PPI1: a novel pathogen-induced basic region-leucine zipper (bZIP) transcription factor from pepper

The Role of Plant Transcription Factors in the Fight against Plant Viruses

Plants are vulnerable to the challenges of unstable environments and pathogen infections due to their immobility. Among various stress conditions, viral infection is a major threat that causes significant crop loss. In response to viral infection, plants undergo complex molecular and physiological changes, which trigger defense and morphogenic pathways. Transcription factors (TFs), and their interactions with cofactors and cis-regulatory genomic elements, are essential for plant defense mechanisms. The transcriptional regulation by TFs is crucial in establishing plant defense and associated activities during viral infections. Therefore, identifying and characterizing the critical genes involved in the responses of plants against virus stress is essential for the development of transgenic plants that exhibit enhanced tolerance or resistance. This article reviews the current understanding of the transcriptional control of plant defenses, with a special focus on NAC, MYB, WRKY, bZIP, and AP2/ERF TFs. The review provides an update on the latest advances in understanding how plant TFs regulate defense genes expression during viral infection.

The bZIP Transcription Factor Family in Adzuki Bean (Vigna Angularis): Genome-Wide Identification, Evolution, and Expression Under Abiotic Stress During the Bud Stage

Adzuki bean (Vigna angularis) is an important dietary legume crop that was first cultivated and domesticated in Asia. Currently, little is known concerning the evolution and expression patterns of the basic leucine zipper (bZIP) family transcription factors in the adzuki bean. Through the PFAM search, 72 bZIP members of adzuki bean (VabZIP) were identified from the reference genome. Most of them were located on 11 chromosomes and seven on an unknown chromosome. A comprehensive analysis, including evolutionary, motifs, gene structure, cis-elements, and collinearity was performed to identify VabZIP members. The subcellular localization results showed VabZIPs might locate on the nuclear. Quantitative real-time PCR (qRT-PCR) analysis of the relative expression of VabZIPs in different tissues at the bud stage revealed that VabZIPs had a tissue-specific expression pattern, and its expression was influenced by abiotic stress. These characteristics of VabZIPs provide insights for future research aimed at developing interventions to improve abiotic stress resistance.

S1-bZIP Transcription Factors Play Important Roles in the Regulation of Fruit Quality and Stress Response

Sugar metabolism not only determines fruit sweetness and quality but also acts as signaling molecules to substantially connect with other primary metabolic processes and, therefore, modulates plant growth and development, fruit ripening, and stress response. The basic region/leucine zipper motif (bZIP) transcription factor family is ubiquitous in eukaryotes and plays a diverse array of biological functions in plants. Among the bZIP family members, the smallest bZIP subgroup, S1-bZIP, is a unique one, due to the conserved upstream open reading frames (uORFs) in the 5' leader region of their mRNA. The translated small peptides from these uORFs are suggested to mediate Sucrose-Induced Repression of Translation (SIRT), an important mechanism to maintain sucrose homeostasis in plants. Here, we review recent research on the evolution, sequence features, and biological functions of this bZIP subgroup. S1-bZIPs play important roles in fruit quality, abiotic and biotic stress responses, plant growth and development, and other metabolite biosynthesis by acting as signaling hubs through dimerization with the subgroup C-bZIPs and other cofactors like SnRK1 to coordinate the expression of downstream genes. Direction for further research and genetic engineering of S1-bZIPs in plants is suggested for the improvement of quality and safety traits of fruit.

CaASR1 promotes salicylic acid- but represses jasmonic acid-dependent signaling to enhance the resistance of Capsicum annuum to bacterial wilt by modulating CabZIP63

CabZIP63 acts positively in the resistance of pepper (Capsicum annuum) to bacterial wilt caused by Ralstonia solanacearum or tolerance to high-temperature/high-humidity stress, but it is unclear how CabZIP63 achieves its functional specificity against R. solanacearum. Here, CaASR1, an abscisic acid-, stress-, and ripening-inducible protein of C. annuum, was functionally characterized in modulating the functional specificity of CabZIP63 during the defense response of pepper to R. solanacearum. In pepper plants inoculated with R. solanacearum, CaASR1 was up-regulated before 24 h post-inoculation but down-regulated thereafter, and was down-regulated by high-temperature/high-humidity stress. Data from gene silencing and transient overexpression experiments indicated that CaASR1 acts as a positive regulator in the immunity of pepper against R. solanacearum and a negative regulator of thermotolerance. Pull-down combined with mass spectrometry revealed that CaASR1 interacted with CabZIP63 upon R. solanacearum infection; the interaction was confirmed by microscale thermophoresis and bimolecular fluorescence complementation assays.CaASR1 silencing upon R. solanacearum inoculation repressed CabZIP63-mediated transcription from the promoters of the salicylic acid (SA)-dependent CaPR1 and CaNPR1, but derepressed transcription of CaHSP24 and the jasmonic acid (JA)-dependent CaDEF1. Our findings suggest that CaASR1 acts as a positive regulator of the defense response of pepper to R. solanacearum by interacting with CabZIP63, enabling it to promote SA-dependent but repress JA-dependent immunity and thermotolerance during the early stages of infection.

Comprehensive transcriptome resource for response to phytohormone-induced signaling in Capsicum annuum L

OBJECTIVES

Phytohormones are small signaling molecules with crucial roles in plant growth, development, and environmental adaptation to biotic and abiotic stress responses. Despite several previously published molecular studies focused on plant hormones, our understanding of the transcriptome induced by phytohormones remains unclear, especially in major crops. Here, we aimed to provide transcriptome dataset using RNA sequencing for phytohormone-induced signaling in plant.

DATA DESCRIPTION

We used high-throughput RNA sequencing profiling to investigate the pepper plant response to treatment with four major phytohormones (salicylic acid, jasmonic acid, ethylene, and abscisic acid). This dataset yielded 78 samples containing three biological replicates per six different time points for each treatment and the control, constituting 187.8 Gb of transcriptome data (2.4 Gb of each sample). This comprehensive parallel transcriptome data provides valuable information for understanding the relationships and molecular networks that regulate the expression of phytohormone-related genes involved in plant developments and environmental stress adaptation.

Genome-Wide Identification and Expression Analysis of the Strawberry FvbZIP Gene Family and the Role of Key Gene FabZIP46 in Fruit Resistance to Gray Mold

A total of 54 FvbZIP genes were identified from the strawberry genome. These genes were found to be unevenly distributed on seven different chromosomes, and two of the genes had no matching chromosomal localization. FvbZIP genes were divided into 10 subfamilies according to protein sequence, and the structures of these genes were found to be highly conserved. Based on the bioinformatics analysis of FvbZIP genes, the expression of FabZIP genes changed during different stages of its growth and of its infection with gray mold disease. FabZIP46 was substantially upregulated, and its expression remained relatively high. FabZIP46 was cloned from cultivated strawberries by homologous cloning. The results of a transient transgenic assay revealed that the damage to the fruit tissue was markedly alleviated in strawberries overexpressing FabZIP46, with the incidence rate being substantially lower than that in the control group. By contrast, a brief silencing of FabZIP46 had the opposite effect. The results revealed that FabZIP46 played a positive role in the resistance of strawberries to Botrytis cinerea. The study findings provide valuable insights into the role of bZIP transcription factors as well as a theoretical reference for the regulation of resistance to gray mold disease in strawberry fruit.

Characterization of the bZIP Transcription Factor Family in Pepper (Capsicum annuum L.): CabZIP25 Positively Modulates the Salt Tolerance

The basic leucine zipper (bZIP) proteins compose a family of transcription factors (TFs), which play a crucial role in plant growth, development, and abiotic and biotic stress responses. However, no comprehensive analysis of bZIP family has been reported in pepper (Capsicum annuum L.). In this study, we identified and characterized 60 bZIP TF-encoding genes from two pepper genomes. These genes were divided into 10 groups based on their phylogenetic relationships with bZIP genes from Arabidopsis. Six introns/exons structural patterns within the basic and hinge regions and the conserved motifs were identified among all the pepper bZIP proteins, on the basis of which, we classify them into different subfamilies. Based on the transcriptomic data of Zunla-1 genome, expression analyses of 59 pepper bZIP genes (not including CabZIP25 of CM334 genome), indicated that the pepper bZIP genes were differentially expressed in the pepper tissues and developmental stages, and many of the pepper bZIP genes might be involved in responses to various abiotic stresses and phytohormones. Further, gene expression analysis, using quantitative real-time PCR (qRT-PCR), showed that the CabZIP25 gene was expressed at relatively higher levels in vegetative tissues, and was strongly induced by abiotic stresses and phytohormones. In comparing with wild type Arabidopsis, germination rate, fresh weight, chlorophyll content, and root lengths increased in the CabZIP25-overexpressing Arabidopsis under salt stress. Additionally, CabZIP25-silenced pepper showed lower chlorophyll content than the control plants under salt stress. These results suggested that CabZIP25 improved salt tolerance in plants. Taken together, our results provide new opportunities for the functional characterization of bZIP TFs in pepper.

Silencing of an α-dioxygenase gene, Ca-DOX, retards growth and suppresses basal disease resistance responses in Capsicum annum

Alpha-dioxygenases (α-DOX) catalyzing the primary oxygenation of fatty acids to oxylipins were recently found in plants. Here, the biological roles of the pepper α-DOX (Ca-DOX) gene, which is strongly induced during non-host pathogen infection in chili pepper, were examined. Virus-induced gene silencing demonstrated that down-regulation of Ca-DOX enhanced susceptibility to bacterial pathogens and suppressed the hypersensitive response via the suppression of pathogenesis-related genes such as PR4, proteinase inhibitor II and lipid transfer protein (PR14). Ca-DOX-silenced pepper plants also exhibited more retarded growth with lower epidermal cell numbers and reduced cell wall thickness than control plants. To better understand regulation of Ca-DOX, transgenic Arabidopsis plants harboring the β-glucuronidase (GUS) reporter gene driven from a putative Ca-DOX promoter were generated. GUS expression was significantly induced upon avirulent pathogen infection in transgenic Arabidopsis leaves, whereas GUS induction was relatively weak upon virulent pathogen treatment. After treatment with plant hormones, early and strong GUS expression was seen after treatment of salicylic acid, whereas ethylene and methyl jasmonate treatments produced relatively weak and late GUS signals. These results will enable us to further understand the role of α-DOX, which is important in lipid metabolism, defense responses, and growth development in plants.

Differential expression of four soybean bZIP genes during Phakopsora pachyrhizi infection

Asian soybean rust (ASR), caused by the obligate biotrophic fungus Phakopsora pachyrhizi, is one of most important diseases in the soybean (Glycine max (L.) Merr.) agribusiness. The identification and characterization of genes related to plant defense responses to fungal infection are essential to develop ASR-resistant plants. In this work, we describe four soybean genes, GmbZIP62, GmbZIP105, GmbZIPE1, and GmbZIPE2, which encode transcription factors containing a basic leucine zipper (bZIP) domain from two divergent classes, and that are responsive to P. pachyrhizi infection. Molecular phylogenetic analyses demonstrated that these genes encode proteins similar to bZIP factors responsive to pathogens. Yeast transactivation assays showed that only GmbZIP62 has strong transactivation activity in yeast. In addition, three of the bZIP transcription factors analyzed were also differentially expressed by plant defense hormones, and all were differentially expressed by fungal attack, indicating that these proteins might participate in response to ASR infection. The results suggested that these bZIP proteins are part of the plant defense response to P. pachyrhizi infection, by regulating the gene expression related to ASR infection responses. These bZIP genes are potential targets to obtain new soybean genotypes resistant to ASR.

Pepper, chili (Capsicum annuum)

Pepper is a recalcitrant plant for Agrobacterium-mediated genetic transformation. Several obstacles to genetic transformation remain such as extremely low transformation rates; the choice of correct genotype is critical; and there is a high frequency of false positives due to direct shoot formation. Here, we report a useful protocol with a suitable selection method. The most important aspect of the pepper transformation protocol is selecting shoots growing from the callus, which is referred to as callus-mediated shoot formation. This protocol is a reproducible and reliable system for pepper transformation.

Pathogenesis-related protein 4b interacts with leucine-rich repeat protein 1 to suppress PR4b-triggered cell death and defense response in pepper

To control defense and cell-death signaling, plants contain an abundance of pathogen recognition receptors such as leucine-rich repeat (LRR) proteins. Here we show that pepper (Capsicum annuum) LRR1 interacts with the pepper pathogenesis-related (PR) protein 4b, PR4b, in yeast and in planta. PR4b is synthesized in the endoplasmic reticulum, interacts with LRR1 in the plasma membrane, and is secreted to the apoplast via the plasma membrane. Binding of PR4b to LRR1 requires the chitin-binding domain of PR4b. Purified PR4b protein inhibits spore germination and mycelial growth of plant fungal pathogens. Transient expression of PR4b triggers hypersensitive cell death. This cell death is compromised by co-expression of LRR1 as a negative regulator in Nicotiana benthamiana leaves. LRR1/PR4b silencing in pepper and PR4b over-expression in Arabidopsis thaliana demonstrated that LRR1 and PR4b are necessary for defense responses to Pseudomonas syringae pv. tomato and Hyaloperonospora arabidopsidis (Hpa) infection. The mutant of the PR4b Arabidopsis ortholog, pr4, showed enhanced susceptibility to Hpa infection. Together, our results suggest that PR4b functions as a positive modulator of plant cell death and defense responses. However, the activity of PR4b is suppressed by interaction with LRR1.

Plant bZIP transcription factors responsive to pathogens: a review

Transcription factors of the basic leucine zipper (bZIP) family control important processes in all eukaryotes. In plants, bZIPs are master regulators of many central developmental and physiological processes, including morphogenesis, seed formation, abiotic and biotic stress responses. Modulation of the expression patterns of bZIP genes and changes in their activity often contribute to the activation of various signaling pathways and regulatory networks of different physiological processes. However, most advances in the study of plant bZIP transcription factors are related to their involvement in abiotic stress and development. In contrast, there are few examples of functional research with regard to biotic stress, particularly in the defense against pathogens. In this review, we summarize the recent progress revealing the role of bZIP transcription factors in the biotic stress responses of several plant species, from Arabidopsis to cotton. Moreover, we summarize the interacting partners of bZIP proteins in molecular responses during pathogen attack and the key components of the signal transduction pathways with which they physically interact during plant defense responses. Lastly, we focus on the recent advances regarding research on the functional role of bZIPs in major agricultural cultivars and examine the studies performed in this field.

CaMsrB2, pepper methionine sulfoxide reductase B2, is a novel defense regulator against oxidative stress and pathogen attack

Reactive oxygen species (ROS) are inevitably generated in aerobic organisms as by-products of normal metabolism or as the result of defense and development. ROS readily oxidize methionine (Met) residues in proteins/peptides to form Met-R-sulfoxide or Met-S-sulfoxide, causing inactivation or malfunction of the proteins. A pepper (Capsicum annuum) methionine sulfoxide reductase B2 gene (CaMsrB2) was isolated, and its roles in plant defense were studied. CaMsrB2 was down-regulated upon inoculation with either incompatible or compatible pathogens. The down-regulation, however, was restored to the original expression levels only in a compatible interaction. Gain-of-function studies using tomato (Solanum lycopersicum) plants transformed with CaMsrB2 resulted in enhanced resistance to Phytophthora capsici and Phytophthora infestans. Inversely, loss-of-function studies of CaMsrB2 using virus-induced gene silencing in pepper plants (cv Early Calwonder-30R) resulted in accelerated cell death from an incompatible bacterial pathogen, Xanthomonas axonopodis pv vesicatoria (Xav) race 1, and enhanced susceptibility to a compatible bacterial pathogen, virulent X. axonopodis pv vesicatoria race 3. Measurement of ROS levels in CaMsrB2-silenced pepper plants revealed that suppression of CaMsrB2 increased the production of ROS, which in turn resulted in the acceleration of cell death via accumulation of ROS. In contrast, the CaMsrB2-transgenic tomato plants showed reduced production of hydrogen peroxide. Taken together, our results suggest that the plant MsrBs have novel functions in active defense against pathogens via the regulation of cell redox status.

Analysis of floral transcription factors from Lycoris longituba

Transcription factors (TFs) are proteins that bind to specific promoter regions of their target genes and regulate gene transcription. Many of these factors have been found to influence flowering. Lycoris longituba exhibits a great deal of diversity in flower color and flower form, making it a suitable model for the study of floral development. We have identified 338 putative TFs from more than thirty thousand ESTs sequenced from the floral tissue of L. longituba, and validated them using real-time RT-PCR. Fifty-one of the TFs were recognized as being potentially flower-specific, and the expression patterns of some of them during six flowering phases have been elucidated. Homolog annotation and phylogenetic analysis revealed that some TFs that belong to several TF families, such as MADS, MYB-related, NAC, and ABI3-VP1, were suggested to play important roles in the flowering process. Our dataset may be used to identify priority target TF genes for further study.

A novel pepper (Capsicum annuum) receptor-like kinase functions as a negative regulator of plant cell death via accumulation of superoxide anions

Plant receptor-like kinases belong to a large gene family. The Capsicum annuum receptor-like kinase 1 (CaRLK1) gene encodes a transmembrane protein with a cytoplasmic kinase domain and an extracellular domain. The CaRLK1 extracellular domain (ECD)-green fluorescent protein (GFP) fusion protein was targeted to the plasma membrane, and the kinase domain of the CaRLK1 protein exhibited autophosphorylation activity. CaRLK1 transcripts were more strongly induced in treatment with Xag8ra than in treatment with Xag8-13. Furthermore, infection with incompatible Xanthomonas campestris pv. vesicatoria race 3 induced expression of CaRLK1 more strongly than in the compatible interaction. Cell death caused by both a disease-forming and an HR-inducing pathogen was delayed in the CaRLK1-transgenic plants. Ectopic expression of CaRLK1 also induced transcripts of the lesion stimulating disease (LSD) gene, a negative regulator of cell death. Respiratory burst oxidase homolog (RBOH) genes were up-regulated in the transgenic plants compared with the wild type, as the concentration of the superoxide anion was increased. In contrast, the concentration of H(2)O(2) did not differ between the transgenic and wild-type plants. These results support the theory that the suppression of plant cell death by CaRLK1 is associated with consistent production of the superoxide anion and induction of the RBOH genes and the LSD gene, but not with the concentration of H(2)O(2). Thus, CaRLK1 may be a receptor of an as yet unidentified pathogen molecular pattern and may function as a negative regulator of plant cell death.

Patterns of defence gene expression in the tomato–Verticilliuminteraction

In a tomato plant infected by Verticillium dahliae , race 1, compatibility or incompatibility appears to be determined in the stem, but little is known about the genes that either regulate or effect critical cellular events. In the present study, microarray and RT-PCR analyses were used to assess changes in tomato mRNA populations during both interactions. Initially, a commercially available DNA chip was used to screen gene expression at a single critical time point after inoculation of resistant and susceptible plants. From the results, the most-affected genes were selected to develop a tomato Verticillium response (TVR) DNA chip for detailed analyses of gene expression for 15 d after inoculation. Taken together, over half of the genes on the TVR array exhibited one of three distinct patterns of change, one reflecting a resistant phenotype and two being consistent with a susceptible phenotype. Of particular interest was a cluster of strongly expressed genes belonging to groups 2 and 3 that appeared to be co-ordinately down regulated in infected resistant plants relative to susceptible. Many of these genes encode pathogenesis related (PR) proteins. The data demonstrate that even though complex, the biological system can be standardized sufficiently to allow the reproducible analysis of gene expression in a whole plant system and provide patterns of transcriptional variation that can be used to assess the significance of specific genes in pathogenesis and resistance.

Expression patterns within the Arabidopsis C/S1 bZIP transcription factor network: availability of heterodimerization partners controls gene expression during stress response and development

Members of the Arabidopsis group C/S1 basic leucine zipper (bZIP) transcription factor (TF) network are proposed to implement transcriptional reprogramming of plant growth in response to energy deprivation and environmental stresses. The four group C and five group S1 members form specific heterodimers and are, therefore, considered to cooperate functionally. For example, the interplay of C/S1 bZIP TFs in regulating seed maturation genes was analyzed by expression studies and target gene regulation in both protoplasts and transgenic plants. The abundance of the heterodimerization partners significantly affects target gene transcription. Therefore, a detailed analysis of the developmental and stress related expression patterns was performed by comparing promoter: GUS and transcription data. The idea that the C/S1 network plays a role in the allocation of nutrients is supported by the defined and partially overlapping expression patterns in sink leaves, seeds and anthers. Accordingly, metabolic signals strongly affect bZIP expression on the transcriptional and/or post-transcriptional level. Sucrose induced repression of translation (SIRT) was demonstrated for all group S1 bZIPs. In particular, transcription of group S1 genes strongly responds to various abiotic stresses, such as salt (AtbZIP1) or cold (AtbZIP44). In summary, heterodimerization and expression data provide a basic framework to further determine the functional impact of the C/S1 network in regulating the plant energy balance and nutrient allocation.

A novel CaAbsi1 gene induced by early-abiotic stresses in pepper

The full-length cDNA of CaAbsi1 encodes a presumptive protein of 134 amino acid residues that has homology to a putative zinc finger protein in its C-terminus. The deduced amino acid sequence has 50% homology to Oryza sativa NP001049-274, the function of which is unknown. Expression of CaAbsi1 was reduced in response to inoculation of non-host pathogens. On the other hand it was induced one hour after exposure to high concentrations of NaCl or mannitol, and six hours after transfer to low temperature. Induction also occurred in response to oxidative stress, methyl viologen, hydrogen peroxide and abscisic acid. Our results suggest that CaAbsi1 plays a role in multiple responses to wounding and abiotic stresses.

Capsicum annuum WRKY protein CaWRKY1 is a negative regulator of pathogen defense

Plants respond to pathogens by regulating a network of signaling pathways that fine-tune transcriptional activation of defense-related genes. The aim of this study was to determine the role of Capsicum annuum WRKY zinc finger-domain transcription factor 1 (CaWRKY1) in defense. In previous studies, CaWRKY1 was found to be rapidly induced in C. annuum (chili pepper) leaves by incompatible and compatible pathogen inoculations, but the complexity of the network of the WRKY family prevented the function of CaWRKY1 in defense from being elucidated. Virus-induced gene silencing of CaWRKY1 in chili pepper leaves resulted in decreased growth of Xanthomonas axonopodis pv. vesicatoria race 1. CaWRKY1-overexpressing transgenic plants showed accelerated hypersensitive cell death in response to infection with tobacco mosaic virus and Pseudomonas syringe pv. tabaci. Lower levels of pathogenesis-related gene induction were observed in CaWRKY1-overexpressing transgenic plants following salicylic acid (SA) treatments. This work suggests that the newly characterized CaWRKY1, which is strongly induced by pathogen infections and the signal molecule SA, acts as a regulator to turn off systemic acquired resistance once the pathogen challenge has diminished and to prevent spurious activation of defense responses at suboptimal concentrations of SA.

The chili pepper CaATL1: an AT-hook motif-containing transcription factor implicated in defence responses against pathogens

SUMMARY Using cDNA microarray analysis, we isolated a cDNA clone, CaATL1 (Capsicum annuum L. Bukang AT-hook-Like gene 1), from a chili pepper plant incompatibly interacting with bacterial pathogens. The deduced amino acid sequence has a potential nuclear localization sequence and an AT-hook DNA binding motif which can bind AT-rich sequence elements. Expression of CaATL1 was specifically induced in host- and non-host-resistant responses against bacterial and viral pathogens in pepper plants. In addition, CaATL1 transcripts also increased following salicylic acid and ethephone treatment but were only mildly induced by methyl-jasmonate treatment. CaATL1::smGFP (soluble-modified green fluorescent protein) fusion protein localized to nuclei in tobacco BY2 protoplasts. The C-terminal region of the CaATL1 protein fused to the LexA DNA binding domain was able to activate reporter gene expression in yeast. To analyse further the role of the CaATL1 in pathogen defence response, we generated CaATL1-over-expressing transgenic tomato plants. These transgenic plants showed enhanced disease resistance against bacterial and oomycete pathogens. Taken together, these results provide the first evidence of a role for a plant AT-hook motif-containing transcription factor in pathogen defence response.

Retrotransposon and gene activation in wheat in response to mycotoxigenic and non-mycotoxigenic-associated Fusarium stress

Despite inhibition of protein synthesis being its mode of action, the trichothecene mycotoxin deoxynivalenol (DON) induced accumulation of transcripts encoding translation elongation factor 1alpha (EF-1alpha), class III plant peroxidase (POX), structure specific recognition protein, basic leucine zipper protein transcription factor (bZIP), retrotransposon-like homologs and genes of unknown function in the roots of wheat cultivars CM82036 and Remus. Fusarium head blight (FHB) studies using Fusarium graminearum and its trichothecene-minus (Tri5 ( - )) mutant derivative and adult plant DON tests showed that these transcripts were responsive to both mycotoxigenic- and non-mycotoxigenic-associated Fusarium stress. In tests using the parents 'CM82036', 'Remus' and 14 double-haploid progeny that segregated for quantitative trait locus (QTL) Fhb1 on chromosome 3BS (syn. Qfhs.ndsu-3BS) (from 'CM82036' that confers DON tolerance), bZIP expression was significantly more DON-up-regulated in lines that inherited this QTL. Basal accumulation of the bZIP transcript in spikelets treated with Tween20 (control), DON and in DON-relative to Tween20-treated spikelets was negatively correlated with DON-induced bleaching above (but not below) the treated spikelets (AUDPC(DON)) (r = -0.41, -0.75 and -0.72, respectively; P < or = 0.010). bZIP-specific PCR analysis of 'Chinese spring' and its 3BS deletion derivatives indicated that bZIP is located in chromosomal region(s) other than 3BS. These results, and the fact that a homologous cold-regulated wheat bZIP (wLIP19) maps to group 1 chromosomes suggests that wheat bZIP may participate in defence response cascades associated with Fhb1 and that there is a cross-talk between biotic and abiotic stress signalling pathways.

Metallothionein and bZIP Transcription Factor Genes from Velvetleaf and Their Differential Expression Following Colletotrichum coccodes Infection

ABSTRACT Colletotrichum coccodes is a biocontrol agent of velvetleaf (Abutilon theophrasti), a noxious weed of corn and soybean. Metallothioneins (MTs) and basic region/leucine zipper motif (bZIP) are heavy-metal-binding proteins and transcription factors, respectively, that have been related to several plant processes, including the responses of plants to pathogen attack. Previous investigation of the determinants involved in the velvet-leaf-C. coccodes interaction had shed light on particular plant and fungal genes expressed in this pathosystem. Here, we report on the temporal expression patterns of two distinct types (2 and 3) of MT and bZIP transcription factor genes in velvetleaf leaves following infection with C. coccodes using quantitative reverse-transcription polymerase chain reaction. Gene expression ratios were significantly upregulated 1 day after infection (DAI), a time at which velvetleaf leaves appeared symptomless. At 2 DAI, bZIP and type 3 MT expression ratios dropped to levels significantly lower than those estimated for noninfected plants. Necrotic symptoms appeared 5 DAI and increased with time, during which gene expression levels were maintained either below or at levels observed in the control. These findings indicate that C. coccodes altered the expression of type 2 and 3 MT and bZIP genes. In addition, this is the first report on induction of a type 3 MT in plants in response to a pathogen attack.

Expression and functional roles of the pepper pathogen-induced transcription factor RAV1 in bacterial disease resistance, and drought and salt stress tolerance

A novel pathogen-induced gene encoding the RAV (Related to ABI3/VP1) transcription factor, CARAV1, was isolated from pepper leaves infected with Xanthomonas campestris pv. vesicatoria. CARAV1 contains two distinct DNA-binding domains AP2 and B3 uniquely found in higher plants. Transient expression analysis of the smGFP:CARAV1 fusion construct in Arabidopsis protoplasts and pepper epidermal cells revealed the CARAV1 protein to be localized in the nucleus. The N-terminal region of CARAV1 fused to the GAL4 DNA-binding domain was required to activate transcription of reporter genes in yeast. In yeast one-hybrid, the recognition of CAACA and CACCTG motifs also were essential for the CARAV1 protein to bind to a specific target gene and activate the reporter gene. The expression of the CARAV1 gene was strongly induced early in pepper leaves during the pathogen infection, abiotic elicitors and environmental stresses. CARAV1 transcripts were localized in the phloem cells of leaf tissues during pathogen infection and ethylene treatment. Ectopic expression of the CARAV1 gene in transgenic Arabidopsis plants induced some PR genes and enhanced resistance against infection by Pseudomonas syringae pv. tomato DC3000 and osmotic stresses by high salinity and dehydration. The CARAV1 promoter activation was induced by P. syringae pv. tabaci, salicylic acid and abscisic acid. These data suggest that pathogen- and abiotic stress-inducible CARAV1 functions as a transcriptional activator triggering resistance to bacterial infection and tolerance to osmotic stresses.

Suppression of CaCYP1, a novel cytochrome P450 gene, compromises the basal pathogen defense response of pepper plants

A putative cytochrome P450 gene from chili pepper, Capsicum annuum L. Bukang cytochrome P450 (CaCYP1), was identified using cDNA microarray analysis of gene expression following induction of the leaf hypersensitive response by inoculation of pepper plants with the non-host pathogen Xanthomonas axonopodis pv. glycines 8ra. The full-length cDNA of CaCYP1 encoded a protein of 514 amino acid residues, which contained a putative hydrophobic membrane anchoring domain in the N-terminal region, and a heme-binding motif in the C-terminal region. Analysis of the deduced amino acid sequence of CaCYP1 revealed that it has high homology to Arabidopsis CYP89A5, the function of which is unknown. Expression of CaCYP1 was preferentially increased in pepper plants in response to non-host pathogen inoculation and also during the host resistance response. CaCYP1 expression also increased following treatment with salicylic acid and abscisic acid, while treatment with ethylene had a mild effect. Using a virus-induced gene silencing-based reverse genetics approach, we demonstrated that suppression of CaCYP1 results in enhanced susceptibility to bacterial pathogens. Interestingly, gene silencing of CaCYP1 in pepper plants resulted in the reduced expression of the defense-related genes CaLTP1, CaSIG4, and Cadhn. Our results indicated that CaCYP1, a novel cytochrome P450 in pepper plants, may play a role in plant defense response pathways that involve salicylic acid and abscisic acid signaling pathways.

Expression of a novel NAC domain-containing transcription factor (CaNAC1) is preferentially associated with incompatible interactions between chili pepper and pathogens

We aim to isolate genes in chili pepper that are regulated during the hypersensitive response to infection by nonhost pathogens, with a view to elucidating the defense responses against pathogen attack. Among the 90 transcription factors initially characterized by reverse RNA gel blot analysis, a cDNA clone, CaNAC1 (Capsicum annuum NAC1) containing the plant-specific NAC domain motif was further characterized. Expression of the CaNAC1 gene was rapidly and specifically induced during incompatible interactions between pepper and bacterial or viral pathogens. Additionally, this gene was strongly induced by exogenously applied salicylic acid and ethephon, whereas methyl jasmonate only had a transient effect. A CaNAC1-smGFP (soluble modified green fluorescent protein) fusion protein localized to the nucleus following transfection into the epidermis of onion. Using the yeast system, we further disclose that the transcription activation domain of CaNAC1 is located in the C-terminal half of the protein. Our results collectively suggest that the plant-specific NAC domain protein, CaNAC1, may play a role in the regulation of defense responses in plants.

Identification of a CaRAV1 possessing an AP2/ERF and B3 DNA-binding domain from pepper leaves infected with Xanthomonas axonopodis pv. glycines 8ra by differential display

We isolated a cDNA clone, CaRAV1, which exhibited significant similarity to those of Arabidopsis RAV proteins containing AP2/ERF and B3-like DNA-binding domains. CaRAV1 expression was rapidly and specifically induced in both host and non-host resistant responses against bacterial pathogens in the chili pepper plant. CaRAV1 also strongly increased following salicylic acid and ethephon treatments, whereas methyl-jasmonate only had mild effects. Furthermore, CaRAV1 transcript levels were also investigated in response to ABA and abiotic stress. No significant CaRAV1 expression was evident following ABA, mannitol, or cold treatments. These observations collectively provide initial evidence that the pepper RAV transcription factor homolog may function in plant defense responses.

Sucrose-induced translational repression of plant bZIP-type transcription factors

Sugars as signalling molecules exert control on the transcription of many plant genes. Sugar signals also alter mRNA and protein stability. Increased sucrose concentrations specifically repress translation of the S-class basic region leucine zipper (bZIP) type transcription factor AtbZIP11/ATB2. This sucrose-induced repression of translation (SIRT) depends on translation of a highly conserved upstream open reading frame (uORF) in the 5' UTR of the gene. This conserved uORF is exclusively encoded in 5' UTRs of several plant S-class bZIP transcription factors. Arabidopsis homologues of ATB2/AtbZIP11, which harbour the conserved uORF, also show SIRT. Therefore, SIRT emerges as a general sucrose translational control mechanism of a group of transcription factors. SIRT might be part of a sucrose-specific signalling pathway, controlling expression of plant bZIP transcription factor genes.

A plant EPF-type zinc-finger protein, CaPIF1, involved in defence against pathogens

SUMMARY To understand better the defence responses of plants to pathogen attack, we challenged hot pepper plants with bacterial pathogens and identified transcription factor-encoding genes whose expression patterns were altered during the subsequent hypersensitive response. One of these genes, CaPIF1 (Capsicum annuum Pathogen-Induced Factor 1), was characterized further. This gene encodes a plant-specific EPF-type protein that contains two Cys(2)/His(2) zinc fingers. CaPIF1 expression was rapidly and specifically induced when pepper plants were challenged with bacterial pathogens to which they are resistant. In contrast, challenge with a pathogen to which the plants are susceptible only generated weak CaPIF1 expression. CaPIF1 expression was also strongly induced in pepper leaves by the exogenous application of ethephon, an ethylene-releasing compound, and salicylic acid, whereas methyl jasmonate had only moderate effects. CaPIF1 localized to the nuclei of onion epidermis when expressed as a CaPIF1-smGFP fusion protein. Transgenic tobacco plants over-expressing CaPIF1 driven by the CaMV 35S promoter showed increased resistance to challenge with a tobacco-specific pathogen or non-host bacterial pathogens. These plants also showed constitutive up-regulation of multiple defence-related genes. Moreover, virus-induced silencing of the CaPIF1 orthologue in Nicotiana benthamiana enhanced susceptibility to the same host or non-host bacterial pathogens. These observations provide evidence that an EPF-type Cys(2)/His(2) zinc-finger protein plays a crucial role in the activation of the pathogen defence response in plants.

The pepper transcription factor CaPF1 confers pathogen and freezing tolerance in Arabidopsis

An ERF/AP2-type transcription factor (CaPF1) was isolated by differential-display reverse transcription-PCR, following inoculation of the soybean pustule pathogen Xanthomonas axonopodis pv glycines 8ra, which induces hypersensitive response in pepper (Capsicum annuum) leaves. CaPF1 mRNA was induced under conditions of biotic and abiotic stress. Higher levels of CaPF1 transcripts were observed in disease-resistant tissue compared with susceptible tissue. CaPF1 expression was additionally induced using various treatment regimes, including ethephon, methyl jasmonate, and cold stress. To determine the role of CaPF1 in plants, transgenic Arabidopsis and tobacco (Nicotiana tabacum) plants expressing higher levels of CaPF1 were generated. Gene expression analyses of transgenic Arabidopsis and tobacco revealed that the CaPF1 level in transgenic plants affects expression of genes that contain either a GCC or a CRT/DRE box in their promoter regions. Furthermore, transgenic Arabidopsis plants expressing CaPF1 displayed tolerance against freezing temperatures and enhanced resistance to Pseudomonas syringae pv tomato DC3000. Disease tolerance was additionally observed in CaPF1 transgenic tobacco plants. The results collectively indicate that CaPF1 is an ERF/AP2 transcription factor in hot pepper plants that may play dual roles in response to biotic and abiotic stress in plants.

A conserved upstream open reading frame mediates sucrose-induced repression of translation

Sugars have been shown to regulate transcription of numerous genes in plants. Sucrose controls translation of the group S basic region leucine zipper (bZIP)-type transcription factor ATB2/AtbZIP11 (Rook et al., 1998a). This control requires the unusually long 5' untranslated region (UTR) of the gene. Point mutations and deletions of the 5'UTR have uncovered the sequences involved. A highly conserved upstream open reading frame (uORF) coding for 42 amino acids is essential for the repression mechanism. It is conserved in 5'UTRs of bZIP transcription factors from other Arabidopsis thaliana genes and many other plants. ATB2/AtbZIP11 is normally expressed in association with vascular tissues. Ectopic expression of a 5'UTR construct shows that the sucrose repression system is functional in all tissues. AtbZIP2 is another Arabidopsis bZIP transcription factor gene harboring the conserved uORF, which is regulated similarly via sucrose-induced repression of translation. This suggests a general function of the conserved uORF in sucrose-controlled regulation of expression. Our findings imply the operation of a sucrose-sensing pathway that controls translation of several plant bZIP transcription factor genes harboring the conserved uORF in their 5'UTRs. Target genes of such transcription factors will then be regulated in sucrose-dependent way.

EST and microarray analyses of pathogen-responsive genes in hot pepper (Capsicum annuum L.) non-host resistance against soybean pustule pathogen (Xanthomonas axonopodis pv. glycines)

Large-scale single-pass sequencing of cDNA libraries and microarray analysis have proven to be useful tools for discovering new genes and studying gene expression. As a first step in elucidating the defense mechanisms in hot pepper plants, a total of 8,525 expressed sequence tags (ESTs) were generated and analyzed in silico. The cDNA microarray analysis identified 613 hot pepper genes that were transcriptionally responsive to the non-host soybean pustule pathogen Xanthomonas axonopodis pv. glycines ( Xag). Several functional types of genes, including those involved in cell wall modification/biosynthesis, transport, signaling pathways and divergent defense reactions, were induced at the early stage of Xag infiltration. In contrast, genes encoding proteins that are involved in photosynthesis, carbohydrate metabolism and the synthesis of chloroplast biogenetic proteins were down-regulated at the late stage of Xag infiltration. These expression profiles share common features with the expression profiles elicited by other stresses, such as fungal challenge, wounding, cold, drought and high salinity. However, we also identified several novel transcription factors that may be specifically involved in the defense reaction of the hot pepper. We also found that the defense reaction of the hot pepper may involve the deactivation of gibberellin. Furthermore, many genes encoding proteins with unknown function were identified. Functional analysis of these genes may broaden our understanding of non-host resistance. This study is the first report of large-scale sequencing and non-host defense transcriptome analysis of the hot pepper plant species. (The sequence data in this paper have been submitted to the dbEST and GenBank database under the codes 10227604-10236595 and BM059564-BM068555, respectively. Additional information is available at http://plant.pdrc.re.kr/ks200201/pepper.html).