Overexpression of the AP2/EREBP transcription factor OPBP1 enhances disease resistance and salt tolerance in tobacco

Citrus transcription factor CsERF1 is involved in the response to citrus tristeza disease

Introduction

Citrus tristeza virus (CTV) is a threat to the citrus production and causes severe economic losses to the citrus industry. Ethylene response factors (ERFs) play important roles in plant growth and stress responses. Although ERF genes have been widely studied in model plants, little is known about their role in biological stress responses in fruit trees, such as citrus. CsERF1 belongs to the citrus AP2/ERF transcription factor family.

Methods

To determine the role of CsERF1 on CTV resistance in citrus and the effects of the exongenous hormone application on CsERF1 in citrus, the expression of related genes was quantitatively analyzed by quantitative reverse transcription polymerase chain reaction (RT-qPCR) in this study.

Results

The expression profile showed that the expression level of CsERF1 in roots was significantly lower under CTV infection than in healthy plants, while the expression level in stems was significantly increased. CsERF1 responded to exogenous salicylic acid (SA) and methyl jasmonate (MeJA) treatments. The CTV titer in RNAi-CsERF1 transgenic sweet orange plants significantly increased. Furthermore, CsERF1-overexpressing and RNAi-CsERF1 transgenic sweet orange plants exhibited differential expression of genes involved in jasmonic acid (JA) and SA signaling.

Discussion

These results suggest that CsERF1 mediates CTV resistance by regulating the JA and SA signaling pathways. The results of this study provide new clues as to the citrus defence response against CTV. It is of great significance to create citrus germplasm resources resistant to recession disease.

G-Quadruplex Structures as Epigenetic Regulatory Elements in Priming of Defense Genes upon Short-Term Trichoderma atroviride Inoculation in Maize

Symbiosis establishment between Trichoderma atroviride and plant roots triggers the priming of defense responses, among other effects. Currently, there is no clear evidence regarding the molecular mechanisms that allow the plant to remain alert to future stimulus, either by pathogen attack or any other abiotic stress. Epigenetic modifications have emerged as a strategy to explain the increased defense response of plants in a priming state conferred by Trichoderma. Recently, various non-canonical structures of nucleic acids, especially G-quadruplex structures (G-quadruplexes or G4s), have been identified as potential targets during the establishment or maintenance of plant signals. In the present study, we developed a screening test for the identification of putative G4-forming sequences (PQSs) in previously identified Z. mays priming genes. Bioinformatic analysis revealed the presence of PQSs in the promoter region of five essential genes playing a critical role in priming in maize. Biophysical and spectroscopy studies showed the formation of G4s by these PQSs in vitro, and ChIP assays demonstrate their formation in vivo. Therefore, G4 formation could play a role as an epigenetic regulatory mechanism involved in the long-lasting primed state in maize plants.

Ethylene-MPK8-ERF.C1-PR module confers resistance against Botrytis cinerea in tomato fruit without compromising ripening

The plant hormone ethylene plays a critical role in fruit defense against Botrytis cinerea attack, but the underlying mechanisms remain poorly understood. Here, we showed that ethylene response factor SlERF.C1 acts as a key regulator to trigger the ethylene-mediated defense against B. cinerea in tomato fruits without compromising ripening. Knockout of SlERF.C1 increased fruit susceptibility to B. cinerea with no effect on ripening process, while overexpression enhanced resistance. RNA-Seq, transactivation assays, EMSA and ChIP-qPCR results indicated that SlERF.C1 activated the transcription of PR genes by binding to their promoters. Moreover, SlERF.C1 interacted with the mitogen-activated protein kinase SlMPK8 which allowed SlMPK8 to phosphorylate SlERF.C1 at the Ser174 residue and increases its transcriptional activity. Knocking out of SlMPK8 increased fruit susceptibility to B. cinerea, whereas overexpression enhanced resistance without affecting ripening. Furthermore, genetic crosses between SlMPK8-KO and SlERF.C1-OE lines reduced the resistance to B. cinerea attack in SlERF.C1-OE fruits. In addition, B. cinerea infection induced ethylene production which in turn triggered SlMPK8 transcription and enhanced the phosphorylation of SlERF.C1. Overall, our findings reveal the regulatory mechanism of the 'Ethylene-MPK8-ERF.C1-PR' module in resistance against B. cinerea and provide new insight into the manipulation of gray mold disease in fruits.

Knockout of CAFFEOYL-COA 3-O-METHYLTRANSFERASE 6/6L enhances the S/G ratio of lignin monomers and disease resistance in Nicotiana tabacum

Background

Nicotiana tabacum is an important economic crop, which is widely planted in the world. Lignin is very important for maintaining the physiological and stress-resistant functions of tobacco. However, higher lignin content will produce lignin gas, which is not conducive to the formation of tobacco quality. To date, how to precisely fine-tune lignin content or composition remains unclear.

Results

Here, we annotated and screened 14 CCoAOMTs in Nicotiana tabacum and obtained homozygous double mutants of CCoAOMT6 and CCoAOMT6L through CRSIPR/Cas9 technology. The phenotype showed that the double mutants have better growth than the wild type whereas the S/G ratio increased and the total sugar decreased. Resistance against the pathogen test and the extract inhibition test showed that the transgenic tobacco has stronger resistance to tobacco bacterial wilt and brown spot disease, which are infected by Ralstonia solanacearum and Alternaria alternata, respectively. The combined analysis of metabolome and transcriptome in the leaves and roots suggested that the changes of phenylpropane and terpene metabolism are mainly responsible for these phenotypes. Furthermore, the molecular docking indicated that the upregulated metabolites, such as soyasaponin Bb, improve the disease resistance due to highly stable binding with tyrosyl-tRNA synthetase targets in Ralstonia solanacearum and Alternaria alternata.

Conclusions

CAFFEOYL-COA 3-O-METHYLTRANSFERASE 6/6L can regulate the S/G ratio of lignin monomers and may affect tobacco bacterial wilt and brown spot disease resistance by disturbing phenylpropane and terpene metabolism in leaves and roots of Nicotiana tabacum, such as soyasaponin Bb.

GmABR1 encoding an ERF transcription factor enhances the tolerance to aluminum stress in Arabidopsis thaliana

The ethylene response factor (ERF) transcription factors, which is one of the largest transcription factor families in plants, are involved in biological and abiotic stress response and play an important role in plant growth and development. In this study, the GmABR1 gene from the soybean inbred line Zhonghuang24 (ZH24)×Huaxia 3 (HX3) was investigated its aluminum (Al) tolerance. GmABR1 protein has a conserved domain AP2, which is located in the nucleus and has transcriptional activation ability. The results of real-time quantitative PCR (qRT-PCR) showed that the GmABR1 gene presented a constitutive expression pattern rich in the root tip, stem and leaf tissues of HX3. After Al stress, the GmABR1 transcript was significantly increased in the roots. The transcripts of GmABR1 in the roots of HX3 treated with 50 µM AlCl₃ was 51 times than that of the control. The GmABR1 was spatiotemporally specific with the highest expression levels when Al concentration was 50 µM, which was about 36 times than that of the control. The results of hematoxylin staining showed that the root tips of GmABR1-overexpression lines were stained the lightest, followed by the control, and the root tips of GmABR1 RNAi lines were stained the darkest. The concentrations of Al³⁺ in root tips were 207.40 µg/g, 147.74 µg/g and 330.65 µg/g in wild type (WT), overexpressed lines and RNAi lines, respectively. When AlCl₃ (pH4.5) concentration was 100 µM, all the roots of Arabidopsis were significantly inhibited. The taproot elongation of WT, GmABR1 transgenic lines was 69.6%, 85.6%, respectively. When treated with Al, the content of malondialdehyde (MDA) in leaves of WT increased to 3.03 µg/g, while that of transgenic Arabidopsis increased from 1.66-2.21 µg/g, which was lower than that of WT. Under the Al stress, the Al stress responsive genes such as AtALMT1 and AtMATE, and the genes related to ABA pathway such as AtABI1, AtRD22 and AtRD29A were up-regulated. The results indicated that GmABR1 may jointly regulate plant resistance to Al stress through genes related to Al stress response and ABA response pathways.

The regulation of Alternaria alternata resistance by LRR-RK4 through ERF109, defensin19 and phytoalexin scopoletin in Nicotiana attenuata

Leucine-rich repeat receptor-like kinases (LRR-RKs), belonging to the largest subfamily of transmembrane receptor-like kinases in plants, are proposed to be involved in pathogen resistance. However, it is currently unknown whether LRR-RKs regulate Nicotiana attenuata resistance to Alternaria alternata, a notorious fungal pathogen causing tobacco brown disease. During transcriptome analysis, we identified a highly induced receptor kinase (NaLRR-RK4) in N. attenuata leaves after A. alternata inoculation. We speculated that this NaLRR-RK4 might be the resistance gene of tobacco to brown spot disease, and if so, what is its function and mechanism of action? Silencing of NaLRR-RK4 via virus-induced gene silencing (VIGS) lead to plants highly susceptible to A. alternata, and this result was further confirmed by two stable transformation lines (NaLRR-RK4-RNAi lines) generated by RNA interference technology. The susceptible of NaLRR-RK4-RNAi lines to A. alternata was associated with reduced levels of phytoalexin scopoletin and its key synthesis gene NaF6'H1. Further transcriptome analysis of leaves of WT and NaLRR-RK4-RNAi line after A. alternata inoculation revealed that NaLRR-RK4 regulated NaERF109 and NaDEF19. Silencing NaERF109 or NaDEF19 by VIGS lead to plants more susceptible to A.alternata, demonstrating their role in pathogen resistance. Interestingly, A.alternata-induced expression of NaF6'H1 and NaDEF19 were dramatically reduced in NaERF109-silenced VIGS plants. Taken all together, we identified LRR-RK4 as the first Leucine-rich repeat receptor-like kinases involved in A.alternata resistance in tobacco species, by regulating NaERF109, and subsequently NaDEF19 and NaF6'H1.

Cell death signalling is competitively but coordinately regulated by repressor-type and activator-type ethylene response factors in tobacco (Nicotiana tabacum) plants

Ethylene response factors (ERFs) comprise one of the largest transcription factor families in many plant species. Tobacco (Nicotiana tabacum) ERF3 (NtERF3) and other ERF-associated amphiphilic repression (EAR) motif-containing ERFs are known to function as transcriptional repressors. NtERF3 and several repressor-type ERFs induce cell death in tobacco leaves and are also associated with a defence response against tobacco mosaic virus (TMV). We investigated whether transcriptional activator-type NtERFs function together with NtERF3 in the defence response against TMV infection by performing transient ectopic expression, together with gene expression, chromatin immunoprecipitation (ChIP) and promoter analyses. Transient overexpression of NtERF2 and NtERF4 induced cell death in tobacco leaves, albeit later than that induced by NtERF3. Fusion of the EAR motif to the C-terminal end of NtERF2 and NtERF4 abolished their cell death-inducing ability. The expression of NtERF2 and NtERF4 was upregulated at the early phase of N gene-triggered hypersensitive response (HR) against TMV infection. The cell death phenotype induced by overexpression of wild-type NtERF2 and NtERF4 was suppressed by co-expression of an EAR motif-deficient form of NtERF3. Furthermore, ChIP and promoter analyses suggested that NtERF2, NtERF3 and NtERF4 positively or negatively regulate the expression of NtERF3 by binding to its promoter region. Overall, our results revealed the cell death-inducing abilities of genes encoding activator-type NtERFs, including NtERF2 and NtERF4, suggesting that the HR-cell death signalling via the repressor-type NtERF3 is competitively but coordinately regulated by these NtERFs.

Effects of Combined Abiotic Stresses Related to Climate Change on Root Growth in Crops

Climate change is a major threat to crop productivity that negatively affects food security worldwide. Increase in global temperatures are usually accompanied by drought, flooding and changes in soil nutrients composition that dramatically reduced crop yields. Against the backdrop of climate change, human population increase and subsequent rise in food demand, finding new solutions for crop adaptation to environmental stresses is essential. The effects of single abiotic stress on crops have been widely studied, but in the field abiotic stresses tend to occur in combination rather than individually. Physiological, metabolic and molecular responses of crops to combined abiotic stresses seem to be significantly different to individual stresses. Although in recent years an increasing number of studies have addressed the effects of abiotic stress combinations, the information related to the root system response is still scarce. Roots are the underground organs that directly contact with the soil and sense many of these abiotic stresses. Understanding the effects of abiotic stress combinations in the root system would help to find new breeding tools to develop more resilient crops. This review will summarize the current knowledge regarding the effects of combined abiotic stress in the root system in crops. First, we will provide a general overview of root responses to particular abiotic stresses. Then, we will describe how these root responses are integrated when crops are challenged to the combination of different abiotic stress. We will focus on the main changes on root system architecture (RSA) and physiology influencing crop productivity and yield and convey the latest information on the key molecular, hormonal and genetic regulatory pathways underlying root responses to these combinatorial stresses. Finally, we will discuss possible directions for future research and the main challenges needed to be tackled to translate this knowledge into useful tools to enhance crop tolerance.

Genome-wide analysis and transcriptional reprogrammings of MYB superfamily revealed positive insights into abiotic stress responses and anthocyanin accumulation in Carthamus tinctorius L

The MYB transcription factors comprise one of the largest superfamilies in plants that have been implicated in the regulation of plant-specific metabolites and responses to biotic and abiotic stresses. Here, we present the first comprehensive genome-wide analysis and functional characterization of the CtMYB family in Carthamus tinctorius. A total of 272 CtMYBs were identified and classified into 12 subgroups using comparative phylogenetic analysis with Arabidopsis and rice orthologs. The overview of conserved motifs, gene structures, and cis elements as well as the expression pattern of CtMYB genes indicated the diverse roles of these transcription factors during plant growth, regulation of secondary metabolites, and various abiotic stress responses. The subcellular localization and transactivation analysis of four CtMYB proteins indicated predominant localization in the nuclei with enhanced transcriptional activation in yeast. The expression of CtMYB63 induced with various abiotic stress conditions showed upregulation in its transcription level. In addition, the expression analysis of the core structural genes of anthocyanin biosynthetic pathway under drought and cold stress in CtMYB63 overexpressed transgenic lines also supports the notion of CtMYB63 transcriptional reprogramming in response to abiotic stress by upregulating the anthocyanin biosynthesis. Together, our findings revealed the underlying regulatory mechanism of CtMYB TF network involving enhanced cold and drought stress tolerance through activating the rapid biosynthesis of anthocyanin in C. tinctorius. This study also presents useful insights towards the establishment of new strategies for crop improvements.

The BTB/POZ domain protein GmBTB/POZ promotes the ubiquitination and degradation of the soybean AP2/ERF-like transcription factor GmAP2 to regulate the defense response to Phytophthora sojae

Phytophthora root and stem rot in soybean (Glycine max) is a destructive disease worldwide, and hence improving crop resistance to the causal pathogen, P. sojae, is a major target for breeders. However, it remains largely unclear how the pathogen regulates the various affected signaling pathways in the host, which consist of complex networks including key transcription factors and their targets. We have previously demonstrated that GmBTB/POZ enhances soybean resistance to P. sojae and the associated defense response. Here, we demonstrate that GmBTB/POZ interacts with the transcription factor GmAP2 and promotes its ubiquitination. GmAP2-RNAi transgenic soybean hairy roots exhibited enhanced resistance to P. sojae, whereas roots overexpressing GmAP2 showed hypersensitivity. GmWRKY33 was identified as a target of GmAP2, which represses its expression by directly binding to the promoter. GmWRKY33 acts as a positive regulator in the response of soybean to P. sojae. Overexpression of GmBTB/POZ released the GmAP2-regulated suppression of GmWRKY33 in hairy roots overexpressing GmAP2 and increased their resistance to P. sojae. Taken together, our results indicate that GmBTB/POZ-GmAP2 modulation of the P. sojae resistance response forms a novel regulatory mechanism, which putatively regulates the downstream target gene GmWRKY33 in soybean.

Genome-Wide Characterization of Salt-Responsive miRNAs, circRNAs and Associated ceRNA Networks in Tomatoes

Soil salinization is a major environmental stress that causes crop yield reductions worldwide. Therefore, the cultivation of salt-tolerant crops is an effective way to sustain crop yield. Tomatoes are one of the vegetable crops that are moderately sensitive to salt stress. Global market demand for tomatoes is huge and growing. In recent years, the mechanisms of salt tolerance in tomatoes have been extensively investigated; however, the molecular mechanism through which non-coding RNAs (ncRNAs) respond to salt stress is not well understood. In this study, we utilized small RNA sequencing and whole transcriptome sequencing technology to identify salt-responsive microRNAs (miRNAs), messenger RNAs (mRNAs), and circular RNAs (circRNAs) in roots of M82 cultivated tomato and Solanum pennellii (S. pennellii) wild tomato under salt stress. Based on the theory of competitive endogenous RNA (ceRNA), we also established several salt-responsive ceRNA networks. The results showed that circRNAs could act as miRNA sponges in the regulation of target mRNAs of miRNAs, thus participating in the response to salt stress. This study provides insights into the mechanisms of salt tolerance in tomatoes and serves as an effective reference for improving the salt tolerance of salt-sensitive cultivars.

Five OsS40 Family Members Are Identified as Senescence-Related Genes in Rice by Reverse Genetics Approach

A total of 16 OsS40 genes of Oryza sativa were identified in our previous work, but their functions remain unclear. In this study, 13 OsS40 members were knocked out using the CRISPR/cas9 gene-editing technology. After screening phenotype characterization of CRISPR/Cas9 mutants compared to WT, five oss40s mutants exhibited a stay-green phenotype at 30 days after heading. Moreover, increased grain size and grain weight occurred in the oss40-1, oss40-12, and oss40-14 lines, while declined grain weight appeared in the oss40-7 and oss40-13 mutants. The transcript levels of several senescence-associated genes (SAGs), chlorophyll degradation-related genes (CDGs), as well as WRKY members were differentially decreased in the five stay-green oss40s mutants compared to WT. Five oss40 mutants also exhibited a stay-green phenotype when the detached leaves were incubated under darkness for 4 days. OsSWEET4 and OsSWEET1b were significantly upregulated, while OsSWEET1a and OsSWEET13 were significantly downregulated in both oss40-7 and oss40-14 compared to WT. Furthermore, these five OsS40 displayed strong transcriptional activation activity and were located in the nucleus. Most of the OsS40 genes were downregulated in the oss40-1, oss40-7, and oss40-12 mutants, but upregulated in the oss40-13 and oss40-14 mutants, indicating coordinated regulation among OsS40 members. These results suggest that OsS40-1, OsS40-7, OsS40-12, OsS40-13, and OsS40-14 are senescence-associated genes, involved in the senescence and carbon allocation network by modulating other OsS40 members, SWEET member genes, and senescence-related gene expression.

Ectopic expression of poplar gene PsnERF138 in tobacco confers salt stress tolerance and growth advantages

The AP2/ERF family is one of the largest plant-specific transcription factors and plays a vital role in plant growth and stress response. In this study, PsnERF138 was cloned from Populus alba×Populus glandulosa and transformed into tobacco using the Agrobacterium-mediated transformation method. PsnERF138 was localized in the nucleus through subcellular localization assay in tobacco. Under normal conditions, the root lengths of PsnERF138 transgenic lines were much longer than those of wild type. Under salt stress, the transgenic tobacco lines over-expressing PsnERF138 showed a significant increase in seed germination rate, plant height, and root length, compared to control plants. In addition, the transgenic tobacco lines displayed some advantages at the physiological level, such as higher superoxide dismutase (SOD) activity, peroxidase (POD) activity, proline content, and lower malondialdehyde (MDA) content, as compared to those in the control plants. Histochemical staining also showed that the transgenic tobacco lines had lower reactive oxygen species (ROS) accumulation, compared to control plants under salt stress. The combined results indicate that poplar PsnERF138 plays a contributing role in augmenting salt tolerance and conferring multiple growth advantages as being overexpressed in tobacco.

Genome-Wide Association Mapping and Gene Expression Analysis Reveal the Negative Role of OsMYB21 in Regulating Bacterial Blight Resistance in Rice

BACKGROUND

Bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the most devastating diseases in rice all over the world. Due to the diversity and rapid evolution of Xoo, identification and use of the non-race specific quantitative resistance QTLs has been considered the preferred strategy for effective control of this disease. Although numerous QTLs for BB resistance have been identified, they haven't been effectively used for improvement of BB resistance in rice due to their small effects and lack of knowledge on the function of genes underlying the QTLs.

RESULTS

In the present study, a genome-wide association study of BB resistance was performed in a rice core collection from South China. A total of 17 QTLs were identified to be associated with BB resistance. Among them, 13 QTLs were newly identified in the present study and the other 4 QTLs were co-localized with the previously reported QTLs or Xa genes that confer qualitative resistance to Xoo strains. Particularly, the qBBR11-4 on chromosome 11 explained the largest phenotypic variation in this study and was co-localized with the previously identified QTLs for BB and bacterial leaf streak (BLS) resistance against diverse strains in three studies, suggesting its broad-spectrum resistance and potential value in rice breeding. Through combined analysis of differential expression and annotations of the predicted genes within qBBR11-4 between two sets of rice accessions selected based on haplotypes and disease phenotypes, we identified the transcription factor OsMYB21 as the candidate gene for qBBR11-4. The OsMYB21 overexpressing plants exhibited decreased resistance to bacterial blight, accompanied with down-regulation of several defense-related genes compared with the wild-type plants.

CONCLUSION

The results suggest that OsMYB21 negatively regulates bacterial blight resistance in rice, and this gene can be a promising target in rice breeding by using the gene editing method. In addition, the potential candidate genes for the 13 novel QTLs for BB resistance were also analyzed in this study, providing a new source for cloning of genes associated with BB resistance and molecular breeding in rice.

Identification of monocot chimeric jacalin family reveals functional diversity in wheat

MAIN CONCLUSION

46 monocot chimeric jacalins (MCJs) were mined from wheat genome. They were divided into three subfamilies with the activity of mannose-specific lectins and had effects on dehydration tolerance or disease resistance. Monocot chimeric jacalin (MCJ) is a newly identified subfamily of plant lectins that exclusively exists in Poaceae. The MCJs are modular proteins consisting of a dirigent domain and a jacalin-related lectin domain. Their unique evolution and various functions are not fully understood as only few members of MCJ have so for been investigated. From wheat, 46 MCJs were identified and phylogenetically classified into three subfamilies, in which subfamily I represented the early evolutionary cluster. MCJ genes are evenly distributed among three subgenomes of wheat, indicating that MCJ might be an ancient gene in Poaceae. qRT-PCR analysis showed that TaMCJ1 and TaMCJ2 were mainly expressed in leaves while TaMCJ3 in root tissues. All these TaMCJ genes are JA or ABA inducible. All three proteins exhibited agglutinating activity but different preference to mannose-binding. The overexpression of TaMCJ3 in tobacco increased dehydration tolerance, while TaMCJ1 enhanced wildfire disease resistance. The lignin biosynthetic genes were temporarily induced after pathogen inoculation in transgenic tobacco overexpressing TaMCJ, but the specific association with TaMCJ was not established. This evidence argued against the notion that the dirigent domain in TaMCJ is directly linked with lignin metabolism. Taken together, these results pave the way for a better understanding of the manifold functionality of MCJs and offer important insights to the evolutionary history of MCJ.

Maize Ethylene Response Factor ZmERF061 Is Required for Resistance to Exserohilum turcicum

Plants have evolved a series of sophisticated defense mechanisms to help them from harm. Ethylene Response Factor (ERF) plays pivotal roles in plant immune reactions, however, its underlying mechanism in maize with a defensive function to Exserohilum turcicum (E. turcicum) remains poorly understood. Here, we isolated and characterized a novel ERF transcription factor, designated ZmERF061, from maize. Phylogenetic analysis revealed that ZmERF061 is a member of B3 group in the ERF family. qRT-PCR assays showed that the expression of ZmERF061 is significantly induced by E. turcicum inoculation and hormone treatments with salicylic acid (SA) and methyl jasmonate (MeJA). ZmERF061 was proved to function as a nucleus-localized transcription activator and specifically bind to the GCC-box element. zmerf061 mutant lines resulted in enhanced susceptibility to E. turcicum via decreasing the expression of ZmPR10.1 and ZmPR10.2 and the activity of antioxidant defense system. zmerf061 mutant lines increased the expression of the SA signaling-related gene ZmPR1a and decreased the expression of the jasmonic acid (JA) signaling-related gene ZmLox1 after infection with E. turcicum. In addition, ZmERF061 could interact with ZmMPK6-1. These results suggested that ZmERF061 plays an important role in response to E. turcicum and may be useful in genetic engineering breeding.

Identification of conserved genes linked to responses to abiotic stresses in leaves among different plant species

As a consequence of global climate change, certain stress factors that have a negative impact on crop productivity such as heat, cold, drought and salinity are becoming increasingly prevalent. We conducted a meta-analysis to identify genes conserved across plant species involved in (1) general abiotic stress conditions, and (2) specific and unique abiotic stress factors (drought, salinity, extreme temperature) in leaf tissues. We collected raw data and re-analysed eight RNA-Seq studies using our previously published bioinformatic pipeline. A total of 68 samples were analysed. Gene set enrichment analysis was performed using MapMan and PageMan whereas DAVID (Database for Annotation, Visualisation and Integrated Discovery) was used for metabolic process enrichment analysis. We identified of a total of 5122 differentially expressed genes when considering all abiotic stresses (3895 were upregulated and 1227 were downregulated). Jasmonate-related genes were more commonly upregulated by drought, whereas gibberellin downregulation was a key signal for drought and heat. In contrast, cold stress clearly upregulated genes involved in ABA (abscisic acid), cytokinin and gibberellins. A gene (non-phototrophic hypocotyl) involved in IAA (indoleacetic acid) response was induced by heat. Regarding secondary metabolism, as expected, MVA pathway (mevalonate pathway), terpenoids and alkaloids were generally upregulated by all different stresses. However, flavonoids, lignin and lignans were more repressed by heat (cinnamoyl coA reductase 1 and isopentenyl pyrophosphatase). Cold stress drastically modulated genes involved in terpenoid and alkaloids. Relating to transcription factors, AP2-EREBP, MADS-box, WRKY22, MYB, homoebox genes members were significantly modulated by drought stress whereas cold stress enhanced AP2-EREBPs, bZIP members, MYB7, BELL 1 and one bHLH member. C2C2-CO-LIKE, MADS-box and a homeobox (HOMEOBOX3) were mostly repressed in response to heat. Gene set enrichment analysis showed that ubiquitin-mediated protein degradation was enhanced by heat, which unexpectedly repressed glutaredoxin genes. Cold stress mostly upregulated MAP kinases (mitogen-activated protein kinase). Findings of this work will allow the identification of new molecular markers conserved across crops linked to major genes involved in quantitative agronomic traits affected by different abiotic stress.

Identification and Analysis of NBS-LRR Genes in Actinidia chinensis Genome

Nucleotide-binding site and leucine-rich repeat (NBS-LRR) genes represent the most important disease resistance genes in plants. The genome sequence of kiwifruit (Actinidia chinensis) provides resources for the characterization of NBS-LRR genes and identification of new R-genes in kiwifruit. In the present study, we identified 100 NBS-LRR genes in the kiwifruit genome and they were grouped into six distinct classes based on their domain architecture. Of the 100 genes, 79 are truncated non-regular NBS-LRR genes. Except for 37 NBS-LRR genes with no location information, the remaining 63 genes are distributed unevenly across 18 kiwifruit chromosomes and 38.01% of them are present in clusters. Seventeen families of cis-acting elements were identified in the promoters of the NBS-LRR genes, including AP2, NAC, ERF and MYB. Pseudomonas syringae pv. actinidiae (pathogen of the kiwifruit bacterial canker) infection induced differential expressions of 16 detected NBS-LRR genes and three of them are involved in plant immunity responses. Our study provides insight of the NBS-LRR genes in kiwifruit and a resource for the identification of new R-genes in the fruit.

Identification of a novel ERF gene, TaERF8, associated with plant height and yield in wheat

BACKGROUND

Ethylene Responsive Factor (ERF) is involved in various processes of plant development and stress responses. In wheat, several ERFs have been identified and their roles in mediating biotic or abiotic stresses have been elucidated. However, their effects on wheat plant architecture and yield-related traits remain poorly studied.

RESULTS

In this study, TaERF8, a new member of the ERF family, was isolated in wheat (Triticum aestivum L.). Three homoeologous TaERF8 genes, TaERF8-2A, TaERF8-2B and TaERF8-2D (named according to sub-genomic origin), were cloned from the common wheat cultivar Chinese Spring. The three homoeologs showed highly similar protein sequences, with identical AP2 domain. Whereas homoeologs sequence polymorphism analysis allowed the establishment of ten, two and three haplotypes, respectively. Expression analysis revealed that TaERF8s were constitutively expressed through entire wheat developmental stages. Analysis of related agronomic traits of TaERF8-2B overexpressing transgenic lines showed that TaERF8-2B plays a role in regulating plant architecture and yield-related traits. Association analysis between TaERF8-2B haplotypes (Hap-2B-1 and Hap-2B-2) and agronomic traits showed that TaERF8-2B was associated with plant height, heading date and 1000 kernel weight (TKW). The TaERF8-2B haplotypes distribution analysis revealed that Hap-2B-2 frequency increased in domesticated emmer wheat and modern varieties, being predominant in five major China wheat producing zones.

CONCLUSION

These results indicated that TaERF8s are differentially involved in the regulation of wheat growth and development. Haplotype Hap-2B-2 was favored during domestication and in Chinese wheat breeding. Unveiling that the here described molecular marker TaERF8-2B-InDel could be used for marker-assisted selection, plant architecture and TKW improvement in wheat breeding.

Apple ethylene response factor MdERF11 confers resistance to fungal pathogen Botryosphaeria dothidea

Ethylene response factor (ERF) is a plant-specific transcription factor involved in many biological processes including root formation, hypocotyl elongation, fruit ripening, organ senescence and stress responses, as well as fruit quality formation. However, its underlying mechanism in plant pathogen defense against Botryosphaeria dothidea (B. dothidea) remains poorly understood. Here, we isolate MdERF11, an apple nucleus-localized ERF transcription factor, from apple cultivar 'Royal Gala'. qRT-PCR assays show that the expression of MdERF11 is significantly induced in apple fruits after B. dothidea infection. Overexpression of MdERF11 gene in apple calli significantly increases the resistance to B.dothidea infection, while silencing MdERF11 in apple calli results in reduced resistance. Ectopic expression of MdERF11 in Arabidopsis also exhibits enhanced resistance to B. dothidea infection compared to that of wild type. Infections in apple calli and Arabidopsis leaves by B. dothidea respectively cause an increase in endogenous levels of salicylic acid (SA) followed by induction of SA synthesis-related and signaling-related gene expression. Taken together, these findings illustrate a potential mechanism by which MdERF11 elevates plant pathogen defense against B. dothidea by regulating SA synthesis pathway.

Isolation, sequencing, and expression analysis of 30 AP2/ERF transcription factors in apple

BACKGROUND

AP2/ERF transcription factors are involved in the regulation of plant growth, development, and stress responses. Our research objective was to characterize novel apple (Malus × domestica Borkh.) genes encoding AP2/ERF transcription factors involved in regulation of plant growth, development, and stress response. The transcriptional level of apple AP2/ERF genes in different tissues and under various biotic and abiotic stress was determined to provide valuable insights into the function of AP2/ERF transcription factors in apple.

METHODS

Thirty full-length cDNA sequences of apple AP2/ERF genes were isolated from 'Zihong Fuji' apple (Malus × domestica cv. Zihong Fuji) via homologous comparison and RT-PCR confirmation, and the obtained cDNA sequences and the deduced amino acid sequences were analyzed with bioinformatics methods. Expression levels of apple AP2/ERF genes were detected in 16 different tissues using a known array. Expression patterns of apple AP2/ERF genes were detected in response to Alternaria alternata apple pathotype (AAAP) infection using RNA-seq with existing data, and the expression of apple AP2/ERF genes was analyzed under NaCl and mannitol treatments using qRT-PCR.

RESULTS

The sequencing results produced 30 cDNAs (designated as MdERF3-8, MdERF11, MdERF16-19, MdERF22-28, MdERF31-35, MdERF39, MdAP2D60, MdAP2D62-65, and MdRAV2). Phylogenetic analysis revealed that MdERF11/16, MdERF33/35, MdERF34/39, and MdERF18/23 belonged to groups A-2, A-4, A-5, and A-6 of the DREB subfamily, respectively; MdERF31, MdERF19, MdERF4/25/28/32, MdERF24, MdERF5/6/27, and MdERF3/7/8/17/22/26 belonged to groups B-1, B-2, B-3, B-4, B-5, and B-6 of the ERF subfamily, respectively; MdAP2D60 and MdAP2D62/63/64/65 belonged to the AP2 subfamily; and MdRAV2 belonged to the RAV subfamily. Array results indicated that 30 apple AP2/ERF genes were expressed in all examined tissues to different degrees. RNA-seq results using previously reported data showed that many members of the apple ERF and DREB subfamilies were induced by Alternaria alternate apple pathotype (AAAP) infection. Under salt treatment, many members in the apple ERF and DREB subfamilies were transcriptionally up or down-regulated. Under mannitol treatment, many members of the apple ERF, DREB, and AP2 subfamilies were induced at the transcriptional level. Taken together, the results indicated that the cloned apple AP2/ERF genes were expressed in all examined tissues. These genes were up-regulated or down-regulated in response to AAAP infection and to salt or mannitol treatment, which suggested they may be involved in regulating growth, development, and stress response in apple.

Identification of MicroRNAs That Respond to Soybean Cyst Nematode Infection in Early Stages in Resistant and Susceptible Soybean Cultivars

Soybean cyst nematode (SCN) causes heavy losses to soybean yield. In order to investigate the roles of soybean miRNAs during the early stages of infection (1 and 5 dpi), 24 small RNA libraries were constructed from SCN resistant cultivar Huipizhi (HPZ) and the susceptible Williams 82 (W82) cultivar for high-throughput sequencing. By sequencing the small RNA libraries, a total of 634 known miRNAs were identified, and 252 novel miRNAs were predicted. Altogether, 14 known miRNAs belonging to 13 families, and 26 novel miRNAs were differentially expressed and may respond to SCN infection in HPZ and W82. Similar expression results were also confirmed by qRT-PCR. Further analysis of the biological processes that these potential target genes of differentially expressed miRNAs regulate found that they may be strongly related to plant-pathogen interactions. Overall, soybean miRNAs experience profound changes in early stages of SCN infection in both HPZ and W82. The findings of this study can provide insight into miRNAome changes in both HPZ and W82 at the early stages of infection, and may provide a stepping stone for future SCN management.

The rice ethylene response factor OsERF83 positively regulates disease resistance to Magnaporthe oryzae

Rice blast caused by Magnaporthe oryzae is one of the most destructive diseases of rice (Oryza sativa) worldwide. Here, we report the identification and functional characterization of a novel ethylene response factor (ERF) gene, OsERF83, which was expressed in rice leaves in response to rice blast fungus infection. OsERF83 expression was also induced by treatments with methyl jasmonate, ethephon, and salicylic acid, indicating that multiple phytohormones could be involved in the regulation of OsERF83 expression under biotic stress. Subcellular localization and transactivation analyses demonstrated that OsERF83 is a nucleus-localized transcriptional activator. A gel-shift assay using recombinant OsERF83 protein indicated that, like other ERFs, it binds to the GCC box. Transgenic rice plants overexpressing OsERF83 exhibited significantly suppressed lesion formation after rice blast infection, indicating that OsERF83 positively regulates disease resistance in rice. Genes encoding several classes of pathogenesis-related (PR) proteins, including PR1, PR2, PR3, PR5, and PR10, were upregulated in the OsERF83ox plants. Taken together, our findings show that OsERF83 is a novel ERF transcription factor that confers blast resistance by regulating the expression of defense-related genes in rice.

Consensus map integration and QTL meta-analysis narrowed a locus for yield traits to 0.7 cM and refined a region for late leaf spot resistance traits to 0.38 cM on linkage group A05 in peanut (Arachis hypogaea L.)

BACKGROUND

Many large-effect quantitative trait loci (QTLs) for yield and disease resistance related traits have been identified in different mapping populations of peanut (Arachis hypogaea L.) under multiple environments. However, only a limited number of QTLs have been used in marker-assisted selection (MAS) because of unfavorable epistatic interactions between QTLs in different genetic backgrounds. Thus, it is essential to identify consensus QTLs across different environments and genetic backgrounds for use in MAS. Here, we used QTL meta-analysis to identify a set of consensus QTLs for yield and disease resistance related traits in peanut.

RESULTS

A new integrated consensus genetic map with 5874 loci was constructed. The map comprised 20 linkage groups (LGs) and was up to a total length of 2918.62 cM with average marker density of 2.01 loci per centimorgan (cM). A total of 292 initial QTLs were projected on the new consensus map, and 40 meta-QTLs (MQTLs) for yield and disease resistance related traits were detected on four LGs. The genetic intervals of these consensus MQTLs varied from 0.20 cM to 7.4 cM, which is narrower than the genetic intervals of the initial QTLs, meaning they may be suitable for use in MAS. Importantly, a region of the map that previously co-localized multiple major QTLs for pod traits was narrowed from 3.7 cM to 0.7 cM using an overlap region of four MQTLs for yield related traits on LG A05, which corresponds to a physical region of about 630.3 kb on the A05 pseudomolecule of peanut, including 38 annotated candidate genes (54 transcripts) related to catalytic activity and metabolic process. Additionally, one major MQTL for late leaf spot (LLS) was identified in a region of about 0.38 cM. BLAST searches identified 26 candidate genes (30 different transcripts) in this region, some of which were annotated as related to regulation of disease resistance in different plant species.

CONCLUSIONS

Combined with the high-density marker consensus map, all the detected MQTLs could be useful in MAS. The biological functions of the 64 candidate genes should be validated to unravel the molecular mechanisms of yield and disease resistance in peanut.

OsTGA2 confers disease resistance to rice against leaf blight by regulating expression levels of disease related genes via interaction with NH1

How plants defend themselves from microbial infection is one of the most critical issues for sustainable crop production. Some TGA transcription factors belonging to bZIP superfamily can regulate disease resistance through NPR1-mediated immunity mechanisms in Arabidopsis. Here, we examined biological roles of OsTGA2 (grouped into the same subclade as Arabidopsis TGAs) in bacterial leaf blight resistance. Transcriptional level of OsTGA2 was accumulated after treatment with salicylic acid, methyl jasmonate, and Xathomonas oryzae pv. Oryzae (Xoo), a bacterium causing serious blight of rice. OsTGA2 formed homo- and hetero-dimer with OsTGA3 and OsTGA5 and interacted with rice NPR1 homologs 1 (NH1) in rice. Results of quadruple 9-mer protein-binding microarray analysis indicated that OsTGA2 could bind to TGACGT DNA sequence. Overexpression of OsTGA2 increased resistance of rice to bacterial leaf blight, although overexpression of OsTGA3 resulted in disease symptoms similar to wild type plant upon Xoo infection. Overexpression of OsTGA2 enhanced the expression of defense related genes containing TGA binding cis-element in the promoter such as AP2/EREBP 129, ERD1, and HOP1. These results suggest that OsTGA2 can directly regulate the expression of defense related genes and increase the resistance of rice against bacterial leaf blight disease.

Plant Hormone Signaling Crosstalks between Biotic and Abiotic Stress Responses

In the natural environment, plants are often bombarded by a combination of abiotic (such as drought, salt, heat or cold) and biotic (necrotrophic and biotrophic pathogens) stresses simultaneously. It is critical to understand how the various response pathways to these stresses interact with one another within the plants, and where the points of crosstalk occur which switch the responses from one pathway to another. Calcium sensors are often regarded as the first line of response to external stimuli to trigger downstream signaling. Abscisic acid (ABA) is a major phytohormone regulating stress responses, and it interacts with the jasmonic acid (JA) and salicylic acid (SA) signaling pathways to channel resources into mitigating the effects of abiotic stresses versus defending against pathogens. The signal transduction in these pathways are often carried out via GTP-binding proteins (G-proteins) which comprise of a large group of proteins that are varied in structures and functions. Deciphering the combined actions of these different signaling pathways in plants would greatly enhance the ability of breeders to develop food crops that can thrive in deteriorating environmental conditions under climate change, and that can maintain or even increase crop yield.

Soil sustainable utilization technology: mechanism of flavonols in resistance process of heavy metal

The soil ecosystem is critical for agricultural production, affecting many aspects of human health. Soil has more unknown biodiversity and edaphic parameters than any other ecosystem especially when polluted. Metagenomics and metatranscriptomics were applied to research on toxicological characteristics of Pb and resistance mechanism of flavonols. Rhizosphere microorganisms-plants system, a unified system closely related to soil environment was taken as research object. Results emphasize gene expression changes in different test groups. Gene ontology enrichment and eggNOG showed that Pb has a toxic effect on gene and protein function which concentrated on ATPase and ATP-dependent activity. Differentially expressed genes in the flavonols group indicated that flavonols regulate amino acid transport and other transportation process related to Pb stress. Kegg analysis represents that Pb interferences energy production process via not only the upstream like glycolysis and tricarboxylic acid (TCA) circle but also oxidative phosphorylation process, which can also produce reactive oxygen species and impact the eliminating process. Flavonols have shown the ability in alleviating toxic effect of Pb and improving the resistance of plants. Flavonols can recover the electronic transmission and other process in TCA and oxidative phosphorylation via ascorbic acid-glutathione metabolism. Flavonols activated antioxidative process and non-specific immunity via vitamins B₂-B₆ metabolism.

CRISPR Crops: Plant Genome Editing Toward Disease Resistance

Genome editing by sequence-specific nucleases (SSNs) has revolutionized biology by enabling targeted modifications of genomes. Although routine plant genome editing emerged only a few years ago, we are already witnessing the first applications to improve disease resistance. In particular, CRISPR-Cas9 has democratized the use of genome editing in plants thanks to the ease and robustness of this method. Here, we review the recent developments in plant genome editing and its application to enhancing disease resistance against plant pathogens. In the future, bioedited disease resistant crops will become a standard tool in plant breeding.

Can-miRn37a mediated suppression of ethylene response factors enhances the resistance of chilli against anthracnose pathogen Colletotrichum truncatum L

Pepper anthracnose, caused by Colletotrichum species complex is the most destructive disease of chilli (Capsicum annuum L.). miRNAs are key modulators of transcriptional and post- transcriptional expression of genes during defense responses. In the present study, we performed a comparative miRNA profiling of susceptible (Arka Lohit-AL) and resistant (Punjab Lal-PL) chilli cultivars to identify 35 differentially expressed miRNAs that could be classified as positive, negative or basal regulators of defense against C. truncatum, the most potent anthracnose pathogen. Interestingly, a novel microRNA can-miRn37a was significantly induced in PL but largely repressed in AL genotype post pathogen attack. Subsequent over-expression of can-miRn37a in AL showed enhanced resistance to anthracnose, as evidenced by decreased fungal growth and induced expression of defense-related genes. Consequently, the expression of its three target genes encoding the ethylene response factors (ERFs) was down-regulated in PL as well as in the over-expression lines of AL genotypes. The ability of these targets to be regulated by can-miRn37a was further confirmed by transient co-expression in Nicotiana benthamiana. Additionally, the virus-induced silencing of the three targets in the susceptible AL cultivar revealed their role in fungal colonization and induction of C. truncatum pathogenicity in chilli. Taken together, our study suggests that can-miRn37a provides a potential miRNA mediated approach of engineering anthracnose resistance in chilli by repressing ERFs and preventing fungal colonization.

Identification and functional prediction of stress responsive AP2/ERF transcription factors in Brassica napus by genome-wide analysis

Using homology and domain authentication, 321 putative AP2/ERF transcription factors were identified in Brassica napus, called BnAP2/ERF TFs. BnAP2/ERF TFs were classified into five major subfamilies, including DREB, ERF, AP2, RAV, and BnSoloist. This classification is based on phylogenetic analysis, motif identification, gene structure analysis, and physiochemical characterization. These TFs were annotated based on phylogenetic relationship with Brassica rapa. BnAP2/ERF TFs were located on 19 chromosomes of B. napus. Orthologs and paralogs were identified using synteny-based methods Ks calculation within B. napus genome and between B. napus with other species such as B. rapa, Brassica oleracea, and Arabidopsis thaliana indicated that BnAP2/ERF TFs were formed through duplication events occurred before B. napus formation. Kn/Ks values were between 0 and 1, suggesting the purifying selection among BnAP2/ERF TFs. Gene ontology annotation, cis-regulatory elements and functional interaction networks suggested that BnAP2/ERF TFs participate in response to stressors, including drought, high salinity, heat and cold as well as developmental processes particularly organ specification and embryogenesis. The identified cis-regulatory elements in the upstream of BnAP2/ERF TFs were responsive to abscisic acid. Analysis of the expression data derived from Illumina Hiseq 2000 RNA sequencing revealed that BnAP2/ERF genes were highly expressed in the roots comparing to flower buds, leaves, and stems. Also, the ERF subfamily was over-expressed under salt and fungal treatments. BnERF039 and BnERF245 are candidates for salt-tolerant B. napus. BnERF253-256 and BnERF260-277 are potential cytokinin response factors. BnERF227, BnERF228, BnERF234, BnERF134, BnERF132, BnERF176, and BnERF235 were suggested for resistance against Leptosphaeria maculan and Leptosphaeria biglobosa.

Wheat ROP proteins modulate defense response through lignin metabolism

ROP is a subfamily of small GTP-binding proteins that uniquely exist in plants. It acts as versatile molecular switches that regulate various developmental processes. Some ROP proteins are also reported to affect defense responses, although their exact mechanism is not fully understood. Herein, ROP members in wheat were mined; the functions of three wheat ROP proteins were studied. RT-PCR results showed that the expression of TaRac1 was rapidly and strongly induced after leaf rust infection. TaRac1 interacted with TaCCR in yeast-hybridization assay. The overexpression of TaRac1 in tobacco promoted CCR and CAD gene expression, increased the total lignin content and sinapyl lignin proportion, and then enhanced resistance to tobacco black shank and bacterial wilt diseases. In contrast, TaRac3 and TaRac4 did not show to interact with TaCCR. Furthermore, the overexpression of TaRac3 and TaRac4 did not increase lignin gene expression and lignin accumulation either. Unlike TaRac1, the overexpression of TaRac3 increased susceptibility to both black shank and bacterial wilt pathogens, while overexpression of TaRac4 showed no effect on disease resistance but promoted the root growth in tobacco seedling. These data collectively suggest that TaRac1 in Group II is mainly involved in regulating lignin metabolism which, in turn, responsible for the observed roles in pathogen resistance. TaRac3 and TaRac4 have the minor roles in defense response but may act on regulation in plant developmental processes. These results shed light on the complexity and diverse function of ROP in plant defense pathway.

Transgenic poplar overexpressing the endogenous transcription factor ERF76 gene improves salinity tolerance

The ethylene response factor (ERF) family is one of the largest plant-specific transcription factor families, playing an important role in plant development and response to stresses. The ERF76 gene is a member of the poplar ERF transcription factor gene family. First, we validated that the ERF76 gene expressed in leaf and root tissues is responsive to salinity stress. We then successfully cloned the ERF76 cDNA fragment containing an open reading frame from di-haploid Populus simonii × Populus nigra and proved that ERF76 protein is targeted to the nucleus. Finally, we transferred the gene into the same poplar clone by the Agrobacterium-mediated leaf disc method. Using both RNA-Seq and reverse transcription-quantitative polymerase chain reaction, we validated that expression level of ERF76 is significantly higher in transgenic plants than that in the nontransgenic control. Using RNA-Seq data, we have identified 375 genes that are differentially expressed between the transgenic plants and the control under salt treatment. Among the differentially expressed genes, 16 are transcription factor genes and 45 are stress-related genes, both of which are upregulated significantly in transgenic plants, compared with the control. Under salt stress, the transgenic plants showed significant increases in plant height, root length, fresh weight, and abscisic acid (ABA) and gibberellin (GA) concentration compared with the control, suggesting that overexpression of ERF76 in transgenic poplar upregulated the expression of stress-related genes and increased the ability of ABA and GA biosynthesis, which resulted in stronger tolerance to salt stress.

Laminarin modulates the chloroplast antioxidant system to enhance abiotic stress tolerance partially through the regulation of the defensin-like gene expression

Algae wall polysaccharide, laminarin (Lam), has an established role on induction of plant disease resistance. In this study, application of Lam increased Arabidopsis fresh weight and enhanced tolerance to salt and heat stress by stabilizing chloroplast under adverse environment. Transcriptome analysis indicated that, in addition to induced a large number of genes associated with the host defense, genes involved in the regulation of abiotic stress tolerance mostly the heat stress response constituted the largest group of the up-regulated genes. Lam induced expression of IRT1, ZIP8, and copper transporters involved in transport of Fe, Zn, Cu ions associated with the activity of chloroplast antioxidant system. Lam also up-regulated genes involved in the synthesis of terpenoid, a plastidial-derived secondary metabolite with antioxidant activity. Overexpression of a Lam-induced defensin like 202 (DEFL202) resulted in increased chloroplast stability under salt stress and increased plant growth activity after heat stress. Expression of antioxidant enzymes including SOD and ascorbate peroxidase (APX), photosystem PsbA-D1 and ABA-dependent responsive to desiccation 22 (RD22) was induced to higher levels in the transgenic seedlings. In sum, our results suggest that Lam is an potent inducer for induction of chloroplastic antioxidant activity. Lam affect plant abiotic stress tolerance partially through regulation of the DEFL-mediated pathway.

Tomato SlERF.A1, SlERF.B4, SlERF.C3 and SlERF.A3, Members of B3 Group of ERF Family, Are Required for Resistance to Botrytis cinerea

The Ethylene-Responsive Factors (ERFs) comprise a large family of transcriptional factors that play critical roles in plant immunity. Gray mold disease caused by Botrytis cinerea, a typical necrotrophic fungal pathogen, is the serious disease that threatens tomato production worldwide. However, littler is known about the molecular mechanism regulating the immunity to B. cinerea in tomato. In the present study, virus-induced gene silencing (VIGS)-based functional analyses of 18 members of B3 group (also called Group IX) in tomato ERF family were performed to identify putative ERFs that are involved in disease resistance against B. cinerea. VIGS-based silencing of either SlERF.B1 or SlERF.C2 had lethal effect while silencing of SlERF.A3 (Pit4) significantly suppressed vegetative growth of tomato plants. Importantly, silencing of SlERF.A1, SlERF.A3, SlERF.B4, or SlERF.C3 resulted in increased susceptibility to B. cinerea, attenuated the B. cinerea-induced expression of jasmonic acid/ethylene-mediated signaling responsive defense genes and promoted the B. cinerea-induced H₂O₂ accumulation. However, silencing of SlERF.A3 also decreased the resistance against Pseudomonas syringae pv. tomato (Pst) DC3000 but silencing of SlERF.A1, SlERF.B4 or SlERF.C3 did not affect the resistance to this bacterial pathogen. Expression of SlERF.A1, SlERF.A3, SlERF.B4, or SlERF.C3 was induced by B. cinerea and by defense signaling hormones such as salicylic acid, methyl jasmonate, and 1-aminocyclopropane-1-carboxylic acid (an ethylene precursor). SlERF.A1, SlERF.B4, SlERF.C3, and SlERF.A3 proteins were found to localize in nucleus of cells and possess transactivation activity in yeasts. These data suggest that SlERF.A1, SlERF.B4, and SlERF.C3, three previously uncharacterized ERFs in B3 group, and SlERF.A3, a previously identified ERF with function in immunity to Pst DC3000, play important roles in resistance against B. cinerea in tomato.

Crystal structure of an antifungal osmotin-like protein from Calotropis procera and its effects on Fusarium solani spores, as revealed by atomic force microscopy: Insights into the mechanism of action

CpOsm is an antifungal osmotin/thaumatin-like protein purified from the latex of Calotropis procera. The protein is relatively thermostable and retains its antifungal activity over a wide pH range; therefore, it may be useful in the development of new antifungal drugs or transgenic crops with enhanced resistance to phytopathogenic fungi. To gain further insight into the mechanism of action of CpOsm, its three-dimensional structure was determined, and the effects of the protein on Fusarium solani spores were investigated by atomic force microscopy (AFM). The atomic structure of CpOsm was solved at a resolution of 1.61Å, and it contained 205 amino acid residues and 192 water molecules, with a final R-factor of 18.12% and an Rfree of 21.59%. The CpOsm structure belongs to the thaumatin superfamily fold and is characterized by three domains stabilized by eight disulfide bonds and a prominent charged cleft, which runs the length of the front side of the molecule. Similarly to other antifungal thaumatin-like proteins, the cleft of CpOsm is predominantly acidic. AFM images of F. solani spores treated with CpOsm resulted in striking morphological changes being induced by the protein. Spores treated with CpOsm were wrinkled, and the volume of these cells was reduced by approximately 80%. Treated cells were covered by a shell of CpOsm molecules, and the leakage of cytoplasmic content from these cells was also observed. Based on the structural features of CpOsm and the effects that the protein produces on F. solani spores, a possible mechanism of action is suggested and discussed.

Identification and Molecular Characterization of the Switchgrass AP2/ERF Transcription Factor Superfamily, and Overexpression of PvERF001 for Improvement of Biomass Characteristics for Biofuel

The APETALA2/ethylene response factor (AP2/ERF) superfamily of transcription factors (TFs) plays essential roles in the regulation of various growth and developmental programs including stress responses. Members of these TFs in other plant species have been implicated to play a role in the regulation of cell wall biosynthesis. Here, we identified a total of 207 AP2/ERF TF genes in the switchgrass genome and grouped into four gene families comprised of 25 AP2-, 121 ERF-, 55 DREB (dehydration responsive element binding)-, and 5 RAV (related to API3/VP) genes, as well as a singleton gene not fitting any of the above families. The ERF and DREB subfamilies comprised seven and four distinct groups, respectively. Analysis of exon/intron structures of switchgrass AP2/ERF genes showed high diversity in the distribution of introns in AP2 genes versus a single or no intron in most genes in the ERF and RAV families. The majority of the subfamilies or groups within it were characterized by the presence of one or more specific conserved protein motifs. In silico functional analysis revealed that many genes in these families might be associated with the regulation of responses to environmental stimuli via transcriptional regulation of the response genes. Moreover, these genes had diverse endogenous expression patterns in switchgrass during seed germination, vegetative growth, flower development, and seed formation. Interestingly, several members of the ERF and DREB families were found to be highly expressed in plant tissues where active lignification occurs. These results provide vital resources to select candidate genes to potentially impart tolerance to environmental stress as well as reduced recalcitrance. Overexpression of one of the ERF genes (PvERF001) in switchgrass was associated with increased biomass yield and sugar release efficiency in transgenic lines, exemplifying the potential of these TFs in the development of lignocellulosic feedstocks with improved biomass characteristics for biofuels.

The Potato ERF Transcription Factor StERF3 Negatively Regulates Resistance to Phytophthora infestans and Salt Tolerance in Potato

Ethylene response factors (ERFs) are unique to the plant kingdom and play crucial roles in plant response to various biotic and abiotic stresses. We show here that a potato StERF3, which contains an ERF-associated amphiphilic repression (EAR) motif in its C-terminal region, negatively regulates resistance to Phytophthora infestans and salt tolerance in potato. The StERF3 promoter responds to induction by salicylic acid, ABA ethylene and NaCl, as well as P. infestans, the causal agent of potato late blight disease. StERF3 could bind to the GCC box element of the HIS3 promoter and activate transcription of HIS3 in yeast cells. Importantly, silencing of StERF3 in potato produced an enhanced foliage resistance to P. infestans and elevated plant tolerance to NaCl stress accompanied by the activation of defense-related genes (PR1, NPR1 and WRKY1). In contrast, StERF3-overexpressing plants showed reduced expression of these defense-related genes and enhanced susceptibility to P. infestans, suggesting that StERF3 functions as a negative regulator of downstream defense- and/or stress-related genes in potato. StERF3 is localized to the nucleus. Interestingly, yeast two-hybrid assay and a bimolecular fluorescence complementation (BiFC) test clarified that StERF3 could interact with other proteins in the cytoplasm which may lead to its re-localization between the nucleus and cytoplasm, revealing a novel means of StERF3 regulation. Taken together, these data provide new insights into the mechanism underlying how StERF3 negatively regulates late blight resistance and abiotic tolerance in potato and may have a potential use in engineering late blight resistance in potato.

Trihelix transcription factor GT-4 mediates salt tolerance via interaction with TEM2 in Arabidopsis

BACKGROUND

Trihelix transcription factor family is plant-specific and plays important roles in developmental processes. However, their function in abiotic stress response is largely unclear.

RESULTS

We studied one member GT-4 from Arabidopsis in relation to salt stress response. GT-4 expression is induced by salt stress and GT-4 protein is localized in nucleus and cytoplasm. GT-4 acts as a transcriptional activator and its C-terminal end is the activation domain. The protein can bind to the cis-elements GT-3 box, GT-3b box and MRE4. GT-4 confers enhanced salt tolerance in Arabidopsis likely through direct binding to the promoter and activation of Cor15A, in addition to possible regulation of other relevant genes. The gt-4 mutant shows salt sensitivity. TEM2, a member of AP2/ERF family was identified to interact with GT-4 in yeast two-hybrid, BiFC and Co-IP assays. Loss-of-function of TEM2 exerts no significant difference on salt tolerance or Cor15A expression in Arabidopsis. However, double mutant gt-4/tem2 shows greater sensitivity to salt stress and lower transcript level of Cor15A than gt-4 single mutant. GT-4 plus TEM2 can synergistically increase the promoter activity of Cor15A.

CONCLUSIONS

GT-4 interacts with TEM2 and then co-regulates the salt responsive gene Cor15A to improve salt stress tolerance.

Na⁺/H⁺ exchanger 1 participates in tobacco disease defence against Phytophthora parasitica var. nicotianae by affecting vacuolar pH and priming the antioxidative system

Despite the importance of NHX1 (Na(+)/H(+) exchanger 1) in plant salt tolerance, little is known about its other functions. In this study, intriguingly, it was found that NHX1 participated in plant disease defence against Phytophthora parasitica var. nicotianae (Ppn) in Nicotiana benthamiana. NbNHX1 was originally isolated from N. benthamiana, and characterized. The subcellular localization of NbNHX1 with its C-terminus fused with green fluorescent protein indicated that NbNHX1 localized primarily to the tonoplast. Tobacco rattle virus-induced NbNHX1 silencing led to reduced H(+) efflux from the vacuole to cytoplasts, and decreased Ppn resistance in N. benthamiana. After attack by Ppn, NbNHX1-silenced plants exhibited impaired ability to scavenge reactive oxidative species (ROS) induced by the pathogen. Pea early browning virus-mediated ectopic expression of SeNHX1 (from Salicornia europaea) or AtNHX1 (from Arabidopsis thaliana) both conferred enhanced Ppn resistance to N. benthamiana, with a lower H2O2 concentration after Ppn inoculation. Further investigation of the role of NHX1 demonstrated that transient overexpression of NbNHX1 improved the vacuolar pH and cellular ROS level in N. benthamiana, which was coupled with an enlarged NAD(P) (H) pool and higher expression of ROS-responsive genes. In contrast, NbNHX1 silencing led to a lower pH in the vacuole and a lower cellular ROS level in N. benthamiana, which was coupled with a decreased NAD(P) (H) pool and decreased expression of ROS-responsive genes. These results suggest that NHX1 is involved in plant disease defence; and regulation of vacuolar pH by NHX1, affecting the cellular oxidation state, primes the antioxidative system which is associated with Ppn resistance in tobacco.

Genome-wide analysis of the AP2/ERF transcription factor superfamily in Chinese cabbage (Brassica rapa ssp. pekinensis)

Background

Chinese cabbage (Brassica rapa ssp. pekinensis) is a member of one of the most important leaf vegetables grown worldwide, which has experienced thousands of years in cultivation and artificial selection. The entire Chinese cabbage genome sequence, and more than forty thousand proteins have been obtained to date. The genome has undergone triplication events since its divergence from Arabidopsis thaliana (13 to 17 Mya), however a high degree of sequence similarity and conserved genome structure remain between the two species. Arabidopsis is therefore a viable reference species for comparative genomics studies. Variation in the number of members in gene families due to genome triplication may contribute to the broad range of phenotypic plasticity, and increased tolerance to environmental extremes observed in Brassica species. Transcription factors are important regulators involved in plant developmental and physiological processes. The AP2/ERF proteins, one of the most important families of transcriptional regulators, play a crucial role in plant growth, and in response to biotic and abiotic stressors. Our analysis will provide resources for understanding the tolerance mechanisms in Brassica rapa ssp. pekinensis.

Results

In the present study, 291 putative AP2/ERF transcription factor proteins were identified from the Chinese cabbage genome database, and compared with proteins from 15 additional species. The Chinese cabbage AP2/ERF superfamily was classified into four families, including AP2, ERF, RAV, and Soloist. The ERF family was further divided into DREB and ERF subfamilies. The AP2/ERF superfamily was subsequently divided into 15 groups. The identification, classification, phylogenetic reconstruction, conserved motifs, chromosome distribution, functional annotation, expression patterns, and interaction networks of the AP2/ERF transcription factor superfamily were predicted and analyzed. Distribution mapping results showed AP2/ERF superfamily genes were localized on the 10 Chinese cabbage chromosomes. AP2/ERF transcription factor expression levels exhibited differences among six tissue types based on expressed sequence tags (ESTs). In the AP2/ERF superfamily, 214 orthologous genes were identified between Chinese cabbage and Arabidopsis. Orthologous gene interaction networks were constructed, and included seven CBF and four AP2 genes, primarily involved in cold regulatory pathways and ovule development, respectively.

Conclusions

The evolution of the AP2/ERF transcription factor superfamily in Chinese cabbage resulted from genome triplication and tandem duplications. A comprehensive analysis of the physiological functions and biological roles of AP2/ERF superfamily genes in Chinese cabbage is required to fully elucidate AP2/ERF, which provides us with rich resources and opportunities to understand crop stress tolerance mechanisms.

Three ERF transcription factors from Chinese wild grapevine Vitis pseudoreticulata participate in different biotic and abiotic stress-responsive pathways

Ethylene response factor (ERF) functions as an important plant-specific transcription factor in regulating biotic and abiotic stress response through interaction with various stress pathways. We previously obtained three ERF members, VpERF1, VpERF2, and VpERF3 from a highly powdery mildew (PM)-resistant Chinese wild Vitis pseudoreticulata cDNA full-length library. To explore their functions associated with plant disease resistance or biotic stress, we report here to characterize three ERF members from this library. PM-inoculation analysis on three different resistant grapevine genotypes revealed that three VpERFs displayed significant responses, but a different expression pattern. Over-expression of VpERF1, VpERF2, and VpERF3 in transgenic tobacco plants demonstrated that VpERF2 and VpERF3 enhanced resistance to both bacterial pathogen Ralstonia solanacearum and fungal pathogen Phytophtora parasitica var. nicotianae Tucker. Importantly, VpERF1-overexpressing transgenic Arabidopsis plants increased susceptibility toward these pathogens. Investigation on drought, cold, and heat treatments suggested, VpERF2 was distinctly induced, whereas VpERF3 displayed a very weak response and VpERF1 was distinctly induced by drought and heat. Concurrently, VpERF3 was significantly induced by salicylic acid (SA), methyl jasmonate (MeJA), and ET. Our results showed that the three VpERFs from Chinese wild V. pseudoreticulata play different roles in either preventing disease progression via regulating the expression of relevant defense genes, or directly involving abiotic stress responsive pathways.

Putative genes involved in saikosaponin biosynthesis in Bupleurum species

Alternative medicinal agents, such as the herb Bupleurum, are increasingly used in modern medicine to supplement synthetic drugs. First, we present a review of the currently known effects of triterpene saponins-saikosaponins of Bupleurum species. The putative biosynthetic pathway of saikosaponins in Bupleurum species is summarized, followed by discussions on identification and characterization of genes involved in the biosynthesis of saikosaponins. The purpose is to provide a brief review of gene extraction, functional characterization of isolated genes and assessment of expression patterns of genes encoding enzymes in the process of saikosaponin production in Bupleurum species, mainly B. kaoi. We focus on the effects of MeJA on saikosaponin production, transcription patterns of genes involved in biosynthesis and on functional depiction.

Improved nutritive quality and salt resistance in transgenic maize by simultaneously overexpression of a natural lysine-rich protein gene, SBgLR, and an ERF transcription factor gene, TSRF1

Maize (Zea mays L.), as one of the most important crops in the world, is deficient in lysine and tryptophan. Environmental conditions greatly impact plant growth, development and productivity. In this study, we used particle bombardment mediated co-transformation to obtain marker-free transgenic maize inbred X178 lines harboring a lysine-rich protein gene SBgLR from potato and an ethylene responsive factor (ERF) transcription factor gene, TSRF1, from tomato. Both of the target genes were successfully expressed and showed various expression levels in different transgenic lines. Analysis showed that the protein and lysine content in T1 transgenic maize seeds increased significantly. Compared to non-transformed maize, the protein and lysine content increased by 7.7% to 24.38% and 8.70% to 30.43%, respectively. Moreover, transgenic maize exhibited more tolerance to salt stress. When treated with 200 mM NaCl for 48 h, both non-transformed and transgenic plant leaves displayed wilting and losing green symptoms and dramatic increase of the free proline contents. However, the degree of control seedlings was much more serious than that of transgenic lines and much more increases of the free proline contents in the transgenic lines than that in the control seedlings were observed. Meanwhile, lower extent decreases of the chlorophyll contents were detected in the transgenic seedlings. Quantitative RT-PCR was performed to analyze the expression of ten stress-related genes, including stress responsive transcription factor genes, ZmMYB59 and ZmMYC1, proline synthesis related genes, ZmP5CS1 and ZmP5CS2, photosynthesis-related genes, ZmELIP, ZmPSI-N, ZmOEE, Zmrbcs and ZmPLAS, and one ABA biosynthesis related gene, ZmSDR. The results showed that with the exception of ZmP5CS1 and ZmP5CS2 in line 9-10 and 19-11, ZmMYC1 in line 19-11 and ZmSDR in line 19-11, the expression of other stress-related genes were inhibited in transgenic lines under normal conditions. After salt treatment, the expressions of the ten stress-related genes were significantly induced in both wild-type (WT) and transgenic lines. However, compared to WT, the increases of ZmP5CS1 in all these three transgenic lines and ZmP5CS2 in line 9-10 were less than WT plants. This study provides an effective approach of maize genetic engineering for improved nutritive quality and salt tolerance.

Jacalin domain in wheat jasmonate-regulated protein Ta-JA1 confers agglutinating activity and pathogen resistance

Ta-JA1 is a jacalin-like lectin from wheat (Triticum aestivum) plants. To date, its homologs are only observed in the Gramineae family. Our previous experiments have demonstrated that Ta-JA1 contains a modular structure consisting of an N-terminal dirigent domain and a C-terminal jacalin-related lectin domain (JRL) and this protein exhibits a mannose-specific lectin activity. The over-expression of Ta-JA1 gene provides transgenic plants a broad-spectrum resistance to diseases. Here, we report the differential activities of the dirigent and JRL domains of Ta-JA1. In vitro assay showed that the recombinant JRL domain could effectively agglutinate rabbit erythrocytes and pathogen bacteria Pseudomonas syringe pv tabaci. These hemagglutination activities could be inhibited by mannose but not by galactose. In contrast, the recombinant dirigent domain did not show agglutination activity. Corresponding to these differentiations of activities, similar to full-length of Ta-JA1, the over-expression of JRL domain in transgenic plants also increased resistance to the infection of P. syringe. Unlike JRL, the over-expression of dirigent domain in transgenic plants led to alteration of the seedling sensitivity to salts. In addition, a d(N)/d(S) ratio analysis of Ta-JA1 and its related proteins showed that this protein family functionally limited to a few crop plants, such as maize, rice and wheat.

Use of the cryptogein gene to stimulate the accumulation of Bacopa saponins in transgenic Bacopa monnieri plants

Genetic transformation of the Indian medicinal plant, Bacopa monnieri, using a gene encoding cryptogein, a proteinaceous elicitor, via Ri and Ti plasmids, were established and induced bioproduction of bacopa saponins in crypt-transgenic plants were obtained. Transformed roots obtained with A. rhizogenes strain LBA 9402 crypt on selection medium containing kanamycin (100 mg l(-1)) dedifferentiated forming callus and redifferentiated to roots which, spontaneously showed shoot bud induction. Ri crypt-transformed plants thus obtained showed integration and expression of rol genes as well as crypt gene. Ti crypt-transformed B. monnieri plants were established following transformation with disarmed A. tumefaciens strain harboring crypt. Transgenic plants showed significant enhancement in growth and bacopa saponin content. Bacopasaponin D (1.4-1.69 %) was maximally enhanced in transgenic plants containing crypt. In comparison to Ri-transformed plants, Ri crypt-transformed plants showed significantly (p ≤ 0.05) enhanced accumulation of bacoside A(3), bacopasaponin D, bacopaside II, bacopaside III and bacopaside V. Produced transgenic lines can be used for further research on elicitation in crypt-transgenic plants as well as for large scale production of saponins. Key message The cryptogein gene, which encodes a proteinaceous elicitor is associated with increase in secondary metabolite accumulation-either alone or in addition to the increases associated with transformation by A. rhizogenes.

Transcriptome analysis of Nicotiana tabacum infected by Cucumber mosaic virus during systemic symptom development

Virus infection of plants may induce a variety of disease symptoms. However, little is known about the molecular mechanism of systemic symptom development in infected plants. Here we performed the first next-generation sequencing study to identify gene expression changes associated with disease development in tobacco plants (Nicotiana tabacum cv. Xanthi nc) induced by infection with the M strain of Cucumber mosaic virus (M-CMV). Analysis of the tobacco transcriptome by RNA-Seq identified 95,916 unigenes, 34,408 of which were new transcripts by database searches. Deep sequencing was subsequently used to compare the digital gene expression (DGE) profiles of the healthy plants with the infected plants at six sequential disease development stages, including vein clearing, mosaic, severe chlorosis, partial and complete recovery, and secondary mosaic. Thousands of differentially expressed genes were identified, and KEGG pathway analysis of these genes suggested that many biological processes, such as photosynthesis, pigment metabolism and plant-pathogen interaction, were involved in systemic symptom development. Our systematic analysis provides comprehensive transcriptomic information regarding systemic symptom development in virus-infected plants. This information will help further our understanding of the detailed mechanisms of plant responses to viral infection.

Molecular characterization of two ethylene response factor genes in sweetpotato that respond to stress and activate the expression of defense genes in tobacco leaves

Two ethylene response factor (ERF) genes, IbERF1 and IbERF2, were isolated from a library of expressed sequence tags (EST) prepared from suspension-cultured cells and dehydration-treated fibrous roots of sweetpotato (Ipomoea batatas). The deduced IbERFs contained a nuclear localization signal and the AP2/ERF DNA-binding domain. RT-PCR analysis revealed that IbERF1 was expressed abundantly during the growth of suspension-cultured cells, whereas the expression levels of IbERF2 transcripts were high in fibrous, thick pigmented roots. Two ERF genes also showed different responses to various types of abiotic stress and pathogen infection. Transient expression of the two ERF genes in tobacco (Nicotiana tabacum) leaves resulted in increased transcript levels of the pathogenesis-related 5 (PR5) gene, the early response to dehydration ten gene (ERD10), the CuZn superoxide dismutase gene (CuZnSOD) and the catalase gene (CAT). It is suggested that the two ERF genes play roles in the stress defense-signaling pathway as transcriptional regulators of the PR5, ERD10, CuZnSOD and CAT genes.

The rice ERF transcription factor OsERF922 negatively regulates resistance to Magnaporthe oryzae and salt tolerance

Rice OsERF922, encoding an APETELA2/ethylene response factor (AP2/ERF) type transcription factor, is rapidly and strongly induced by abscisic acid (ABA) and salt treatments, as well as by both virulent and avirulent pathovars of Magnaporthe oryzae, the causal agent of rice blast disease. OsERF922 is localized to the nucleus, binds specifically to the GCC box sequence, and acts as a transcriptional activator in plant cells. Knockdown of OsERF922 by means of RNAi enhanced resistance against M. oryzae. The elevated disease resistance of the RNAi plants was associated with increased expression of PR, PAL, and the other genes encoding phytoalexin biosynthetic enzymes and without M. oryzae infection. In contrast, OsERF922-overexpressing plants showed reduced expression of these defence-related genes and enhanced susceptibility to M. oryzae. In addition, the OsERF922-overexpressing lines exhibited decreased tolerance to salt stress with an increased Na(+)/K(+) ratio in the shoots. The ABA levels were found increased in the overexpressing lines and decreased in the RNAi plants. Expression of the ABA biosynthesis-related genes, 9-cis-epoxycarotenoid dioxygenase (NCED) 3 and 4, was upregulated in the OsERF922-overexpressing plants, and NCED4 was downregulated in the RNAi lines. These results suggest that OsERF922 is integrated into the cross-talk between biotic and abiotic stress-signalling networks perhaps through modulation of the ABA levels.

The interaction of plant biotic and abiotic stresses: from genes to the field

Plant responses to different stresses are highly complex and involve changes at the transcriptome, cellular, and physiological levels. Recent evidence shows that plants respond to multiple stresses differently from how they do to individual stresses, activating a specific programme of gene expression relating to the exact environmental conditions encountered. Rather than being additive, the presence of an abiotic stress can have the effect of reducing or enhancing susceptibility to a biotic pest or pathogen, and vice versa. This interaction between biotic and abiotic stresses is orchestrated by hormone signalling pathways that may induce or antagonize one another, in particular that of abscisic acid. Specificity in multiple stress responses is further controlled by a range of molecular mechanisms that act together in a complex regulatory network. Transcription factors, kinase cascades, and reactive oxygen species are key components of this cross-talk, as are heat shock factors and small RNAs. This review aims to characterize the interaction between biotic and abiotic stress responses at a molecular level, focusing on regulatory mechanisms important to both pathways. Identifying master regulators that connect both biotic and abiotic stress response pathways is fundamental in providing opportunities for developing broad-spectrum stress-tolerant crop plants.

Functions and application of the AP2/ERF transcription factor family in crop improvement

Plants have acquired sophisticated stress response systems to adapt to changing environments. It is important to understand plants' stress response mechanisms in the effort to improve crop productivity under stressful conditions. The AP2/ERF transcription factors are known to regulate diverse processes of plant development and stress responses. In this study, the molecular characteristics and biological functions of AP2/ERFs in a variety of plant species were analyzed. AP2/ERFs, especially those in DREB and ERF subfamilies, are ideal candidates for crop improvement because their overexpression enhances tolerances to drought, salt, freezing, as well as resistances to multiple diseases in the transgenic plants. The comprehensive analysis of physiological functions is useful in elucidating the biological roles of AP2/ERF family genes in gene interaction, pathway regulation, and defense response under stress environments, which should provide new opportunities for the crop tolerance engineering.