viral infection. However, its molecular mechanisms and regulatory network remain largely unknown.

Methods and results

In the present study, we report that cucumber green mottle mosaic virus (CGMMV) in watermelon (Citrullus lanatus) triggers ET production by inducing the expression of ClACO5, a key gene of the ET biosynthesis pathway through transcriptome data analysis and gene function validation. The knock-down of ClACO5 expression through virus-induced gene silencing in watermelon and overexpressing ClACO5 in transgenic Nicotiana benthamiana indicated that ClACO5 positively regulates CGMMV resistance and ET biosynthesis. The salicylic acid-responsive transcription factor gene ClWRKY70 shares a similar expression pattern with ClACO5. We demonstrate that ClWRKY70 directly binds to the W-box cis-element in the ClACO5 promoter and enhances its transcription. In addition, ClWRKY70 enhances plant responses to CGMMV infection by regulating ClACO5 expression in watermelon.

Discussion

Our results demonstrate that the ClWRKY70-ClACO5 module positively regulates resistance to CGMMV infection in watermelon, shedding new light on the molecular basis of ET accumulation in watermelon in response to CGMMV infection.

The interaction of two Puccinia striiformis f. sp. tritici effectors modulates high-temperature seedling-plant resistance in wheat

Wheat cultivar Xiaoyan 6 (XY6) has high-temperature seedling-plant (HTSP) resistance to Puccinia striiformis f. sp. tritici (Pst). However, the molecular mechanism of Pst effectors involved in HTSP resistance remains unclear. In this study, we determined the interaction between two Pst effectors, PstCEP1 and PSTG_11208, through yeast two-hybrid (Y2H), bimolecular fluorescence complementation (BiFC), and pull-down assays. Transient overexpression of PSTG_11208 enhanced HTSP resistance in different temperature treatments. The interaction between PstCEP1 and PSTG_11208 inhibited the resistance enhancement by PSTG_11208. Furthermore, the wheat apoplastic thaumatin-like protein 1 (TaTLP1) appeared to recognize Pst invasion by interacting with PSTG_11208 and initiate the downstream defence response by the pathogenesis-related protein TaPR1. Silencing of TaTLP1 and TaPR1 separately or simultaneously reduced HTSP resistance to Pst in XY6. Moreover, we found that PstCEP1 targeted wheat ferredoxin 1 (TaFd1), a homologous protein of rice OsFd1. Silencing of TaFd1 affected the stability of photosynthesis in wheat plants, resulting in chlorosis on the leaves and reducing HTSP resistance. Our findings revealed the synergistic mechanism of effector proteins in the process of pathogen infection.

WRKY Transcriptional Factor IlWRKY70 from Iris laevigata Enhances Drought and Salinity Tolerances in Nicotiana tabacum

Drought and high salinity greatly affect plant growth and development. WRKY transcription factors play a key role in plant tolerance to abiotic stress, but the functions of WRKYs in the ornamental monocotyledon Iris laevigata remain largely unexplored. In this study, we cloned IlWRKY70 and found that it is a Group III WRKY localized in the nucleus. The expression of IlWRKY70 was induced by NaCl and PEG-6000, which reached peaks (4.38 and 5.65 times) after 3 h and 1 h, respectively. The exogenous overexpression of IlWRKY70 in N. tabacum significantly improved the resistance under NaCl and drought treatments, as evidenced by higher germination rates, longer root lengths, and increased fresh weights compared to those of control plants. In addition, transgenic seedlings showed significantly reduced wilting, higher photosynthetic performance, higher Fv/Fm and chlorophyll content, and lower stomatal conductance. Moreover, transgenic lines showed higher antioxidant enzymatic activities, lower reactive oxygen species (ROS), and lower malondialdehyde contents. Accordingly, we also found higher expressions of antioxidant defense genes, including SOD, CAT, and POD, in transgenic lines compared to controls under salt and drought stresses. Thus, IlWRKY70 enhances the abilities of salt and drought tolerances in plants, at least partially, via ROS regulation and can be used for breeding I. laevigata possessing enhanced salt and drought resistances.

Comparative Transcriptomic Analysis of Wheat Cultivars in Response to Xanthomonas translucens pv. cerealis and Its T2SS, T3SS, and TALEs Deficient Strains

Xanthomonas translucens pv. cerealis causes bacterial leaf streak disease on small grain cereals. Type II and III secretion systems (T2SS and T3SS) play a pivotal role in the pathogenicity of the bacterium, while no data are available on the transcriptomic profile of wheat cultivars infected with either wild type (WT) or mutants of the pathogen. In this study, WT, TAL-effector mutants, and T2SS/T3SS mutants of X. translucens pv. cerealis strain NXtc01 were evaluated for their effect on the transcriptomic profile of two wheat cultivars, 'Chinese Spring' and 'Yangmai-158', using Illumina RNA-sequencing technology. RNA-Seq data showed that the number of differentially expressed genes (DEGs) was higher in Yangmai-158 than in Chinese Spring, suggesting higher susceptibility of Yangmai-158 to the pathogen. In T2SS, most suppressed DEGs were related to transferase, synthase, oxidase, WRKY, and bHLH transcription factors. The gspD mutants showed significantly decreased disease development in wheat, suggesting an active contribution of T2SS in virulence. Moreover, the gspD mutant restored full virulence and its multiplication in planta by addition of gspD in trans. In the T3SS-deficient strain, downregulated DEGs were associated with cytochrome, peroxidases, kinases, phosphatases, WRKY, and ethylene-responsive transcription factors. In contrast, upregulated DEGs were trypsin inhibitors, cell number regulators, and calcium transporter. Transcriptomic analyses coupled with quantitative real-time-PCR indicated that some genes are upregulated in Δtal1/Δtal2 compared with the tal-free strain, but no direct interaction was observed. These results provide novel insight into wheat transcriptomes in response to X. translucens infection and pave the way for understanding host-pathogen interactions.

The Leucine-Rich Repeat Receptor-Like Kinase Protein TaSERK1 Positively Regulates High-Temperature Seedling Plant Resistance to Puccinia striiformis f. sp. tritici by Interacting with TaDJA7

Somatic embryogenesis receptor kinases (SERKs) belong to the leucine-rich repeat receptor-like kinase (LRR-RLK) subfamily, and many LRR-RLKs have been proven to play a key role in plant immune signal transmission. However, the functions of SERKs in resistance to stripe rust caused by Puccinia striiformis f. sp. tritici remains unknown. Here, we identified a gene, TaSERK1, from Xiaoyan 6, a wheat cultivar possessing high-temperature seedling-plant (HTSP) resistance to the fungal pathogen P. striiformis f. sp. tritici and expresses its resistance at the seedling stage. The expression level of TaSERK1 was upregulated upon P. striiformis f. sp. tritici inoculation under relatively high temperatures. The transcriptional level of TaSERK1 was significantly increased under exogenous salicylic acid and brassinosteroids treatments. The barley stripe mosaic virus-induced gene silencing assay indicated that TaSERK1 positively regulated the HTSP resistance to stripe rust. The transient expression of TaSERK1 in tobacco leaves confirmed its subcellular localization on the plasma membrane. Furthermore, TaSERK1 interacted with and phosphorylated the chaperone protein TaDJA7, which belongs to the heat shock protein 40 subfamily. Silencing TaDJA7 compromised the HTSP resistance to stripe rust. The results indicated that when the membrane immune receptor TaSERK1 perceives the P. striiformis f. sp. tritici infection under relatively high temperatures, it transmits the signal to TaDJA7 to activate HTSP resistance to the pathogen.

Comparative transcriptome profiling of near isogenic lines PBW343 and FLW29 to unravel defense related genes and pathways contributing to stripe rust resistance in wheat

Stripe rust (Sr), caused by Puccinia striiformis f. sp. tritici (Pst), is the most devastating disease that poses serious threat to the wheat-growing nations across the globe. Developing resistant cultivars is the most challenging aspect in wheat breeding. The function of resistance genes (R genes) and the mechanisms by which they influence plant-host interactions are poorly understood. In the present investigation, comparative transcriptome analysis was carried out by involving two near-isogenic lines (NILs) PBW343 and FLW29. The seedlings of both the genotypes were inoculated with Pst pathotype 46S119. In total, 1106 differentially expressed genes (DEGs) were identified at early stage of infection (12 hpi), whereas expressions of 877 and 1737 DEGs were observed at later stages (48 and 72 hpi) in FLW29. The identified DEGs were comprised of defense-related genes including putative R genes, 7 WRKY transcriptional factors, calcium, and hormonal signaling associated genes. Moreover, pathways involved in signaling of receptor kinases, G protein, and light showed higher expression in resistant cultivar and were common across different time points. Quantitative real-time PCR was used to further confirm the transcriptional expression of eight critical genes involved in plant defense mechanism against stripe rust. The information about genes are likely to improve our knowledge of the genetic mechanism that controls the stripe rust resistance in wheat, and data on resistance response-linked genes and pathways will be a significant resource for future research.

Comparative Transcriptome and Widely Targeted Metabolome Analysis Reveals the Molecular Mechanism of Powdery Mildew Resistance in Tomato

Powdery mildew is a serious problem in tomato production; therefore, the PM-resistant tomato inbred line, '63187', and the susceptible tomato variety, 'Moneymaker (MM)', were used as experimental materials for the combined analysis of transcriptome and widely targeted metabolome on tomato leaves at 0 h post inoculation (hpi), 12 hpi, and 48 hpi. The results indicated that 276 genes were expressed in all treatments, and the K-means cluster analysis showed that these genes were divided into eight classes in '63187' and ten classes in 'MM'. KEGG enrichment showed that amino acid metabolism, signal transduction, energy metabolism, and other secondary metabolites biosynthesis pathways were significantly enriched. Interestingly, the analysis of WRKY family transcription factors (TFs) showed that the expression of four TFs in '63187' increased with no obvious change in 'MM'; and the expression of one TF in 'MM' increased with no obvious change in '63187'. The combined analysis revealed that both phenylpropanoid biosynthesis and flavonoid biosynthesis pathways were enriched in '63187' and 'MM'. In '63187', six metabolites involved in this pathway were downregulated, and four genes were highly expressed, while in 'MM', three metabolites were upregulated, four metabolites were downregulated, and ten genes were highly expressed. These metabolites and genes might be candidates for PM resistance or susceptibility in subsequent studies. These results provide favorable molecular information for the study of the different resistances of tomatoes to PM, and they provide a basis for the breeding of tomato varieties resistant to PM.

Expression of ZmNAGK in tobacco enhances heat stress tolerance via activation of antioxidant-associated defense

Heat stress severely inhibits plant growth and limits crop yields. Thus, it is crucial to identify genes that are associated with plant heat stress responses. Here, we report a maize (Zea mays L.) gene, N-acetylglutamate kinase (ZmNAGK), that positively enhances plant heat stress tolerance. The ZmNAGK expression level was significantly up-regulated by heat stress in maize plants, and ZmNAGK was found to be localized in maize chloroplasts. Phenotypic analysis showed that overexpressing of ZmNAGK enhanced the tolerance of tobacco to heat stress both in the seed germination and seedling growth stages. Further physiological analysis showed that ZmNAGK overexpression in tobacco could alleviate oxidative damages that occurred during heat stress via activation of antioxidant defense signaling. Transcriptome analysis revealed that ZmNAGK could modulate the expression of antioxidant-enzyme encoding genes, such as ascorbate peroxidase 2 (APX2) and superoxide dismutase C (SODC), and heat shock network genes. Taken together, we have identified a maize gene that can provide plants with heat tolerance through the induction of antioxidant-associated defense signaling.

Advances in the Research on Plant WRKY Transcription Factors Responsive to External Stresses

The WRKY transcription factors are a class of transcriptional regulators that are ubiquitous in plants, wherein they play key roles in various physiological activities, including responses to stress. Specifically, WRKY transcription factors mediate plant responses to biotic and abiotic stresses through the binding of their conserved domain to the W-box element of the target gene promoter and the subsequent activation or inhibition of transcription (self-regulation or cross-regulation). In this review, the progress in the research on the regulatory effects of WRKY transcription factors on plant responses to external stresses is summarized, with a particular focus on the structural characteristics, classifications, biological functions, effects on plant secondary metabolism, regulatory networks, and other aspects of WRKY transcription factors. Future research and prospects in this field are also proposed.

Metabolomics and Transcriptomics Reveal the Response Mechanisms of Mikania micrantha to Puccinia spegazzinii Infection

Mikania micrantha is one of the 100 worst invasive species globally and can cause significant negative impacts on agricultural and forestry economics, particularly in Asia and the Pacific region. The rust Puccinia spegazzinii has been used successfully as a biological control agent in several countries to help manage M. micrantha. However, the response mechanisms of M. micrantha to P. spegazzinii infection have never been studied. To investigate the response of M. micrantha to infection by P. spegazzinii, an integrated analysis of metabolomics and transcriptomics was performed. The levels of 74 metabolites, including organic acids, amino acids, and secondary metabolites in M. micrantha infected with P. spegazzinii, were significantly different compared to those in plants that were not infected. After P. spegazzinii infection, the expression of the TCA cycle gene was significantly induced to participate in energy biosynthesis and produce more ATP. The content of most amino acids, such as L-isoleucine, L-tryptophan and L-citrulline, increased. In addition, phytoalexins, such as maackiain, nobiletin, vasicin, arachidonic acid, and JA-Ile, accumulated in M. micrantha. A total of 4978 differentially expressed genes were identified in M. micrantha infected by P. spegazzinii. Many key genes of M. micrantha in the PTI (pattern-triggered immunity) and ETI (effector-triggered immunity) pathways showed significantly higher expression under P. spegazzinii infection. Through these reactions, M. micrantha is able to resist the infection of P. spegazzinii and maintain its growth. These results are helpful for us to understand the changes in metabolites and gene expression in M. micrantha after being infected by P. spegazzinii. Our results can provide a theoretical basis for weakening the defense response of M. micrantha to P. spegazzinii, and for P. spegazzinii as a long-term biological control agent of M. micrantha.

The Karrikin Receptor Karrikin Insensitive2 Positively Regulates Heat Stress Tolerance in Arabidopsis thaliana

In this study, we investigated the potential role of the karrikin receptor KARRIKIN INSENSITIVE2 (KAI2) in the response of Arabidopsis seedlings to high-temperature stress. We performed phenotypic, physiological and transcriptome analyses of Arabidopsis kai2 mutants and wild-type (WT) plants under control (kai2_C and WT_C, respectively) and 6- and 24-h heat stress conditions (kai2_H6, kai2_H24, WT_H6 and WT_H24, respectively) to understand the basis for KAI2-regulated heat stress tolerance. We discovered that the kai2 mutants exhibited hypersensitivity to high-temperature stress relative to WT plants, which might be associated with a more highly increased leaf surface temperature and cell membrane damage in kai2 mutant plants. Next, we performed comparative transcriptome analysis of kai2_C, kai2_H6, kai2_H24, WT_C, WT_H6 and WT_H24 to identify transcriptome differences between WT and kai2 mutants in response to heat stress. K-mean clustering of normalized gene expression separated the investigated genotypes into three clusters based on heat-treated and non-treated control conditions. Within each cluster, the kai2 mutants were separated from WT plants, implying that kai2 mutants exhibited distinct transcriptome profiles relative to WT plants. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses showed a repression in 'misfolded protein binding', 'heat shock protein binding', 'unfolded protein binding' and 'protein processing in endoplasmic reticulum' pathways, which was consistent with the downregulation of several genes encoding heat shock proteins and heat shock transcription factors in the kai2 mutant versus WT plants under control and heat stress conditions. Our findings suggest that chemical or genetic manipulation of KAI2 signaling may provide a novel way to improve heat tolerance in plants.

A R2R3 MYB Transcription Factor, TaMYB391, Is Positively Involved in Wheat Resistance to Puccinia striiformis f. sp. tritici

A biotrophic fungus, Puccinia striiformis f.sp. tritici (Pst), which causes stripe rust disease in wheat is the most yield-limiting factor in wheat production. Plants have complex defense mechanisms against invading pathogens. Hypersensitive response (HR), a kind of programmed cell death (PCD) at the infection site, is among these defense mechanisms. Transcription factors (TFs) play a crucial role in plant defense response against invading pathogens. Myeloblastosis (MYB) TFs are among the largest TFs families that are involved in response to both biotic and abiotic stresses. However, little is known about the mechanisms of MYB TFs during the interaction between wheat and the stripe rust fungus. Here, we identified an R2R3 MYB TF from wheat, designated as TaMYB391, and characterized its functional role during wheat-Pst interaction. Our data indicated that TaMYB391 is induced by Pst infection and exogenous application of salicylic acid (SA) and abscisic acid (ABA). TaMYB391 is localized in the nucleus of both wheat and Nicotiana benthamiana. Transient overexpression of TaMYB391 in N. benthamiana triggered HR-related PCD accompanied by increased electrolyte leakage, high accumulation of reactive oxygen species (ROS), and transcriptional accumulation of SA defense-related genes and HR-specific marker genes. Overexpression of TaMYB391 in wheat significantly enhanced wheat resistance to stripe rust fungus through the induction of pathogenesis-related (PR) genes, ROS accumulation and hypersensitive cell death. On the other hand, RNAi-mediated silencing of TaMYB391 decreased the resistance of wheat to Pst accompanied by enhanced growth of the pathogen. Together our findings demonstrate that TaMYB391 acts as a positive regulator of HR-associated cell death and positively contributes to the resistance of wheat to the stripe rust fungus by regulating certain PR genes, possibly through SA signaling pathways.

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.

Harnessing genetic resistance to rusts in wheat and integrated rust management methods to develop more durable resistant cultivars

Wheat is one of the most important staple foods on earth. Leaf rust, stem rust and stripe rust, caused by Puccini triticina, Puccinia f. sp. graminis and Puccinia f. sp. striiformis, respectively, continue to threaten wheat production worldwide. Utilization of resistant cultivars is the most effective and chemical-free strategy to control rust diseases. Convectional and molecular biology techniques identified more than 200 resistance genes and their associated markers from common wheat and wheat wild relatives, which can be used by breeders in resistance breeding programmes. However, there is continuous emergence of new races of rust pathogens with novel degrees of virulence, thus rendering wheat resistance genes ineffective. An integration of genomic selection, genome editing, molecular breeding and marker-assisted selection, and phenotypic evaluations is required in developing high quality wheat varieties with resistance to multiple pathogens. Although host genotype resistance and application of fungicides are the most generally utilized approaches for controlling wheat rusts, effective agronomic methods are required to reduce disease management costs and increase wheat production sustainability. This review gives a critical overview of the current knowledge of rust resistance, particularly race-specific and non-race specific resistance, the role of pathogenesis-related proteins, non-coding RNAs, and transcription factors in rust resistance, and the molecular basis of interactions between wheat and rust pathogens. It will also discuss the new advances on how integrated rust management methods can assist in developing more durable resistant cultivars in these pathosystems.

A Group I WRKY Gene, TaWRKY133, Negatively Regulates Drought Resistance in Transgenic Plants

WRKYs are one of the largest transcription factor (TF) families and play an important role in plant resistance to various stresses. TaWRKY133, a group I WRKY protein, responds to a variety of abiotic stresses, including PEG treatment. The TaWRKY133 protein is located in the nucleus of tobacco epidermal cells, and both its N-terminal and C-terminal domains exhibit transcriptional activation activity. Overexpression of TaWRKY133 reduced drought tolerance in Arabidopsis thaliana, as reflected by a lower germination rate, shorter roots, higher stomatal aperture, poorer growth and lower antioxidant enzyme activities under drought treatment. Moreover, expression levels of stress-related genes (DREB2A, RD29A, RD29B, ABF1, ABA2, ABI1, SOD (Cu/Zn), POD1 and CAT1) were downregulated in transgenic Arabidopsis under drought stress. Gene silencing of TaWRKY133 enhanced the drought tolerance of wheat, as reflected in better growth, higher antioxidant enzyme activities, and higher expression levels of stress-related genes including DREB1, DREB3, ABF, ERF3, SOD (Fe), POD, CAT and P5CS. In conclusion, these results suggest that TaWRKY133 might reduce drought tolerance in plants by regulating the expression of stress-related genes.

A Puccinia striiformis f. sp. tritici effector inhibits high-temperature seedling-plant resistance in wheat

Resistance to Pseudomonas syringae pv. maculicola 1 (RPM1)-induced protein kinase (RIPK) in Arabidopsis belongs to the receptor-like cytoplasmic kinase (RLCK) family and plays a vital role in immunity. However, the role of RLCKs in the high-temperature seedling-plant (HTSP) resistance of wheat (Triticum aestivum) to Puccinia striiformis f. sp. tritici (Pst), the stripe rust pathogen, remains unclear. Here, we identified a homologous gene of RIPK in wheat, namely TaRIPK. Expression of TaRIPK was induced by Pst inoculation and high temperatures. Silencing of TaRIPK reduced the expression level of TaRPM1, resulting in weaker HTSP resistance. Moreover, TaRIPK interacts with and phosphorylates papain-like cysteine protease 1 (TaPLCP1). Meanwhile, we found that the Pst-secreted protein PSTG_01766 targets TaPLCP1. Transient expression of PSTG_01766 inhibited basal immunity in tobacco (Nicotiana benthamiana) and wheat. The role of PSTG_01766 as an effector involved in HTSP resistance was further supported by host-induced gene silencing and bacterial type three secretion system-mediated delivery into wheat. PSTG_01766 inhibited the TaRIPK-induced phosphorylation of TaPLCP1. Furthermore, PSTG_01766 has the potential to influence the subcellular localization of TaPLCP1. Overall, we suggest that the TaRIPK-TaPLCP1-TaRPM1 module fits the guard model for disease resistance, participating in HTSP resistance. PSTG_01766 decreases HTSP resistance via targeting TaPLCP1. Guarded by wheat and attacked by Pst, TaPLCP1 may serve as a central hub of the defense response. Our findings improve the understanding of the molecular mechanism of wheat HTSP resistance, which may be an important strategy for controlling stripe rust in the face of global warming.

Transcriptome analysis provides insights into the bases of salicylic acid-induced resistance to anthracnose in sorghum

Key Message Transcriptome analysis of SA sensitive and tolerant lines indicates that SA enhances anthracnose resistance in sorghum by upregulating the expression of some immune-related genes and pathways.Abstract Anthracnose caused by the hemibiotrophic pathogen Colletotrichum sublineolum is one of the most destructive diseases of sorghum, the fifth most important cereal crop in the world. Salicylic acid (SA) is a phytohormone essential for plant immunity; however, the role of SA in sorghum resistance to anthracnose has not been well explored. In this study, we found that Colletotrichum sublineolum infection induced the expression of SA-responsive genes and that exogenous SA enhanced resistance to anthracnose in the sorghum line BTx623. To rule out the possibility that SA triggers anthracnose resistance in sorghum by its direct toxic function on pathogen, an SA-tolerant line, WHEATLAND, was identified, and we found that SA treatment could not induce anthracnose resistance in WHEATLAND. Then, SA-induced transcriptome changes during Colletotrichum sublineolum infection in BTx623 and WHEATLAND were analyzed to explore the molecular mechanism of SA-triggered resistance. SA pretreatment regulated the expression of 2125 genes in BTx623 but only 524 genes in WHEATLAND during Colletotrichum sublineolum infection. The cutin, suberine and wax biosynthesis pathway involved in the plant immune response and the flavonoid biosynthesis pathway involved in anthracnose resistance were enriched in BTx623-specifically upregulated genes. Additionally, some immune-related genes, including multiple resistance genes, were differentially expressed in BTx623 and WHEATLAND. Taken together, our results revealed the mechanisms of SA-induced anthracnose resistance in sorghum at the transcriptional level and shed light on the possibility of enhancing sorghum resistance to anthracnose by activating the SA signaling pathway by molecular breeding.

Transcriptome profiling reveals the genes and pathways involved in thermo-tolerance in wheat (Triticum aestivum L.) genotype Raj 3765

Wheat, one of the most widely consumed staple food crops globally, is relatively vulnerable to high temperature-induced heat stress. It is therefore essential to gain more insight into the comprehensive mechanism of thermotolerance of wheat in order to safeguard its production. In view of this, we analysed heat stress responsive transcriptome data of wheat to determine its gene expression level under heat stress. A total of 7990 DEGs, including 4483 up-regulated and 3507 down regulated genes were identified. Gene Ontology (GO) analysis categorized 3910 DEGs into different ontology families. 146 pathways involving 814 DEGs were enriched during KEGG analysis. Metabolic pathways and biosynthesis of secondary metabolites were the major pathways enriched. MYB (myeloblastosis) transcription factors (TFs) and many other TFs as bHLH, WRKY, NAC, ERF, were determined to be quite abundant in the DEGs. Since various reports indicate that these TFs play important role in plants abiotic stress, it is an indication that our DEGs are functional in heat stress tolerance. Verification of few selected DEGs using RT-qPCR produced expression levels similar to the transcriptome data. This indicates that the transcriptome data is reliable. These results could be helpful in enhancing our understanding of the mechanism underlying thermotolerance in wheat.

Current understanding of atypical resistance against fungal pathogens in wheat

Pathogens and pests are a major challenge to global food security. Around one hundred different pests and pathogens challenge wheat, one of the most important food crops in the world. Traditional worldwide use of a few key resistance genes in wheat cultivars has necessitated a diversification of the toolbox of resistance genes in wheat varieties over the coming decades to meet the global production demands. Recent advances in gene discovery and functional characterization of genetic resistance mechanisms in wheat reveal great diversity in the types and effectiveness of the underlying resistance genes. This article summarizes the recent developments in the discovery of non-traditional "atypical" resistance genes in wheat against diverse fungal pathogens.

Distribution of Puccinia striiformis f. sp. tritici Races and Virulence in Wheat Growing Regions of Kenya from 1970 to 2014

Stripe rust, caused by the fungal pathogen Puccinia striiformis f. sp. tritici, is a major threat to wheat (Triticum spp.) production worldwide. The objective of this study was to determine the virulence of P. striiformis f. sp. tritici races prevalent in the main wheat growing regions of Kenya, which includes Mt. Kenya, Eastern Kenya, and the Rift Valley (Central, Southern, and Northern Rift). Fifty P. striiformis f. sp. tritici isolates collected from 1970 to 1992 and from 2009 to 2014 were virulence phenotyped with stripe rust differential sets, and 45 isolates were genotyped with sequence characterized amplified region (SCAR) markers to differentiate the isolates and identify aggressive strains PstS1 and PstS2. Virulence corresponding to stripe rust resistance genes Yr1, Yr2, Yr3, Yr6, Yr7, Yr8, Yr9, Yr17, Yr25, and Yr27 and the seedling resistance in genotype Avocet S were detected. Ten races were detected in the P. striiformis f. sp. tritici samples obtained from 1970 to 1992, and three additional races were detected from 2009 to 2014, with a single race being detected in both periods. The SCAR markers detected both Pst1 and Pst2 strains in the collection. Increasing P. striiformis f. sp. tritici virulence was found in the Kenyan P. striiformis f. sp. tritici population, and different P. striiformis f. sp. tritici race groups were found to dominate different wheat growing regions. Moreover, recent P. striiformis f. sp. tritici races in East Africa indicated possible migration of some race groups into Kenya from other regions. This study is important in elucidating P. striiformis f. sp. tritici evolution and virulence diversity and useful in breeding wheat cultivars with effective resistance to stripe rust.

Selection of Candidate Genes Conferring Blast Resistance and Heat Tolerance in Rice through Integration of Meta-QTLs and RNA-Seq

Due to global warming, high temperature is a significant environmental stress for rice production. Rice (Oryza sativa L.), one of the most crucial cereal crops, is also seriously devastated by Magnaporthe oryzae. Therefore, it is essential to breed new rice cultivars with blast and heat tolerance. Although progress had been made in QTL mapping and RNA-seq analysis in rice in response to blast and heat stresses, there are few reports on simultaneously mining blast-resistant and heat-tolerant genes. In this study, we separately conducted meta-analysis of 839 blast-resistant and 308 heat-tolerant QTLs in rice. Consequently, 7054 genes were identified in 67 blast-resistant meta-QTLs with an average interval of 1.00 Mb. Likewise, 6425 genes were obtained in 40 heat-tolerant meta-QTLs with an average interval of 1.49 Mb. Additionally, using differentially expressed genes (DEGs) in the previous research and GO enrichment analysis, 55 DEGs were co-located on the common regions of 16 blast-resistant and 14 heat-tolerant meta-QTLs. Among, OsChib3H-c, OsJAMyb, Pi-k, OsWAK1, OsMT2b, OsTPS3, OsHI-LOX, OsACLA-2 and OsGS2 were the significant candidate genes to be further investigated. These results could provide the gene resources for rice breeding with excellent resistance to these 2 stresses, and help to understand how plants response to the combination stresses of blast fungus and high temperature.

The RLK protein TaCRK10 activates wheat high-temperature seedling-plant resistance to stripe rust through interacting with TaH2A.1

Plants sense various pathogens and activate immunity responses through receptor-like kinases (RLKs). Cysteine-rich receptor-like kinases (CRKs) are involved in massive transduction pathways upon perception of a pathogen. However, the roles of CRKs in response to stripe rust are unclear. In the present study, we identified a CRK gene (designated TaCRK10) from wheat variety Xiaoyan 6 (XY6) that harbors high-temperature seedling-plant (HTSP) resistance to stripe rust caused by fungal pathogen Puccinia striiformis f. sp. tritici (Pst). The expression level of TaCRK10 was induced by Pst inoculation and high temperature treatment. Knockdown of TaCRK10 by virus-induced gene silencing resulted in attenuated wheat HTSP resistance to Pst, whereas there is no effect on Pst development and host responses under normal temperatures. Notably, overexpression of TaCRK10 in susceptible variety Fielder provided resistance only under normal temperatures at 14 days with reactive oxygen species accumulation and defense-related gene expression of the salicylic acid pathway. Moreover, TaCRK10 physically interacted with and phosphorylated a histone variant TaH2A.1, which belongs to the H2A.W group. Silencing of TaH2A.1 suppressed wheat resistance to Pst, indicating that TaH2A.1 plays a positive role in wheat resistance to Pst. Thus, TaCRK10 serves as an important sensor of Pst infection and high temperatures, and it activates wheat resistance to Pst through regulating nuclear processes. This knowledge helps elucidate the molecular mechanism of wheat HTSP resistance to Pst and promotes efforts in developing wheat varieties with resistance to stripe rust.

GhWRKY21 regulates ABA-mediated drought tolerance by fine-tuning the expression of GhHAB in cotton

KEY MESSAGE

We report that GhWRKY21, a WRKY transcription factor, plays essential roles in regulating the intensity of the drought-induced ABA signalling pathway by facilitating the expression of GhHAB in cotton (Gossypium hirsutum). Abscisic acid (ABA) is one of the most important plant hormones in response to abiotic stress. However, activation of the ABA signalling pathway often leads to growth inhibition. The mechanisms that regulate the intensity of ABA signals are poorly understood. Here, we isolated and analysed the cotton group IId WRKY transcription factor (TF) gene GhWRKY21. Functional analysis indicated that GhWRKY21 plays a negative role in the drought response of cotton. Silencing of GhWRKY21 in cotton dramatically increased drought tolerance, whereas ectopic GhWRKY21 overexpression in Nicotiana benthamiana decreased drought tolerance. Furthermore, the GhWRKY21-mediated drought tolerance was ABA dependent. To clarify the mechanism underlying the GhWRKY21-mediated regulation of drought tolerance, 17 clade-A-type type 2C protein phosphatase (PP2C) genes, which are negative regulators of ABA signalling, were identified in cotton. Notably, GhWRKY21 interacted specifically with the W-box element within the promoter of GhHAB and regulated its expression. Silencing of GhHAB in cotton yielded a phenotype similar to that of GhWRKY21-silenced cotton. These results suggest that GhWRKY21 regulates the intensity of ABA signals by facilitating the expression of GhHAB. In summary, these findings dramatically improve our understanding of the function of WRKY TFs and provide insights into the mechanism of ABA-mediated drought tolerance.

Transcriptome Profiling of Maize (Zea mays L.) Leaves Reveals Key Cold-Responsive Genes, Transcription Factors, and Metabolic Pathways Regulating Cold Stress Tolerance at the Seedling Stage

Cold tolerance is a complex trait that requires a critical perspective to understand its underpinning mechanism. To unravel the molecular framework underlying maize (Zea mays L.) cold stress tolerance, we conducted a comparative transcriptome profiling of 24 cold-tolerant and 22 cold-sensitive inbred lines affected by cold stress at the seedling stage. Using the RNA-seq method, we identified 2237 differentially expressed genes (DEGs), namely 1656 and 581 annotated and unannotated DEGs, respectively. Further analysis of the 1656 annotated DEGs mined out two critical sets of cold-responsive DEGs, namely 779 and 877 DEGs, which were significantly enhanced in the tolerant and sensitive lines, respectively. Functional analysis of the 1656 DEGs highlighted the enrichment of signaling, carotenoid, lipid metabolism, transcription factors (TFs), peroxisome, and amino acid metabolism. A total of 147 TFs belonging to 32 families, including MYB, ERF, NAC, WRKY, bHLH, MIKC MADS, and C₂H₂, were strongly altered by cold stress. Moreover, the tolerant lines’ 779 enhanced DEGs were predominantly associated with carotenoid, ABC transporter, glutathione, lipid metabolism, and amino acid metabolism. In comparison, the cold-sensitive lines’ 877 enhanced DEGs were significantly enriched for MAPK signaling, peroxisome, ribosome, and carbon metabolism pathways. The biggest proportion of the unannotated DEGs was implicated in the roles of long non-coding RNAs (lncRNAs). Taken together, this study provides valuable insights that offer a deeper understanding of the molecular mechanisms underlying maize response to cold stress at the seedling stage, thus opening up possibilities for a breeding program of maize tolerance to cold stress.

WRKY Transcription Factor Response to High-Temperature Stress

Plant growth and development are closely related to the environment, and high-temperature stress is an important environmental factor that affects these processes. WRKY transcription factors (TFs) play important roles in plant responses to high-temperature stress. WRKY TFs can bind to the W-box cis-acting elements of target gene promoters, thereby regulating the expression of multiple types of target genes and participating in multiple signaling pathways in plants. A number of studies have shown the important biological functions and working mechanisms of WRKY TFs in plant responses to high temperature. However, there are few reviews that summarize the research progress on this topic. To fully understand the role of WRKY TFs in the response to high temperature, this paper reviews the structure and regulatory mechanism of WRKY TFs, as well as the related signaling pathways that regulate plant growth under high-temperature stress, which have been described in recent years, and this paper provides references for the further exploration of the molecular mechanisms underlying plant tolerance to high temperature.

The whole-genome and expression profile analysis of WRKY and RGAs in Dactylis glomerata showed that DG6C02319.1 and DgWRKYs may cooperate in the immunity against rust

Orchardgrass (Dactylis glomerata) is one of the top four perennial forages worldwide and, despite its large economic advantages, often threatened by various environmental stresses. WRKY transcription factors (TFs) can regulate a variety of plant processes, widely participate in plant responses to biotic and abiotic stresses, and are one of the largest gene families in plants. WRKYs can usually bind W-box elements specifically. In this study, we identified a total of 93 DgWRKY genes and 281 RGAs, including 65, 169 and 47 nucleotide-binding site-leucine-rich repeats (NBS-LRRs), leucine-rich repeats receptor-like protein kinases (LRR-RLKs), and leucine-rich repeats receptor-like proteins (LRR-RLPs), respectively. Through analyzing the expression of DgWRKY genes in orchardgrass under different environmental stresses, it was found that many DgWRKY genes were differentially expressed under heat, drought, submergence, and rust stress. In particular, it was found that the greatest number of genes were differentially expressed under rust infection. Consistently, GO and KEGG enrichment analysis of all genes showed that 78 DgWRKY TFs were identified in the plant–pathogen interaction pathway, with 59 of them differentially expressed. Through cis-acting element prediction, 154 RGAs were found to contain W-box elements. Among them, DG6C02319.1 (a member of the LRR-RLK family) was identified as likely to interact with 14 DGWRKYs. Moreover, their expression levels in susceptible plants after rust inoculation were first up-regulated and then down-regulated, while those in the resistant plants were always up-regulated. In general, DgWRKYs responded to both biotic stress and abiotic stress. DgWRKYs and RGAs may synergistically respond to the response of orchardgrass to rust. This study provides meaningful insight into the molecular mechanisms of WRKY proteins in orchardgrass.

Unraveling the Genome of a High Yielding Colombian Sugarcane Hybrid

Recent developments in High Throughput Sequencing (HTS) technologies and bioinformatics, including improved read lengths and genome assemblers allow the reconstruction of complex genomes with unprecedented quality and contiguity. Sugarcane has one of the most complicated genomes among grassess with a haploid length of 1Gbp and a ploidies between 8 and 12. In this work, we present a genome assembly of the Colombian sugarcane hybrid CC 01-1940. Three types of sequencing technologies were combined for this assembly: PacBio long reads, Illumina paired short reads, and Hi-C reads. We achieved a median contig length of 34.94 Mbp and a total genome assembly of 903.2 Mbp. We annotated a total of 63,724 protein coding genes and performed a reconstruction and comparative analysis of the sucrose metabolism pathway. Nucleotide evolution measurements between orthologs with close species suggest that divergence between Saccharum officinarum and Saccharum spontaneum occurred <2 million years ago. Synteny analysis between CC 01-1940 and the S. spontaneum genome confirms the presence of translocation events between the species and a random contribution throughout the entire genome in current sugarcane hybrids. Analysis of RNA-Seq data from leaf and root tissue of contrasting sugarcane genotypes subjected to water stress treatments revealed 17,490 differentially expressed genes, from which 3,633 correspond to genes expressed exclusively in tolerant genotypes. We expect the resources presented here to serve as a source of information to improve the selection processes of new varieties of the breeding programs of sugarcane.

NBS-LRR Gene TaRPS2 is Positively Associated with the High-Temperature Seedling Plant Resistance of Wheat Against Puccinia striiformis f. sp. tritici

Xiaoyan6 (XY6) is a wheat (Triticum aestivum) cultivar possessing nonrace-specific high-temperature seedling plant (HTSP) resistance against stripe rust, caused by Puccinia striiformis f. sp. tritici. Previously, we identified one particular gene, TaRPS2, for its involvement in the HTSP resistance. To elucidate the role of TaRPS2 in the HTSP resistance, we cloned the full length of TaRPS2 from XY6. The transcriptional expression of TaRPS2 was rapidly upregulated (19.11-fold) under the normal-high-normal temperature treatment that induces the HTSP resistance. The expression level of TaRPS2 in leaves was higher than that in the stems and roots. Quantification of the endogenous hormones in wheat leaves after P. striiformis f. sp. tritici inoculation showed that 1-aminocyclopropane-1-carboxylic acid, salicylic acid (SA), and jasmonic acid were involved in the HTSP resistance. In addition, detection of hydrogen peroxide (H₂O₂) accumulation indicated that reactive oxygen species burst was also associated with the HTSP resistance. Two hours after exogenous H₂O₂ treatment or 0.5 h after SA treatment, the expression level of TaRPS2 was increased by 2.66 and 2.35 times, respectively. The subcellular localization of enhanced green fluorescent protein-TaRPS2 fusion protein was in the nuclei and plasma membranes. Virus-induced gene silencing of TaRPS2 reduced the level of HTSP resistance in XY6. Compared with the nonsilenced leaves, the TaRPS2-silenced leaves had the reduction of necrotic cells but a greater number of uredinia. These results indicated that TaRPS2 positively regulates the HTSP resistance of XY6 against P. striiformis f. sp. tritici and is related to the SA and H₂O₂ signaling pathways.

Transcriptome-wide identification of WRKY family genes and their expression profiling toward salicylic acid in Camellia japonica

The ornamental plant Camellia japonica is widely distributed worldwide and is susceptible to various environmental stresses. The WRKY transcription factor (TF) is an important node of plant tolerance. However, WRKY TFs from C. japonica have not been reported yet. In this study, 48 CjWRKYs, namely, CjWRKY1 to CjWRKY48, were identified. Protein structure analysis revealed that CjWRKY proteins contain a highly conserved motif (WRKYGQK) and two variant motifs (WRKYGKK and WRKYGRK). Phylogenetic analysis indicated that the 48 CjWRKYs can be divided into three groups, which are further classified into six subgroups, namely, I-C, II-a, II-b, II-c, II-e, and III, which contain 10, 6, 8, 13, 7, and 4 members, respectively. The expression patterns of 15 CjWRKYs under salicylic acid (SA) treatment were investigated by real-time quantitative PCR (qRT-PCR). Results showed that the 15 CjWRKYs could be induced by SA treatment. This study is the first to screen CjWRKYs and identify the expression profile of CjWRKYs under SA treatment and provides a theoretical basis for analyzing the function of CjWRKY genes to SA stress tolerance in C. japonica.

Chrysanthemum WRKY15-1 promotes resistance to Puccinia horiana Henn. via the salicylic acid signaling pathway

Chrysanthemum white rust disease, which is caused by the fungus Puccinia horiana Henn., severely reduces the ornamental quality and yield chrysanthemum. WRKY transcription factors function in the disease-resistance response in a variety of plants; however, it is unclear whether members of this family improve resistance to white rust disease in chrysanthemum. In this study, using PCR, we isolated a WRKY15 homologous gene, CmWRKY15-1, from the resistant chrysanthemum cultivar C029. Real-time quantitative PCR (RT-qPCR) revealed that CmWRKY15-1 exhibited differential expression patterns between the immune cultivar C029 and the susceptible cultivar Jinba upon P. horiana infection. In addition, salicylic acid (SA) treatment strongly induced CmWRKY15-1 expression. Overexpression of CmWRKY15-1 in the chrysanthemum-susceptible cultivar Jinba increased tolerance to P. horiana infection. Conversely, silencing CmWRKY15-1 via RNA interference (RNAi) in C029 increased sensitivity to P. horiana infection. We also determined that P. horiana infection increased both the endogenous SA content and the expression of salicylic acid biosynthesis genes in CmWRKY15-1-overexpressing plants, whereas CmWRKY15-1 RNAi plants exhibited the opposite effects under the same conditions. Finally, the transcript levels of pathogenesis-related (PR) genes involved in the SA pathway were positively associated with CmWRKY15-1 expression levels. Our results demonstrated that CmWRKY15-1 plays an important role in the resistance of chrysanthemum to P. horiana by influencing SA signaling.

Overexpression of JcWRKY2 confers increased resistance towards Macrophomina phaseolina in transgenic tobacco

WRKY proteins are plant-specific transcription factors (TFs), and form one of the largest families and are involved in plant development and responses to stress. The salicylic acid (SA) responsive WRKY family auto or cross-regulate the defence stress signalling pathways. In this study, we functionally validated the role of JcWRKY2 gene from biofuel crop Jatropha curcas towards improving resistance to tobacco transgenic against charcoal rot causing necrotrophic fungus, Macrophomina phaseolina. The microscopic studies revealed that JcWRKY2 participated in preventing the spread of infection in transgenic. The generation of H2O2 during M. phaseolina and combinatorial stress in transgenic induces the expression and activity of antioxidant enzymes. The transcript expression of SA biosynthetic (NtICS1) gene, pathogenesis-related (NtPR-10) gene and antioxidative enzymes (NtCAT1 and NtSOD) gene revealed that JcWRKY2 transgenic play a role in SA-mediated, antioxidative enzymes regulation during biotic challenges. The study highlights the potential of JcWRKY2 as an important regulator for plant biotic stress responses through the SA-dependent pathway.

Phytohormone crosstalk in the host-Verticillium interaction

Functional genomics can be applied to shed light on the Brassica napus - Verticillium interaction. RNAseq data indicated already that abscisic acid (ABA) is apparently involved in the early oilseed rape response to fungal infection with Verticillium longisporum isolate 43 (Vl43). A calreticulin (CRT1a) was identified as novel susceptibility factor for Vl43 infecting both Arabidopsis and oilseed rape. CRT1a is involved in calcium homeostasis and contributes in the endoplasmatic reticulum to the unfolded protein response. The latter function could either affect the correct folding of other susceptibility factors or of negative regulators in ethylene (ET) signaling. Which CRT1a function is affected in the mutants is currently unknown, but both hypotheses can explain that crt1a loss-of-function mutants display increased resistance to V. longisporum and enhanced expression of ethylene signaling related genes. This indicates that besides other phytohormones such as ABA or salicylic acid (SA) also ET plays a critical role in the plant-Verticillium interaction, which might be exploited to improve plant resistance.

A wheat R2R3 MYB gene TaMpc1-D4 negatively regulates drought tolerance in transgenic Arabidopsis and wheat

MYB transcription factors (TFs) are one of the largest TF families, and R2R3-type MYB TFs participate in the multiply abiotic stress responses in wheat. In this study, an R2R3-type MYB gene Myb protein colourless 1 located on chromosome D (named TaMpc1-D4), was cloned from wheat. TaMpc1-D4-GFP protein was localized in the nucleus. Overexpression of TaMpc1-D4 reduced drought tolerance in transgenic Arabidopsis lines, which was supported by the lower germination rate, the shorter root length, a higher level of O₂^- and malonaldehyde (MDA), the decreased proline content, and limited activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT). Furthermore, P5CS1, RD29A, RD29B, DREB2A, ABF3, CBF1, CBF2, CBF3, ERF1, POD1, SOD (Cu/Zn), and CAT1 genes related to the stress and antioxidant system were remarkably down-regulated in TaMpc1-D4 transgenic Arabidopsis lines under drought stress. Silencing TaMpc1-D4 expression in wheat enhanced the relative water content (RWC), the proline content, and the activities of antioxidant enzymes, and activated stress-related and antioxidant-related genes (DREB1, DREB3, ERF3, ERF4b, ABF, P5CS, POD, SOD (Fe), and CAT). Taken together, these results indicated that TaMpc1-D4 negatively modulated drought tolerance by regulating the capacity of the enzyme system and the expression of stress-related and antioxidant-related genes.

High temperature-induced plant disease susceptibility: more than the sum of its parts

Higher temperatures associated with climate change often increase the severity of plant diseases. An understanding of how plants respond to pathogens during high temperature stress is required for crop improvement, but the molecular mechanisms underlying this response are largely unknown. Mechanistic research has primarily focused on plant responses during either single stresses or heat-induced loss of single gene resistance. Transcriptome analyses of plant responses to a single stress compared to combined-stresses reveal significant differences showing that single-stress response studies are inadequate for determining the mechanisms of high temperature-induced disease susceptibility. To combat plant disease in light of climate change, future research will require comprehensive study designs and analyses.

Inhibition of multiple defense responsive pathways by CaWRKY70 transcription factor promotes susceptibility in chickpea under Fusarium oxysporum stress condition

BACKGROUND

Suppression and activation of plant defense genes is comprehensively regulated by WRKY family transcription factors. Chickpea, the non-model crop legume suffers from wilt caused by Fusarium oxysporum f. sp. ciceri Race1 (Foc1), defense response mechanisms of which are poorly understood. Here, we attempted to show interaction between WRKY70 and several downstream signaling components involved in susceptibility/resistance response in chickpea upon challenge with Foc1.

RESULTS

In the present study, we found Cicer arietinum L. WRKY70 (CaWRKY70) negatively governs multiple defense responsive pathways, including Systemic Acquired Resistance (SAR) activation in chickpea upon Foc1 infection. CaWRKY70 is found to be significantly accumulated at shoot tissues of susceptible (JG62) chickpea under Foc1 stress and salicylic acid (SA) application. CaWRKY70 overexpression promotes susceptibility in resistant chickpea (WR315) plants to Foc1 infection. Transgenic plants upon Foc1 inoculation demonstrated suppression of not only endogenous SA concentrations but expression of genes involved in SA signaling. CaWRKY70 overexpressing chickpea roots exhibited higher ion-leakage and Foc1 biomass accumulation compared to control transgenic (VC) plants. CaWRKY70 overexpression suppresses H₂O₂ production and resultant reactive oxygen species (ROS) induced cell death in Foc1 infected chickpea roots, stem and leaves. Being the nuclear targeted protein, CaWRKY70 suppresses CaMPK9-CaWRKY40 signaling in chickpea through its direct and indirect negative regulatory activities. Protein-protein interaction study revealed CaWRKY70 and CaRPP2-like CC-NB-ARC-LRR protein suppresses hyper-immune signaling in chickpea. Together, our study provides novel insights into mechanisms of suppression of the multiple defense signaling components in chickpea by CaWRKY70 under Foc1 stress.

CONCLUSION

CaWRKY70 mediated defense suppression unveils networking between several immune signaling events negatively affecting downstream resistance mechanisms in chickpea under Foc1 stress.

Revealing Differentially Expressed Genes and Identifying Effector Proteins of Puccinia striiformis f. sp. tritici in Response to High-Temperature Seedling Plant Resistance of Wheat Based on Transcriptome Sequencing

In the present study, we performed transcriptomic analysis to identify differentially expressed genes and effector proteins of Puccinia striiformis f. sp. tritici ( Pst ) in response to the high-temperature seedling-plant (HTSP) resistance in wheat. Experimental validation confirmed the function of the highest upregulated effector protein, PstCEP1. This study provides a key resource for understanding the biology and molecular basis of Pst responses to wheat HTSP resistance, and PstCEP1 may be used in future studies to understand pathogen-associated molecular pattern-triggered immunity and effector-triggered immunity processes in the Pst -wheat interaction system.

Two light responsive WRKY genes exhibit positive and negative correlation with picroside content in Picrorhiza kurrooa Royle ex Benth, an endangered medicinal herb

Picrorhiza kurrooa is an endangered herb known to produce the medicinally important picrosides through isoprenoid pathway. The present work showed the functionality of WRKY motifs (TGAC cis-acting elements) present in the promoters of regulatory genes 3-hydroxy-3-methylglutaryl coenzyme A reductase (Pkhmgr) and 1-deoxy-d-xylulose-5-phosphate synthase (Pkdxs) of the picrosides biosynthetic pathway by electrophoretic mobility shift assay. Also, the two WRKY genes, PkdWRKY and PksWRKY, were characterized and found to contain double and single characteristic WRKY domains, respectively along with a zinc-finger motif in each domain. Expression analysis revealed that PkdWRKY and PksWRKY exhibited a positive and negative correlation, respectively, with picrosides content under the environment of light and in different tissues. Functional evaluation in yeast showed DNA binding ability of both PksWRKY and PkdWRKY; however, only PkdWRKY exhibited transcriptional activation ability. Transient overexpression of PkdWRKY and PksWRKY in tobacco modulated the expression of selected native genes of tobacco involved in MVA and MEP pathway suggesting functionality of PkdWRKY and PksWRKY in planta. Collectively, data suggested that PkdWRKY and PksWRKY might be positive and negative regulators, respectively in the picrosides biosynthetic pathway.

Transcription Factors in Plant Stress Responses: Challenges and Potential for Sugarcane Improvement

Increasing vulnerability of crops to a wide range of abiotic and biotic stresses can have a marked influence on the growth and yield of major crops, especially sugarcane (Saccharum spp.). In response to various stresses, plants have evolved a variety of complex defense systems of signal perception and transduction networks. Transcription factors (TFs) that are activated by different pathways of signal transduction and can directly or indirectly combine with cis-acting elements to modulate the transcription efficiency of target genes, which play key regulators for crop genetic improvement. Over the past decade, significant progresses have been made in deciphering the role of plant TFs as key regulators of environmental responses in particular important cereal crops; however, a limited amount of studies have focused on sugarcane. This review summarizes the potential functions of major TF families, such as WRKY, NAC, MYB and AP2/ERF, in regulating gene expression in the response of plants to abiotic and biotic stresses, which provides important clues for the engineering of stress-tolerant cultivars in sugarcane.

A Wheat WRKY Transcription Factor TaWRKY46 Enhances Tolerance to Osmotic Stress in transgenic Arabidopsis Plants

WRKY transcription factors play central roles in developmental processes and stress responses of wheat. Most WRKY proteins of the same group (Group III) have a similar function in abiotic stress responses in plants. TaWRKY46, a member of Group III, was up-regulated by PEG treatment. TaWRKY46-GFP fusion proteins localize to the nucleus in wheat mesophyll protoplasts. Overexpression of TaWRKY46 enhanced osmotic stress tolerance in transgenic Arabidopsis thaliana plants, which was mainly demonstrated by transgenic Arabidopsis plants forming higher germination rate and longer root length on 1/2 Murashige and Skoog (MS) medium containing mannitol. Furthermore, the expression of several stress-related genes (P5CS1, RD29B, DREB2A, ABF3, CBF2, and CBF3) was significantly increased in TaWRKY46-overexpressing transgenic Arabidopsis plants after mannitol treatment. Taken together, these findings proposed that TaWRKY46 possesses vital functions in improving drought tolerance through ABA-dependent and ABA-independent pathways when plants are exposed to adverse osmotic conditions. TaWRKY46 can be taken as a candidate gene for transgenic breeding against osmotic stress in wheat. It can further complement and improve the information of the WRKY family members of Group III.

GhWRKY70D13 Regulates Resistance to Verticillium dahliae in Cotton Through the Ethylene and Jasmonic Acid Signaling Pathways

Verticillium wilt caused by Verticillium dahliae is a destructive cotton disease causing severe yield and quality losses worldwide. WRKY transcription factors play important roles in plant defense against pathogen infection. However, little has been reported on the functions of WRKYs in cotton's resistance to V. dahliae. Here, we identified 5, 5, and 10 WRKY70 genes in Gossypium arboreum, Gossypium raimondii, and Gossypium hirsutum, respectively, and investigated the expression profiles of all GhWRKY70 genes in various cotton tissues and in response to hormone treatment or V. dahliae infection. Reverse transcription-quantitative PCR analysis showed that GhWRKY70D13 was expressed higher in roots and stems than in other tissues, and up-regulated after V. dahliae inoculation. Knock-down of GhWRKY70D13 improved resistance to V. dahliae in both resistant and susceptible cotton cultivars. Comparative analysis of transcriptomes generated from wild-type and stable RNAi (RNA interference) plant with down-regulated GhWRKY70D13 showed that genes involved in ethylene (ET) and jasmonic acid (JA) biosynthesis and signaling were significantly upregulated in the GhWRKY70D13 RNAi plants. Consistently, the contents of 1-aminocyclopropane-1-carboxylic (ACC), JA, and JA-isoleucine levels were significantly higher in the GhWRKY70D13 RNAi plants than in wild-type. Following V. dahliae infection, the levels of ACC and JA decreased in the GhWRKY70D13 RNAi plants but still significantly higher (for ACC) than that in wild-type or at the same level (for JA) as in non-infected wild-type plants. Collectively, our results suggested that GhWRKY70D13 negatively regulates cotton's resistance to V. dahliae mainly through its effect on ET and JA biosynthesis and signaling pathways.

Effects of Stripe Rust Infection on the Levels of Redox Balance and Photosynthetic Capacities in Wheat

Wheat stripe rust (Puccinia striiformis f. sp. tritici, Pst) is the most destructive wheat disease and a major problem for the productivity of wheat in the world. To obtain a better understanding about different effects of redox homeostasis and photosystem (PS) to Pst infection in wheat, we investigated the differences in photosynthesis and the antioxidant defense system in wheat cultivar Chuanmai42 (CM42) in response to two Chinese Pst races known as CYR32 and V26. The results showed that V26-infected wheat accumulated a higher reactive oxygen species (ROS), cell death, and energy dissipation than CYR32-infected wheat when compared with the control. Furthermore, we found that the activities of three antioxidant enzymes (APX, GR, and GPX) and four resistance-related enzymes in CYR32-infected wheat were significantly higher than that in V26-infected wheat. In addition, quantitative RT-PCR indicated that the expression levels of two genes associated with resistant stripe rust in CYR32-infected wheat were clearly higher than that in V26-infected wheat. Compared with CYR32-infected wheat, lower photochemical efficiencies were observed in V26-infected wheat at the adult stage. Meanwhile, only a marked decline in D1 protein was observed in V26-infected wheat. We therefore deduced that wheat with stripe rust resistance could maintain high resistance and photosynthetic capacity by regulating the antioxidant system, disease-resistant related enzymes and genes, and the levels of PSII reaction center proteins.

TaXa21, a Leucine-Rich Repeat Receptor-Like Kinase Gene Associated with TaWRKY76 and TaWRKY62, Plays Positive Roles in Wheat High-Temperature Seedling Plant Resistance to Puccinia striiformis f. sp. tritici

Puccinia striiformis f. sp. tritici causes wheat stripe rust, one of most important diseases of wheat worldwide. High-temperature seedling plant (HTSP) resistance of wheat to P. striiformis f. sp. tritici is one specific type of host resistance, induced by high temperature (HT). Receptor-like kinases (RLKs) play key roles in regulating plant development and signaling networks, but there have been no reports on possible roles played by RLKs in wheat HTSP to P. striiformis f. sp. tritici. In the present study, a leucine rich repeat (LRR)-RLK gene, TaXa21, with a high homology with rice bacterial blight resistance gene Xa21, was cloned from wheat cultivar Xiaoyan 6 (XY 6). TaXa21 expression was up-regulated by the exposure to HT (20°C) for 24 h at 8 days postinoculation with P. striiformis f. sp. tritici and was induced by ethylene (ET) and hydrogen peroxide (H₂O₂). Knocking down TaXa21 using virus-induced gene silencing reduced HTSP resistance to P. striiformis f. sp. tritici compared with the control plants. In addition, the expression level of TaCAT in the H₂O₂ pathway was induced and TaACO in the ET signal pathway was reduced in the HT-treated TaXa21-silenced plants. Transient expression of TaXa21 in tobacco leaves confirmed its subcellular localization in plasma membrane, consistent with the prediction from bioinformatics analysis. The transmembrane and kinase domain of TaXa21 can interact with TaWRKY76 in the nucleus and cell membrane, which is different from the localization of Xa21 in rice. The interaction between TaWRKY76 and TaWRKY62 (positively involved in the HTSP resistance of XY 6) were observed. Together, these results indicated that TaXa21 is a RLK associated with TaWRKY76 and TaWRKY62 and functions as a positive regulator of wheat HTSP resistance to P. striiformis f. sp. tritici. Furthermore, the host defense is mediated by the H₂O₂ and ET signal pathways.

Comparative Transcriptome Analysis in Eggplant Reveals Selection Trends during Eggplant Domestication

Eggplant (Solanum melongena L.) is an economically and nutritionally important fruit crop of the Solanaceae family, which was domesticated in India and southern China. However, the genome regions subjected to selective sweeps in eggplant remain unknown. In the present study, we performed comparative transcriptome analysis of cultivated and wild eggplant species with emphasis on the selection pattern during domestication. In total, 44,073 (S. sisymbriifolium) to 58,677 (S. melongena cultivar S58) unigenes were generated for the six eggplant accessions with total lengths of 36.6-46 Mb. The orthologous genes were assessed using the ratio of nonsynonymous (K a) to synonymous (K s) nucleotide substitutions to characterize selective patterns during eggplant domestication. We identified 19 genes under positive selection across the phylogeny that were classified into four groups. The gene (OG12205) under positive selection was possibly associated with fruit-related traits in eggplant, which may have resulted from human manipulation. Eight positive selected genes were potentially involved in stress tolerance or disease resistance, suggesting that environmental changes and biotic stresses were important selective pressures in eggplant domestication. Taken together, our results shed light on the effects of artificial and natural selection on the transcriptomes of eggplant and its wild relatives. Identification of the selected genes will facilitate the understanding of genetic architecture of domesticated-related traits and provide resources for resistant breeding in eggplant.

TaRPM1 Positively Regulates Wheat High-Temperature Seedling-Plant Resistance to Puccinia striiformis f. sp. tritici

RPM1 is a CC-NBS-LRR protein that was first shown to be required for resistance to Pseudomonas syringae pv. maculicola in Arabidopsis thaliana. Our previous study showed that TaRPM1 gene in wheat was upregulated about six times following infection by Puccinia striiformis f. sp. tritici (Pst) under high temperature, compared with normal temperature. To study the function of TaRPM1 in wheat high-temperature seedling-plant (HTSP) resistance to Pst, the full length of TaRPM1 was cloned, with three copies each located on chromosomes 1A, 1B, and 1D. Transient expression of the TaRPM1-GFP fusion protein in Nicotiana benthamiana indicated that TaRPM1 localizes in the cytoplasm and nucleus. Profiling TaRPM1 expression indicated that TaRPM1 transcription was rapidly upregulated upon Pst inoculation under high temperature. In addition, TaRPM1 was induced by exogenous salicylic acid hormone application. Silencing TaRPM1 in wheat cultivar Xiaoyan 6 (XY 6) resulted in reduced HTSP resistance to Pst in terms of reduced number of necrotic cells and increased uredinial length, whereas no obvious phenotypic changes were observed in TaRPM1-silenced leaves under normal temperature. Related defense genes TaPR1 and TaPR2 were downregulated in TaRPM1-silenced plants under high temperature. We conclude that TaRPM1 is involved in HTSP resistance to Pst in XY 6.