Genome-wide analyses of direct target genes of an ERF11 transcription factor involved in plant defense against bacterial pathogens

DeepCBA: A deep learning framework for gene expression prediction in maize based on DNA sequences and chromatin interactions

Chromatin interactions create spatial proximity between distal regulatory elements and target genes in the genome, which has an important impact on gene expression, transcriptional regulation, and phenotypic traits. To date, several methods have been developed for predicting gene expression. However, existing methods do not take into consideration the effect of chromatin interactions on target gene expression, thus potentially reducing the accuracy of gene expression prediction and mining of important regulatory elements. In this study, we developed a highly accurate deep learning-based gene expression prediction model (DeepCBA) based on maize chromatin interaction data. Compared with existing models, DeepCBA exhibits higher accuracy in expression classification and expression value prediction. The average Pearson correlation coefficients (PCCs) for predicting gene expression using gene promoter proximal interactions, proximal-distal interactions, and both proximal and distal interactions were 0.818, 0.625, and 0.929, respectively, representing an increase of 0.357, 0.16, and 0.469 over the PCCs obtained with traditional methods that use only gene proximal sequences. Some important motifs were identified through DeepCBA; they were enriched in open chromatin regions and expression quantitative trait loci and showed clear tissue specificity. Importantly, experimental results for the maize flowering-related gene ZmRap2.7 and the tillering-related gene ZmTb1 demonstrated the feasibility of DeepCBA for exploration of regulatory elements that affect gene expression. Moreover, promoter editing and verification of two reported genes (ZmCLE7 and ZmVTE4) demonstrated the utility of DeepCBA for the precise design of gene expression and even for future intelligent breeding. DeepCBA is available at http://www.deepcba.com/ or http://124.220.197.196/.

CaERF1- mediated ABA signal positively regulates camptothecin biosynthesis by activating the iridoid pathway in Camptotheca acuminata

Camptotheca acuminata is one of the primary sources of camptothecin (CPT), which is widely used in the treatment of human malignancies because of its inhibitory activity against DNA topoisomerase I. Although several transcription factors have been identified for regulating CPT biosynthesis in other species, such as Ophiorrhiza pumila, the specific regulatory components controlling CPT biosynthesis in C. acuminata have yet to be definitively determined. In this study, CaERF1, an DREB subfamily of the APETALA2/ethylene response factors (AP2ERFs), was identified in C. acuminata. The transient overexpression and silencing of CaERF1 in C. acuminata leaves confirmed that it positively regulates the accumulation of CPT by inducing the expression of CaCYC1 and CaG8O in the iridoid pathway. Results of transient transcriptional activity assay and yeast one-hybrid assays have showed that CaERF1 transcriptionally activates the expression of CaCYC1 and CaG8O by binding to RAA and CEI elements in the promoter regions of these two genes. Furthermore, the expression of CaCYC1 and CaG8O in CaERF1-silenced leaves was less sensitive to ABA treatment, indicating that CaERF1 is a crucial component involved in ABA-regulated CPT biosynthesis in C. acuminata.

NtERF4 promotes the biosynthesis of chlorogenic acid and flavonoids by targeting PAL genes in Nicotiana tabacum

Chlorogenic acid (CGA) and flavonoids are important secondary metabolites, which modulate plant growth and development, and contribute to plant resistance to various environmental stresses. ERF4 has been shown to be a repressor of anthocyanin accumulation in grape, but its full roles in regulating the biosynthesis of other phenylpropanoid compounds still needs to be further studied. In the present study, two NtERF4 genes were identified from N. tabacum genome. The expression level of NtERF4a was higher than that of NtERF4b in all the tobacco tissues examined. Over-expression of NtERF4a significantly promoted the accumulation of CGA and flavonoids in tobacco leaves, while silencing of NtERF4a significantly repressed the biosynthesis of CGA and flavonoids. RNA-seq analysis of NtERF4a-OE and WT plants revealed 8 phenylpropanoids-related differentially expressed genes (DEGs), including 4 NtPAL genes that encode key enzymes in the phenylpropanoid pathway. Activation of NtERF4a-GR fusion protein in tobacco significantly induced the transcription of NtPAL1 and NtPAL2 in the presence of protein synthesis inhibitor. Chromatin immunoprecipitation and Dual-Luc assays further indicated that NtERF4a could bind to the GCC box presented in the promoters of NtPAL1 and NtPAL2, thereby activating their transcription. Moreover, ectopic expression of NtERF4a induced the transcription of NtGSK1, NtMYC2, and NtJAZ3 genes, and enhanced the resistance of tobacco seedlings to salt and drought stresses, indicating multiple roles of NtERF4a in plants. Our findings revealed new roles of NtERF4a in modulating the accumulation of phenylpropanoid compounds in tobacco, and provided a putative target for improving phenylpropanoids synthesis and stress resistance in plants.

Transcriptomic Analysis Revealed Key Defense Genes and Signaling Pathways Mediated by the Arabidopsis thaliana Gene SAD2 in Response to Infection with Pseudomonas syringae pv. Tomato DC3000

Nucleocytoplasmic transport receptors play key roles in the nuclear translocation of disease resistance proteins, but the associated mechanisms remain unclear. The Arabidopsis thaliana gene SAD2 encodes an importin β-like protein. A transgenic Arabidopsis line overexpressing SAD2 (OESAD2/Col-0) showed obvious resistance to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) compared to the wild type (Col-0), but the knockout mutant sad2-5 was susceptible. Transcriptomic analysis was then performed on Col-0, OESAD2/Col-0, and sad2-5 leaves at 0, 1, 2, and 3 days post-inoculation with Pst DC3000. A total of 1825 differentially expressed genes (DEGs) were identified as putative biotic stress defense genes regulated by SAD2, 45 of which overlapped between the SAD2 knockout and overexpression datasets. Gene Ontology (GO) analysis indicated that the DEGs were broadly involved in single-organism cellular metabolic processes and in response to stimulatory stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) biochemical pathway analysis revealed that many of the DEGs were associated with the biosynthesis of flavonoids and other specialized metabolites. Transcription factor analysis showed that a large number of ERF/AP2, MYB, and bHLH transcription factors were involved in SAD2-mediated plant disease resistance. These results provide a basis for future exploration of the molecular mechanisms associated with SAD2-mediated disease resistance and establish a set of key candidate disease resistance genes.

Integrated metabolome and transcriptome analysis reveals salicylic acid and flavonoid pathways' key roles in cabbage's defense responses to Xanthomonas campestris pv. campestris

Xanthomonas campestris pv. campestris (Xcc) is a vascular bacteria pathogen causing black rot in cabbage. Here, the resistance mechanisms of cabbage against Xcc infection were explored by integrated metabolome and transcriptome analysis. Pathogen perception, hormone metabolisms, sugar metabolisms, and phenylpropanoid metabolisms in cabbage were systemically re-programmed at both transcriptional and metabolic levels after Xcc infection. Notably, the salicylic acid (SA) metabolism pathway was highly enriched in resistant lines following Xcc infection, indicating that the SA metabolism pathway may positively regulate the resistance of Xcc. Moreover, we also validated our hypothesis by showing that the flavonoid pathway metabolites chlorogenic acid and caffeic acid could effectively inhibit the growth of Xcc. These findings provide valuable insights and resource datasets for further exploring Xcc-cabbage interactions and help uncover molecular breeding targets for black rot-resistant varieties in cabbage.

Expression of an Antiviral Gene GmRUN1 from Soybean Is Regulated via Intron-Mediated Enhancement (IME)

Most of R (resistance) genes encode the protein containing NBS-LRR (nucleotide binding site and leucine-rich repeat) domains. Here, N. benthamiana plants were used for transient expression assays at 3-4 weeks of age. We identified a TNL (TIR-NBS-LRR) encoding gene GmRUN1 that was resistant to both soybean mosaic virus (SMV) and tobacco mosaic virus (TMV). Truncation analysis indicated the importance of all three canonical domains for GmRUN1-mediated antiviral activity. Promoter-GUS analysis showed that GmRUN1 expression is inducible by both salicylic acid (SA) and a transcription factor GmDREB3 via the cis-elements as-1 and ERE (ethylene response element), which are present in its promoter region. Interestingly, GmRUN1 gDNA (genomic DNA) shows higher viral resistance than its cDNA (complementary DNA), indicating the existence of intron-mediated enhancement (IME) for GmRUN1 regulation. We provided evidence that intron2 of GmRUN1 increased the mRNA level of native gene GmRUN1, a soybean antiviral gene SRC7 and also a reporter gene Luciferase, indicating the general transcriptional enhancement of intron2 in different genes. In summary, we identified an antiviral TNL type soybean gene GmRUN1, expression of which was regulated at different layers. The investigation of GmRUN1 gene regulatory network would help to explore the mechanism underlying soybean-SMV interactions.

Association Mapping of Verticillium Wilt Disease in a Worldwide Collection of Cotton (Gossypium hirsutum L.)

Cotton (Gossypium spp.) is the best plant fiber source in the world and provides the raw material for industry. Verticillium wilt caused by Verticillium dahliae Kleb. is accepted as a major disease of cotton production. The most practical way to deal with verticillium wilt is to develop resistant/tolerant varieties after cultural practices. One of the effective selections in plant breeding is the use of marker-assisted selection (MAS) via quantitative trait loci (QTL). Therefore, in this study, we aimed to discover the genetic markers associated with the disease. Through the association mapping analysis, common single nucleotide polymorphism (SNP) markers were obtained using 4730 SNP alleles. As a result, twenty-three markers were associated with defoliating (PYDV6 isolate) pathotype, twenty-one markers with non-defoliating (Vd11 isolate) pathotype, ten QTL with Disease Severity Index (DSI) of the leaves at the 50–60% boll opening period and eight markers were associated with DSI in the stem section. Some of the markers that show significant associations are located on protein coding genes such as protein Mpv17-like, 21 kDa protein-like, transcription factor MYB113-like, protein dehydration-induced 19 homolog 3-like, F-box protein CPR30-like, extracellular ribonuclease LE-like, putative E3 ubiquitin-protein ligase LIN, pentatricopeptide repeat-containing protein At3g62890-like, fructose-1,6-bisphosphatase, tubby-like F-box protein 8, endoglucanase 16-like, glucose-6-phosphate/phosphate translocator 2, metal tolerance protein 11-like, VAN3-binding protein-like, transformation/transcription domain-associated protein-like, pyruvate kinase isozyme A, ethylene-responsive transcription factor CRF2-like, molybdate transporter 2-like, IRK-interacting protein-like, glycosylphosphatidylinositol anchor attachment 1 protein, U3 small nucleolar RNA-associated protein 4-like, microtubule-associated protein futsch-like, transport and Golgi organization 2 homolog, splicing factor 3B subunit 3-like, mediator of RNA polymerase II transcription subunit 15a-like, putative ankyrin repeat protein, and protein networked 1D-like. It has been reported in previous studies that most of these genes are associated with biotic and abiotic stress factors. As a result, once validated, it would be possible to use the markers obtained in the study in Marker Assisted Selection (MAS) breeding.