Identification of hub genes regulating isoflavone accumulation in soybean seeds via GWAS and WGCNA approaches

Isolation and identification of core-genes in barley roots under low phosphorus stress

BACKGROUND

Low phosphorus stress significantly limits plant growth and agricultural production. Identifying core genes responsive to low-phosphorus stress and breeding new high-phosphorus-efficient crop varieties are crucial for solving practical production problems. Barley is an important crop with genetic diversity and stress tolerance. In this study, we aimed to explore the core genes in barley roots under low-phosphorus stress.

METHODS AND RESULTS

Based on the transcriptome sequencing data of barley root under low phosphorus stress, we used the Weighted Gene Co-expression Network Analysis (WGCNA) method on the high phosphorus-efficient genotype GN121. All expressed genes related to phosphorus content were grouped into 16 co-expression modules. Six highly correlated modules were selected for GO enrichment analysis. Genes in the green module were significantly enriched in "response to stress" and "response to oxidative stress" signaling pathways, while genes in the turquoise module were significantly enriched in "cell response to stimulation" and "cell response to stress" pathways. Through further analysis of these two modules, we identified three core genes: endoglucan-1,3-β-glucosidase 3 (HORVU2Hr1G044440) and peroxidase 5 (HORVU1Hr1G023750 and HORVU1Hr1G016820).

CONCLUSIONS

The identified three core genes above mentioned are involved in the regulation of abiotic stress. These results offer clues for further research on the molecular mechanism of barley's response to low phosphorus stress and genetic resources for breeding high-phosphorus-efficient crop varieties. The findings contribute to understanding how barley adapts to low-phosphorus environments and provide a basis for improving crop phosphorus-use efficiency.

An R2R3-type MYB transcription factor, GmMYB77, negatively regulates isoflavone accumulation in soybean [Glycine max (L.) Merr.]

Soybean [Glycine max (L.) Merr.] is an exceptionally rich in isoflavones, and these compounds attach to oestrogen receptors in the human body, lessening the risk of breast cancer and effectively alleviating menopausal syndrome symptoms. Uncovering the molecular mechanisms that regulate soybean isoflavone accumulation is crucial for enhancing the production of these compounds. In this study, we combined bulk segregant analysis sequencing (BSA-seq) and a genome-wide association study (GWAS) to discover a novel R2R3-MYB family gene, GmMYB77, that regulates isoflavone accumulation in soybean. Using the soybean hairy root transient expression system, we verified that GmMYB77 inhibits isoflavone accumulation. Furthermore, knocking out GmMYB77 significantly increased total isoflavone (TIF) content, particularly malonylglycitin, while its overexpression resulted in a notable decrease in contents of malonylglycitin and TIF. We found that GmMYB77 can directly binds the core sequence GGT and suppresses the expression of the key isoflavone biosynthesis genes Isoflavone synthase 1 (GmIFS1), Isoflavone synthase 2 (GmIFS2), Chalcone synthase 7 (GmCHS7) and Chalcone synthase 8 (GmCHS8) by using dual-luciferase assays, electrophoretic mobility shift assays and yeast one-hybrid experiments. Natural variations in the promoter region of GmMYB77 affect its expression, thereby regulating the malonylglycitin and TIF contents. Hap-P2, an elite haplotype, plays a pivotal role in soybean breeding for substantially enhanced isoflavone content. These findings enhance our understanding of the genes influencing soybean isoflavone content and provide a valuable genetic resource for molecular breeding efforts in the future.

Transcriptome Comparison between Resistant and Susceptible Soybean Cultivars in Response to Inoculation of Phytophthora sojae

Phytophthora root and stem rot, caused by Phytophthora sojae, considerably reduces soybean yield worldwide. Our previous study identified two genomic regions on chromosome 18 (2.1-2.6 and 53.1-53.3 Mbp) that confer resistance to the P. sojae isolate 2457, through linkage analysis using progenies derived from the Daepung × Socheong2 population. These two regions contained 51 and 19 annotated genes, respectively. However, the specific gene responsible for resistance to P. sojae isolate 2457 has yet to be identified. In this study, we performed a comparative transcriptomic analysis of Socheong2 and Daepung, two Korean soybean varieties identified as resistant and susceptible to P. sojae isolate 2457, respectively. RNA sequencing was conducted on tissue samples collected at 0, 6, and 12 hours after inoculation (HAI), and significant differences in the expression of defense-related genes were observed across time points and between the two cultivars. Genes associated with the jasmonic acid, salicylic acid, ethylene, and systemic acquired resistance pathways were upregulated in both cultivars at 6 and 12 HAI compared to 0 HAI, with these biological processes were more strongly upregulated in Socheong2 compared to Daepung at 6 and 12 HAI. A comparison of differentially expressed genes (DEGs) and candidate genes within the previously identified QTL regions revealed an ortholog of the HS1 PRO-1 2 gene from Arabidopsis thaliana among the upregulated DEGs in Socheong2, particularly at 12 HAI compared to 0 HAI. This study will aid in targeted breeding efforts to develop soybean varieties with improved resistance to P. sojae.

Bioinformatics Identification and Expression Analysis of Acetyl-CoA Carboxylase Reveal Its Role in Isoflavone Accumulation during Soybean Seed Development

Isoflavones belong to the class of flavonoid compounds, which are important secondary metabolites that play a crucial role in plant development and defense. Acetyl-CoA carboxylase (ACCase) is a biotin-dependent enzyme that catalyzes the conversion of Acetyl-CoA into Malonyl-CoA in plants. It is a key enzyme in fatty acid synthesis and also catalyzes the production of various secondary metabolites. However, information on the ACC gene family in the soybean (Glycine max L. Merr.) genome and the specific members involved in isoflavone biosynthesis is still lacking. In this study, we identified 20 ACC family genes (GmACCs) from the soybean genome and further characterized their evolutionary relationships and expression patterns. Phylogenetic analysis showed that the GmACCs could be divided into five groups, and the gene structures within the same groups were highly conserved, indicating that they had similar functions. The GmACCs were randomly distributed across 12 chromosomes, and collinearity analysis suggested that many GmACCs originated from tandem and segmental duplications, with these genes being under purifying selection. In addition, gene expression pattern analysis indicated that there was functional divergence among GmACCs in different tissues. The GmACCs reached their peak expression levels during the early or middle stages of seed development. Based on the transcriptome and isoflavone content data, a weighted gene co-expression network was constructed, and three candidate genes (Glyma.06G105900, Glyma.13G363500, and Glyma.13G057400) that may positively regulate isoflavone content were identified. These results provide valuable information for the further functional characterization and application of GmACCs in isoflavone biosynthesis in soybean.

Joint GWAS and WGCNA Identify Genes Regulating the Isoflavone Content in Soybean Seeds

Isoflavone is a secondary metabolite of the soybean phenylpropyl biosynthesis pathway with physiological activity and is beneficial to human health. In this study, the isoflavone content of 205 soybean germplasm resources from 3 locations in 2020 showed wide phenotypic variation. A joint genome-wide association study (GWAS) and weighted gene coexpression network analysis (WGCNA) identified 33 single-nucleotide polymorphisms and 11 key genes associated with soybean isoflavone content. Gene ontology enrichment analysis, gene coexpression, and haplotype analysis revealed natural variations in the Glyma.12G109800 (GmOMT7) gene and promoter region, with Hap1 being the elite haplotype. Transient overexpression and knockout of GmOMT7 increased and decreased the isoflavone content, respectively, in hairy roots. The combination of GWAS and WGCNA effectively revealed the genetic basis of soybean isoflavone and identified potential genes affecting isoflavone synthesis and accumulation in soybean, providing a valuable basis for the functional study of soybean isoflavone.

Transcriptome Profiling and Weighted Gene Correlation Network Analysis Reveal Hub Genes and Pathways Involved in the Response to Polyethylene-Glycol-Induced Drought Stress of Two Citrus Rootstocks

Agriculture faces the dual challenge of increasing food production and safeguarding the environment. Climate change exacerbates this challenge, reducing crop yield and biomass due to drought stress, especially in semi-arid regions where Citrus plants are cultivated. Understanding the molecular mechanisms underlying drought tolerance in Citrus is crucial for developing adaptive strategies. Plants of two citrus rootstocks, Carrizo Citrange and Bitters (C22), were grown in aerated half-strength Hoagland's nutrient solution. Post-acclimation, the plants were exposed to a solution containing 0% (control) or 15% PEG-8000 for 10 days. Leaf malonyl dialdehyde (MDA) and hydrogen peroxide (H2O2) content were measured to assess the reached oxidative stress level. Total RNA was extracted, sequenced, and de novo-assembled. Weighted Gene Correlation Network Analysis (WGCNA) was conducted to examine the relationship between gene expression patterns and the levels of MDA and H2O2 used as oxidative stress indicators. Plant visual inspection and MDA and H2O2 contents clearly indicate that Bitters is more tolerant than Carrizo towards PEG-induced drought stress. RNA-Seq analysis revealed a significantly higher number of differentially expressed genes (DEGs) in Carrizo (6092) than in Bitters (320), with most being associated with drought sensing, ROS scavenging, osmolyte biosynthesis, and cell wall metabolism. Moreover, the WGCNA identified transcription factors significantly correlated with MDA and H2O2 levels, thus providing insights into drought-coping strategies and offering candidate genes for enhancing citrus drought tolerance.

Characterization of Mild Acid Stress Response in an Engineered Acid-Tolerant Escherichia coli Strain

Engineering acid-tolerant microbial strains is a cost-effective approach to overcoming acid stress during industrial fermentation. We previously constructed an acid-tolerant strain (Escherichia coli SC3124) with enhanced growth robustness and productivity under mildly acidic conditions by fine-tuning the expression of synthetic acid-tolerance module genes consisting of a proton-consuming acid resistance system (gadE), a periplasmic chaperone (hdeB), and ROS scavengers (sodB, katE). However, the precise acid-tolerance mechanism of E. coli SC3124 remained unclear. In this study, the growth of E. coli SC3124 under mild acid stress (pH 6.0) was determined. The final OD600 of E. coli SC3124 at pH 6.0 was 131% and 124% of that of the parent E. coli MG1655 at pH 6.8 and pH 6.0, respectively. Transcriptome analysis revealed the significant upregulation of the genes involved in oxidative phosphorylation, the tricarboxylic acid (TCA) cycle, and lysine-dependent acid-resistance system in E. coli SC3124 at pH 6.0. Subsequently, a weighted gene coexpression network analysis was performed to systematically determine the metabolic perturbations of E. coli SC3124 with mild acid treatment, and we extracted the gene modules highly associated with different acid traits. The results showed two biologically significant coexpression modules, and 263 hub genes were identified. Specifically, the genes involved in ATP-binding cassette (ABC) transporters, oxidative phosphorylation, the TCA cycle, amino acid metabolism, and purine metabolism were highly positively associated with mild acid stress responses. We propose that the overexpression of synthetic acid-tolerance genes leads to metabolic changes that confer mild acid stress resistance in E. coli. Integrated omics platforms provide valuable information for understanding the regulatory mechanisms of mild acid tolerance in E. coli and highlight the important roles of oxidative phosphorylation and ABC transporters in mild acid stress regulation. These findings offer novel insights to better the design of acid-tolerant chasses to synthesize value-added chemicals in a green and sustainable manner.

Integrated analysis of transcriptomics and defense-related phytohormones to discover hub genes conferring maize Gibberella ear rot caused by Fusarium Graminearum

BACKGROUND

Gibberella ear rot (GER) is one of the most devastating diseases in maize growing areas, which directly reduces grain yield and quality. However, the underlying defense response of maize to pathogens infection is largely unknown.

RESULTS

To gain a comprehensive understanding of the defense response in GER resistance, two contrasting inbred lines 'Nov-82' and 'H10' were used to explore transcriptomic profiles and defense-related phytohormonal alterations during Fusarium graminearum infection. Transcriptomic analysis revealed 4,417 and 4,313 differentially expressed genes (DEGs) from the Nov-82 and H10, respectively, and 647 common DEGs between the two lines. More DEGs were obviously enriched in phenylpropanoid biosynthesis, secondary metabolites biosynthesis, metabolic process and defense-related pathways. In addition, the concentration of the defense-related phytohormones, jasmonates (JAs) and salicylates (SAs), was greatly induced after the pathogen infection. The level of JAs in H10 was more higher than in Nov-82, whereas an opposite pattern for the SA between the both lines. Integrated analysis of the DEGs and the phytohormones revealed five vital modules based on co-expression network analysis according to their correlation. A total of 12 hub genes encoding fatty acid desaturase, subtilisin-like protease, ethylene-responsive transcription factor, 1-aminocyclopropane-1-carboxylate oxidase, and sugar transport protein were captured from the key modules, indicating that these genes might play unique roles in response to pathogen infection, CONCLUSIONS: Overall, our results indicate that large number DEGs related to plant disease resistance and different alteration of defensive phytohormones were activated during F. graminearum infection, providing new insight into the defense response against pathogen invasion, in addition to the identified hub genes that can be further investigated for enhancing maize GER resistance.

The effect of exogenous melatonin on waterlogging stress in Clematis

Clematis is the queen of the vines, being an ornamental plant with high economic value. Waterlogging stress reduces the ornamental value of the plant and limits its application. Melatonin plays an important role in plant resistance to abiotic stresses. In this study, the physiological responses and gene expression levels of two wild species, namely, Clematis tientaiensis and Clematis lanuginosa, and two horticultural varieties, namely, 'Sen-No-Kaze' and 'Viva Polonia,' under waterlogging stress were analyzed to determine the effect of melatonin on waterlogging tolerance. The results showed that the waterlogging tolerances of C. lanuginosa and 'Sen-No-Kaze' were relatively poor, but were significantly improved by concentrations of 100 μmol·L-1 and 50 μmol·L-1 melatonin. C. tientaiensis and 'Viva Polonia' had relatively strong tolerance to waterlogging, and this was significantly improved by 200 μmol·L-1 melatonin. Under waterlogging stress, the relative conductivity and H2O2 content of Clematis increased significantly; the photosynthetic parameters and chlorophyll contents were significantly decreased; photosynthesis was inhibited; the contents of soluble protein and soluble sugars were decreased. Effective improvement of waterlogging tolerance after exogenous melatonin spraying, the relative conductivity was decreased by 4.05%-27.44%; the H2O2 content was decreased by 3.84%-23.28%; the chlorophyll content was increased by 35.59%-103.36%; the photosynthetic efficiency was increased by 25.42%-45.86%; the antioxidant enzyme activities of APX, POD, SOD, and CAT were increased by 28.03%-158.61%; the contents of proline, soluble protein, and soluble sugars were enhanced, and cell homeostasis was improved. Transcription sequencing was performed on wild Clematis with differences in waterlogging tolerance, and nine transcription factors were selected that were highly correlated with melatonin and that had the potential to improve waterlogging tolerance, among which LBD4, and MYB4 were significantly positively correlated with the antioxidant enzyme system, and bHLH36, DOF36, and WRKY4 were significantly negatively correlated. Photosynthetic capacity was positively correlated with DOF36 and WRKY4 while being significantly negatively correlated with MYB4, MOF1, DOF47, REV1 and ABR1. Melatonin could enhance the flooding tolerance of Clematis by improving photosynthetic efficiency and antioxidant enzyme activity. This study provides an important basis and reference for the application of melatonin in waterlogging-resistant breeding of Clematis.

Cytochrome GmGLY1 is Involved in the Biosynthesis of Glycitein in Soybean

Isoflavones, the major secondary metabolites of interest due to their benefits to both human and plant health, are exclusively produced by legumes. In this study, we profiled the isoflavone content in dry seeds from 211 soybean [Glycine max (L.) Merr.] accessions grown across five environments. Broad and discernible phenotypic variations were observed among accessions, regions, and years of growth. Twenty-six single-nucleotide polymorphisms (SNPs) associated with the sum of glycitein (GLE), glycitin (GL), 6″-O-acetylglycitin (AGL), and 6″-O-malonylglycitin (MGL) contents were detected in multiple environments via a genome-wide association study (GWAS). These SNPs were located on chromosome 11 (8,148,438 bp to 8,296,956 bp, renamed qGly11-01). Glyma.11g108300 (GmGLY1), a gene that encodes a P450 family protein, was identified via sequence variation analysis, functional annotation, weighted gene coexpression network analysis (WGCNA), and expression profile analysis of candidate gene, and hairy roots transformation in soybean. Overexpression of GmGLY1 increased the glycitein content (GLC) in soybean hairy roots and transgenic seeds, while CRISPR/Cas9-generated mutants exhibited decreased GLC and increased daidzein content (DAC). Haplotype analysis revealed that GmGLY1 allelic variations significantly affect the GLC accumulation. These findings enhance our understanding of genes influencing GLC in soybean and may guide breeding for lines with high and stable GLC.

GWAS and WGCNA Analysis Uncover Candidate Genes Associated with Oil Content in Soybean

Soybean vegetable oil is an important source of the human diet. However, the analysis of the genetic mechanism leading to changes in soybean oil content is still incomplete. In this study, a total of 227 soybean materials were applied and analyzed by a genome-wide association study (GWAS). There are 44 quantitative trait nucleotides (QTNs) that were identified as associated with oil content. A total of six, four, and 34 significant QTN loci were identified in Xiangyang, Hulan, and Acheng, respectively. Of those, 26 QTNs overlapped with or were near the known oil content quantitative trait locus (QTL), and 18 new QTNs related to oil content were identified. A total of 594 genes were located near the peak single nucleotide polymorphism (SNP) from three tested environments. These candidate genes exhibited significant enrichment in tropane, piperidine, and pyridine alkaloid biosynthesiss (ko00960), ABC transporters (ko02010), photosynthesis-antenna proteins (ko00196), and betalain biosynthesis (ko00965). Combined with the GWAS and weighted gene co-expression network analysis (WGCNA), four candidate genes (Glyma.18G300100, Glyma.11G221100, Glyma.13G343300, and Glyma.02G166100) that may regulate oil content were identified. In addition, Glyma.18G300100 was divided into two main haplotypes in the studied accessions. The oil content of haplotype 1 is significantly lower than that of haplotype 2. Our research findings provide a theoretical basis for improving the regulatory mechanism of soybean oil content.

Hub Genes and Pathways Related to Lemon (Citrus limon) Leaf Response to Plenodomus tracheiphilus Infection and Influenced by Pseudomonas mediterranea Biocontrol Activity

The lemon industry in the Mediterranean basin is strongly threatened by "mal secco" disease (MSD) caused by the fungus Plenodomus tracheiphlilus. Leaf pretreatments with Pseudomonas mediterranea 3C have been proposed as innovative tools for eco-sustainable interventions aimed at controlling the disease. In this study, by exploiting the results of previously performed RNAseq analysis, WCGNA was conducted among gene expression patterns in both inoculated (Pt) and pretreated and fungus-inoculated lemon plants (Citrus limon L.) (3CPt), and two indicators of fungal infection, i.e., the amount of fungus DNA measured in planta and the disease index (DI). The aims of this work were (a) to identify gene modules significantly associated with those traits, (b) to construct co-expression networks related to mal secco disease; (c) to define the effect and action mechanisms of P. mediterranea by comparing the networks. The results led to the identification of nine hub genes in the networks, with three of them belonging to receptor-like kinases (RLK), such as HERK1, CLAVATA1 and LRR, which play crucial roles in plant-pathogen interaction. Moreover, the comparison between networks indicated that the expression of those receptors is not induced in the presence of P. mediterranea, suggesting how powerful WCGNA is in discovering crucial genes that must undergo further investigation and be eventually knocked out.

Isoflavonoid metabolism in leguminous plants: an update and perspectives

Isoflavonoids constitute a well-investigated category of phenylpropanoid-derived specialized metabolites primarily found in leguminous plants. They play a crucial role in legume development and interactions with the environment. Isoflavonoids usually function as phytoalexins, acting against pathogenic microbes in nature. Additionally, they serve as signaling molecules in rhizobial symbiosis. Notably, owing to their molecular structure resembling human estrogen, they are recognized as phytoestrogens, imparting positive effects on human health. This review comprehensively outlines recent advancements in research pertaining to isoflavonoid biosynthesis, transcriptional regulation, transport, and physiological functions, with a particular emphasis on soybean plants. Additionally, we pose several questions to encourage exploration into novel contributors to isoflavonoid metabolism and their potential roles in plant-microbe interactions.

Identification of Genes Responsible for the Synthesis of Glycitein Isoflavones in Soybean Seeds

Soybean (Glycine max (L.) Merrill) isoflavones are among the most important secondary metabolites, with functional benefits for human health. Soybeans accumulate three aglycone forms of isoflavones: genistein, daidzein, and glycitein. Soybean landrace Kumachi-1 does not accumulate malonylglycitin at all. Gene structure analysis indicated that Glyma.11G108300 (F6H4) of Kumachi-1 has a 3.8-kbp insertion, resulting in a truncated flavonoid 6-hydroxylase (F6H) sequence compared to the wild-type sequence in Fukuyutaka. Mapping experiments using a mutant line (MUT1246) with a phenotype similar to that of Kumachi-1, with a single-nucleotide polymorphism (SNP) in F6H4, revealed co-segregation of this mutation and the absence of glycitein isoflavones. We also identified a mutant line (K01) that exhibited a change in the HPLC retention time of glycitein isoflavones, accumulating glycoside and malonylglycoside forms of 6-hydroxydaidzein. K01 contains an SNP that produces a premature stop codon in Glyma.01G004200 (IOMT3), a novel soybean isoflavone O-methyltransferase (IOMT) gene. We further analyzed transgenic hairy roots of soybeans expressing Glyma.11G108300 (F6H4) and Glyma.01G004200 (IOMT3). Those overexpressing F6H4 accumulated malonylglycoside forms of 6-hydroxydaidzein (M_6HD), and co-expression of F6H4 and IOMT3 increased the level of malonylglycitin but not of M_6HD. These results indicate that F6H4 and IOMT3 are responsible for glycitein biosynthesis in soybean seed hypocotyl.