A novel transcription factor JcNAC1 response to stress in new model woody plant Jatropha curcas

Co-Expression of JcNAC1- and JcZFP8-Improved Agronomic Traits of Tobacco and Enhanced Drought Resistance through NbbHLH1 and NbbHLH2

Previous studies have identified numerous transcription factors involved in drought response, each of which play different roles in plants. The objective of the present study was to evaluate the effectiveness of two transcription factors on drought response in Jatropha curcas L., JcNAC1 and JcZFP8. The overexpression of these transcription factors in tobacco (Nicotiana benthamiana L.) improved drought resistance, but JcZFP8 delayed germination and JcNAC1 reduced biomass and yield. By constitutively co-expressing these two genes in tobacco, drought resistance was improved, and the negative effects of each of them were overcome. The transgenic plants with double-gene co-expression showed stronger drought tolerance with 1.76-fold greater accumulation of proline and lower H2O2 and malondialdehyde (MDA) content to 43 and 65% of wildtype (WT) levels, respectively. The expression levels of NbbHLH1 and NbbHLH2 genes upregulated linearly with the increased drought tolerance of double genes co-expression plants. In drought conditions, the leaf water contents of bhlh1, bhlh2, and bhlh1bhlh2 deletion mutants obtained by CRISPR-CAS9 knockout technique were maintained at 99%, 97%, and 97% of WT. The bhlh1bhlh2 was found with lower germination rate but with higher reactive oxygen levels (1.64-fold H2O2 and 1.41-fold MDA levels). Thus, the co-expression of two transcription factors with different functions overcame the adverse traits brought by a single gene and enhanced the shared drought-tolerant traits, which can provide guidance on theory and selection of gene combinations for the application of multi-gene co-expression in agriculture in the future.

Identification of Pepper CaSBP08 Gene in Defense Response Against Phytophthora capsici Infection

Little information is available on the role of Squamosa promoter binding protein (SBP)-box genes in pepper plants. This family of genes is known to have transcription characteristics specific to plants and to regulate plant growth, development, stress responses, and signal transduction. To investigate their specific effects in pepper (Capsicum annuum), we screened pepper SBP-box family genes (CaSBP genes) for Phytophthora capsici (P. capsici) resistance genes using virus-induced gene silencing. CaSBP08, CaSBP11, CaSBP12, and CaSBP13, which are associated with plant defense responses against P. capsici, were obtained from among fifteen identified CaSBP genes. The function of CaSBP08 was identified in pepper defense response against P. capsici infection in particular. CaSBP08 protein was localized to the nucleus. Silencing of CaSBP08 enhanced resistance to P. capsici infection. Following P. capsici inoculation, the malondialdehyde content, peroxidase activity, and disease index percentage of the CaSBP08-silenced plants decreased compared to the control. Additionally, the expression levels of other defense-related genes, especially those of CaBPR1 and CaSAR8.2, were more strongly induced in CaSBP08-silenced plants than in the control. However, CaSBP08 overexpression in Nicotiana benthamiana enhanced susceptibility to P. capsici infection. This work provides a foundation for the further research on the role of CaSBP genes in plant defense responses against P. capsici infection.

JCDB: a comprehensive knowledge base for Jatropha curcas, an emerging model for woody energy plants

Background

Jatropha curcas is an oil-bearing plant, and has seeds with high oil content (~ 40%). Several advantages, such as easy genetic transformation and short generation duration, have led to the emergence of J. curcas as a model for woody energy plants. With the development of high-throughput sequencing, the genome of Jatropha curcas has been sequenced by different groups and a mass of transcriptome data was released. How to integrate and analyze these omics data is crucial for functional genomics research on J. curcas.

Results

By establishing pipelines for processing novel gene identification, gene function annotation, and gene network construction, we systematically integrated and analyzed a series of J. curcas transcriptome data. Based on these data, we constructed a J. curcas database (JCDB), which not only includes general gene information, gene functional annotation, gene interaction networks, and gene expression matrices but also provides tools for browsing, searching, and downloading data, as well as online BLAST, the JBrowse genome browser, ID conversion, heatmaps, and gene network analysis tools.

Conclusions

JCDB is the most comprehensive and well annotated knowledge base for J. curcas. We believe it will make a valuable contribution to the functional genomics study of J. curcas. The database is accessible at http://jcdb.xtbg.ac.cn.

Ammopiptanthus mongolicus stress-responsive NAC gene enhances the tolerance of transgenic Arabidopsis thaliana to drought and cold stresses

Drought and cold are the primary factors limiting plant growth worldwide. The Ammopiptanthus mongolicus NAC11 (AmNAC11) gene encodes a stress-responsive transcription factor. Expression of the AmNAC11 gene was induced by drought, cold and high salinity. The AmNAC11 protein was localized in the nucleus and plays an important role in tolerance to drought, cold and salt stresses. We also found that differential expression of AmNAC11 was induced in the early stages of seed germination and was related to root growth. When the AmNAC11 gene was introduced into Arabidopsis thaliana by an Agrobacterium-mediated method, the transgenic lines expressing AmNAC11 displayed significantly enhanced tolerance to drought and freezing stresses compared to wild-type Arabidopsis thaliana plants. These results indicated that over-expression of the AmNAC11 gene in Arabidopsis could significantly enhance its tolerance to drought and freezing stresses. Our study provides a promising approach to improve the tolerance of crop cultivars to abiotic stresses through genetic engineering.

Functional Identification of Corynespora cassiicola-Responsive miRNAs and Their Targets in Cucumber

Target leaf spot (TLS), which is caused by Corynespora cassiicola (C. cassiicola), is one of the most important diseases in cucumber (Cucumis sativus L.). Our previous research identified several C. cassiicola-responsive miRNAs in cucumber by high-throughput sequencing, including two known miRNAs and two novel miRNAs. The target genes of these miRNAs were related to secondary metabolism. In this study, we verified the interaction between these miRNAs and target genes by histochemical staining and fluorescence quantitative assays of GUS. We transiently expressed the candidate miRNAs and target genes in cucumber cotyledons to investigate the resistance to C. cassiicola. Transient expression of miR164d, miR396b, Novel-miR1, and Novel-miR7 in cucumber resulted in decreased resistance to C. cassiicola, while transient expression of NAC (inhibited by miR164d), APE (inhibited by miR396b), 4CL (inhibited by Novel-miR1), and PAL (inhibited by Novel-miR7) led to enhanced resistance to C. cassiicola. In addition, overexpression of 4CL and PAL downregulated lignin synthesis, and overexpression of Novel-miR1 and Novel-miR7 also downregulated lignin synthesis, indicating that the regulation of 4CL and PAL by Novel-miR1 and Novel-miR7 could affect lignin content. The tobacco rattle virus (TRV) induced short tandem target mimic (STTM)-miRNA silencing vector was successfully constructed, and target miRNAs were successfully silenced. The identification of disease resistance and lignin content showed that silencing candidate miRNAs could improve cucumber resistance to C. cassiicola.

A Novel Transcription Factor CaSBP12 Gene Negatively Regulates the Defense Response against Phytophthora capsici in Pepper (Capsicum annuum L.)

SBP-box (Squamosa-promoter binding protein) genes are a type of plant-specific transcription factor and play important roles in plant growth, signal transduction and stress response. However, little is known about the SBP-box genes in pepper (CaSBP), especially in the process of Phytophthora capsici infection. In this study, a novel gene (CaSBP12) was selected from the CaSBP gene family, which was isolated from the pepper genome database in our previous study. The CaSBP12 gene was located in the nucleus of the cell and its silencing in the pepper plant enhanced the defense response against Phytophthora capsici infection. After inoculation with Phytophthora capsici, the root activity of the CaSBP12-silenced plants is compared to control plants, while malondialdehyde (MDA) content is compared viceversa. Additionally, the expression of defense related genes (CaPO1, CaSAR8.2, CaBPR1, and CaDEF1) in the silenced plants were induced to different degrees and the peak of CaSAR8.2 and CaBPR1 were higher than that of CaDEF1. The CaSBP12 over-expressed Nicotiana benthamiana plants were more susceptible to Phytophthora capsici infection with higher EC (electrical conductivity) and MDA contents as compared to the wild-type. The relative expression of defense related genes (NbDEF, NbNPR1, NbPR1a, and NbPR1b) in transgenic and wild-type Nicotiana benthamiana plants were induced, especially the NbPR1a and NbPR1b. In conclusion, these results indicate that CaSBP12 gene negative regulates the defense response against Phytophthora capsici infection which suggests their potentially significant role in plant defense. To our knowledge, this is the first report on CaSBP gene which negative regulate defense response.

Transcriptome and miRNA analyses of the response to Corynespora cassiicola in cucumber

Cucumber (Cucumis sativus L.) target leaf spot (TLS), which is caused by the fungus Corynespora cassiicola (C. cassiicola), seriously endangers the production of cucumber. In this assay, we performed comprehensive sequencing of the transcriptome and microRNAs (miRNAs) of a resistant cucumber (Jinyou 38) during C. cassiicola inoculation using the Illumina NextSeq 500 platform. The possible genes related to the response to C. cassiicola were associated with plant hormones, transcription factors, primary metabolism, Ca²⁺ signaling pathways, secondary metabolism and defense genes. In total, 150 target genes of these differentially expressed miRNAs were predicted by the bioinformatic analysis. By analyzing the function of the target genes, several candidate miRNAs that may be related to the response to C. cassiicola stress were selected. We also predicted 7 novel miRNAs and predicted their target genes. Moreover, the expression patterns of the candidate genes and miRNAs were tested by quantitative real-time RT-PCR. According to the analysis, genes and miRNAs associated with secondary metabolism, particularly the phenylpropanoid biosynthesis pathway, may play a major role in the resistance to C. cassiicola stress in cucumber. These results offer a foundation for future studies exploring the mechanism and key genes of resistance to cucumber TLS.

Isolation and characterization of the Jatropha curcas APETALA1 (JcAP1) promoter conferring preferential expression in inflorescence buds

The 1.5 kb JcAP1 promoter from the biofuel plant Jatropha curcas is predominantly active in the inflorescence buds of transgenic plants, in which the -1313/-1057 region is essential for maintaining the activity. Arabidopsis thaliana APETALA1 (AP1) is a MADS-domain transcription factor gene that functions primarily in flower development. We isolated a homolog of AP1 from Jatropha curcas (designated JcAP1), which was shown to exhibit flower-specific expression in Jatropha. JcAP1 is first expressed in inflorescence buds and continues to be primarily expressed in the sepals. We isolated a 1.5 kb JcAP1 promoter and evaluated its activity in transgenic Arabidopsis and Jatropha using the β-glucuronidase (GUS) reporter gene. In transgenic Arabidopsis and Jatropha, the inflorescence buds exhibited notable GUS activity, whereas the sepals did not. Against expectations, the JcAP1 promoter was active in the anthers of Arabidopsis and Jatropha and was highly expressed in Jatropha seeds. An analysis of promoter deletions in transgenic Arabidopsis revealed that deletion of the -1313/-1057 region resulted in loss of JcAP1 promoter activity in the inflorescence buds and increased activity in the anthers. These results suggested that some regulatory sequences in the -1313/-1057 region are essential for maintaining promoter activity in inflorescence buds and can partly suppress activity in the anthers. Based on these findings, we hypothesized that other elements located upstream of the 1.5 kb JcAP1 promoter may be required for flower-specific activation. The JcAP1 promoter characterized in this study can be used to drive transgene expression in both the inflorescence buds and seeds of Jatropha.

An efficient protocol for Agrobacterium-mediated transformation of the biofuel plant Jatropha curcas by optimizing kanamycin concentration and duration of delayed selection

Jatropha curcas is considered a potential biodiesel feedstock crop. Currently, the value of J. curcas is limited because its seed yield is generally low. Transgenic modification is a promising approach to improve the seed yield of J. curcas. Although Agrobacterium-mediated genetic transformation of J. curcas has been pursued for several years, the transformation efficiency remains unsatisfying. Therefore, a highly efficient and simple Agrobacterium-mediated genetic transformation method for J. curcas should be developed. We examined and optimized several key factors that affect genetic transformation of J. curcas in this study. The results showed that the EHA105 strain was superior to the other three Agrobacterium tumefaciens strains for infecting J. curcas cotyledons, and the supplementation of 100 mM acetosyringone slightly increased the transient transformation frequency. Use of the appropriate inoculation method, optimal kanamycin concentration and appropriate duration of delayed selection also improved the efficiency of stable genetic transformation of J. curcas. The percentage of β-glucuronidase positive J. curcas shoots reached as high as 56.0 %, and 1.70 transformants per explant were obtained with this protocol. Furthermore, we optimized the root-inducing medium to achieve a rooting rate of 84.9 %. Stable integration of the T-DNA into the genomes of putative transgenic lines was confirmed by PCR and Southern blot analysis. Using this improved protocol, a large number of transgenic J. curcas plantlets can be routinely obtained within approximately 4 months. The detailed information provided here for each step of J. curcas transformation should enable successful implementation of this transgenic technology in other laboratories.

Isolation and characterization of an ubiquitin extension protein gene (JcUEP) promoter from Jatropha curcas

The JcUEP promoter is active constitutively in the bio-fuel plant Jatropha curcas , and is an alternative to the widely used CaMV35S promoter for driving constitutive overexpression of transgenes in Jatropha. Well-characterized promoters are required for transgenic breeding of Jatropha curcas, a biofuel feedstock with great potential for production of bio-diesel and bio-jet fuel. In this study, an ubiquitin extension protein gene from Jatropha, designated JcUEP, was identified to be ubiquitously expressed. Thus, we isolated a 1.2 kb fragment of the 5' flanking region of JcUEP and evaluated its activity as a constitutive promoter in Arabidopsis and Jatropha using the β-glucuronidase (GUS) reporter gene. As expected, histochemical GUS assay showed that the JcUEP promoter was active in all Arabidopsis and Jatropha tissues tested. We also compared the activity of the JcUEP promoter with that of the cauliflower mosaic virus 35S (CaMV35S) promoter, a well-characterized constitutive promoter conferring strong transgene expression in dicot species, in various tissues of Jatropha. In a fluorometric GUS assay, the two promoters showed similar activities in stems, mature leaves and female flowers; while the CaMV35S promoter was more effective than the JcUEP promoter in other tissues, especially young leaves and inflorescences. In addition, the JcUEP promoter retained its activity under stress conditions in low temperature, high salt, dehydration and exogenous ABA treatments. These results suggest that the plant-derived JcUEP promoter could be an alternative to the CaMV35S promoter for driving constitutive overexpression of transgenes in Jatropha and other plants.