Rpp1 Encodes a ULP1-NBS-LRR Protein That Controls Immunity to Phakopsora pachyrhizi in Soybean

BjuA03.BNT1 plays a positive role in resistance to clubroot disease in resynthesized Brassica juncea L

Clubroot has become a major obstacle in rapeseed production. Breeding varieties resistant to clubroot is the most effective method for disease management. However, the clubroot-resistant germplasm of rapeseed remains limited. To tackle this challenge, we synthesized the clubroot-resistant mustard, CT19, via distant hybridization, and subsequently an F2 segregating population was created by intercrossing CT19 with a clubroot-susceptible germplasm CS15. A major-effect clubroot resistance QTL qCRa3-1 on chromosome A03 was identified through QTL scanning. Transcriptome analyses of CT19 and CS15 revealed that the mechanisms conferring resistance to Plasmodiophora brassica likely involved the regulation of flavonoid metabolism, fatty acid metabolism, and sulfur metabolism. By combining the results from transcriptome, QTL mapping, and gene sequencing, a candidate gene BjuA03.BNT1, encoding NLR (nucleotide-binding domain leucine-rich repeat-containing receptors) protein, was obtained. Intriguingly, comparing with CT19, a base T insertion was discovered in the BjuA03.BNT1 gene's coding sequence in CS15, resulting an alteration within the LRR conserved domain. Overexpression of BjuA03.BNT1 from CT19 notably enhanced the resistance to clubroot in Arabidopsis. Our investigations revealed that BjuA03.BNT1 regulated the resistance to clubroot by modulating fatty acid synthesis and the structure of cell wall. These results are highly relevant for molecular breeding to improve clubroot resistance in rapeseed.

Allelic variability in the Rpp1 locus conferring resistance to Asian soybean rust revealed by genome-wide association

Soybean is a crucial crop for the Brazilian economy, but it faces challenges from the biotrophic fungus Phakopsora pachyrhizi, which causes Asian Soybean Rust (ASR). In this study, we aimed to identify SNPs associated with resistance within the Rpp1 locus, which is effective against Brazilian ASR populations. We employed GWAS and re-sequencing analyzes to pinpoint SNP markers capable of differentiating between soybean accessions harboring the Rpp1, Rpp1-b and other alternative alleles in the Rpp1 locus and from susceptible soybean cultivars. Seven SNP markers were found to be associated with ASR resistance through GWAS, with three of them defining haplotypes that efficiently distinguished the accessions based on their ASR resistance and source of the Rpp gene. These haplotypes were subsequently validated using a bi-parental population and a diverse set of Rpp sources, demonstrating that the GWAS markers co-segregate with ASR resistance. We then examined the presence of these haplotypes in a diverse set of soybean genomes worldwide, finding a few new potential sources of Rpp1/Rpp1-b. Further genomic sequence analysis revealed nucleotide differences within the genes present in the Rpp1 locus, including the ULP1-NBS-LRR genes, which are potential R gene candidates. These results provide valuable insights into ASR resistance in soybean, thus helping the development of resistant soybean varieties through genetic breeding programs.

The role of microRNAs in NBS-LRR gene expression and its implications for plant immunity and crop development

Plants evolved, over millions of years, complex defense systems against pathogens. Once infected, the interaction between pathogen effector molecules and host receptors triggers plant immune responses, which include apoptosis, systemic immune response, among others. An important protein family responsible for pathogen effector recognition is the nucleotide binding site-leucine repeat rich (NBS-LRR) proteins. The NBS-LRR gene family is the largest disease resistance gene class in plants. These proteins are widely distributed in vascular plants and have a complex multigenic cluster distribution in plant genomes. To counteract the genetic load of such a large gene family on fitness cost, plants evolved a mechanism using post transcriptional gene silencing induced by small RNAs, particularly microRNAs. For the NBS-LRR gene family, the small RNAs involved in this silencing mechanism are mainly the microRNA482/2118 superfamily. This suppression mechanism is relieved upon pathogen infection, thus allowing increased NBS-LRR expression and triggering plant immunity. In this review, we will discuss the biogenesis of microRNAs and secondary RNAs involved in this silencing mechanism, biochemical and structural features of NBS-LRR proteins in response to pathogen effectors and the evolution of microRNA-based silencing mechanism with a focus on the miR482/2118 family. Furthermore, the biotechnological manipulation of microRNA expression, using both transgenic or genome editing approaches to improve cultivated plants will be discussed, with a focus on the miR482/2118 family in soybean.

The Soybean Rpp3 Gene Encodes a TIR-NBS-LRR Protein that Confers Resistance to Phakopsora pachyrhizi

Soybean rust is an economically significant disease caused by the fungus Phakopsora pachyrhizi that negatively impacts soybean (Glycine max [L.] Merr.) production throughout the world. Susceptible plants infected by P. pachyrhizi develop tan-colored lesions on the leaf surface that give rise to funnel-shaped uredinia as the disease progresses. While most soybean germplasm is susceptible, seven genetic loci (Rpp1 to Rpp7) that provide race-specific resistance to P. pachyrhizi (Rpp) have been identified. Rpp3 was first discovered and characterized in the soybean accession PI 462312 (Ankur), and it was also determined to be one of two Rpp genes present in PI 506764 (Hyuuga). Genetic crosses with PI 506764 were later used to fine-map the Rpp3 locus to a 371-kb region on chromosome 6. The corresponding region in the susceptible Williams 82 (Wm82) reference genome contains several homologous nucleotide binding site-leucine rich repeat (NBS-LRR) genes. To identify Rpp3, we designed oligonucleotide primers to amplify Rpp3 candidate (Rpp3C) NBS-LRR genes at this locus from PI 462312, PI 506764, and Wm82 using polymerase chain reaction (PCR). Five Rpp3C genes were identified in both Rpp3-resistant soybean lines, and co-silencing these genes compromised resistance to P. pachyrhizi. Gene expression analysis and sequence comparisons of the Rpp3C genes in PI 462312 and PI 506764 suggest that a single candidate gene, Rpp3C3, is responsible for Rpp3-mediated resistance. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

An pair of an atypical NLR encoding genes confer Asian soybean rust resistance in soybean

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is a devastating disease that is present in all major soybean-producing regions. The limited availability of resistant germplasm has resulted in a scarcity of commercial soybean cultivars that are resistant to the disease. To date, only the Chinese soybean landrace SX6907 has demonstrated an immune response to ASR. In this study, we present the isolation and characterization of Rpp6907-7 and Rpp6907-4, a gene pair that confer broad-spectrum resistance to ASR. Rpp6907-7 and Rpp6907-4 encode atypic nucleotide-binding leucine-rich repeat (NLR) proteins that are found to be required for NLR-mediated immunity. Genetic analysis shows that only Rpp6907-7 confers resistance, while Rpp6907-4 regulates Rpp6907-7 signaling activity by acting as a repressor in the absence of recognized effectors. Our work highlights the potential value of using Rpp6907 in developing resistant soybean cultivars.

GmGLU1 and GmRR4 contribute to iron deficiency tolerance in soybean

Iron deficiency chlorosis (IDC) is a form of abiotic stress that negatively impacts soybean yield. In a previous study, we demonstrated that the historical IDC quantitative trait locus (QTL) on soybean chromosome Gm03 was composed of four distinct linkage blocks, each containing candidate genes for IDC tolerance. Here, we take advantage of virus-induced gene silencing (VIGS) to validate the function of three high-priority candidate genes, each corresponding to a different linkage block in the Gm03 IDC QTL. We built three single-gene constructs to target GmGLU1 (GLUTAMATE SYNTHASE 1, Glyma.03G128300), GmRR4 (RESPONSE REGULATOR 4, Glyma.03G130000), and GmbHLH38 (beta Helix Loop Helix 38, Glyma.03G130400 and Glyma.03G130600). Given the polygenic nature of the iron stress tolerance trait, we also silenced the genes in combination. We built two constructs targeting GmRR4+GmGLU1 and GmbHLH38+GmGLU1. All constructs were tested on the iron-efficient soybean genotype Clark grown in iron-sufficient conditions. We observed significant decreases in soil plant analysis development (SPAD) measurements using the GmGLU1 construct and both double constructs, with potential additive effects in the GmRR4+GmGLU1 construct. Whole genome expression analyses (RNA-seq) revealed a wide range of affected processes including known iron stress responses, defense and hormone signaling, photosynthesis, and cell wall structure. These findings highlight the importance of GmGLU1 in soybean iron stress responses and provide evidence that IDC is truly a polygenic trait, with multiple genes within the QTL contributing to IDC tolerance. Finally, we conducted BLAST analyses to demonstrate that the Gm03 IDC QTL is syntenic across a broad range of plant species.

Soybean-Phakopsora pachyrhizi interactions: towards the development of next-generation disease-resistant plants

Soybean rust (SBR), caused by the obligate biotrophic fungus Phakopsora pachyrhizi, is a devastating foliar disease threatening soybean production. To date, no commercial cultivars conferring durable resistance to SBR are available. The development of long-lasting SBR resistance has been hindered by the lack of understanding of this complex pathosystem, encompassing challenges posed by intricate genetic structures in both the host and pathogen, leading to a gap in the knowledge of gene-for-gene interactions between soybean and P. pachyrhizi. In this review, we focus on recent advancements and emerging technologies that can be used to improve our understanding of the P. pachyrhizi-soybean molecular interactions. We further explore approaches used to combat SBR, including conventional breeding, transgenic approaches and RNA interference, and how advances in our understanding of plant immune networks, the availability of new molecular tools, and the recent sequencing of the P. pachyrhizi genome could be used to aid in the development of better genetic resistance against SBR. Lastly, we discuss the research gaps of this pathosystem and how new technologies can be used to shed light on these questions and to develop durable next-generation SBR-resistant soybean plants.

Virus induced gene silencing confirms oligogenic inheritance of brown stem rot resistance in soybean

Brown Stem Rot (BSR), caused by the soil borne fungal pathogen Phialophora gregata, can reduce soybean yields by as much as 38%. Previous allelism studies identified three Resistant to brown stem Rot genes (Rbs1, Rbs2, and Rbs3), all mapping to large, overlapping regions on soybean chromosome 16. However, recent fine-mapping and genome wide association studies (GWAS) suggest Rbs1, Rbs2, and Rbs3 are alleles of a single Rbs locus. To address this conflict, we characterized the Rbs locus using the Williams82 reference genome (Wm82.a4.v1). We identified 120 Receptor-Like Proteins (RLPs), with hallmarks of disease resistance receptor-like proteins (RLPs), which formed five distinct clusters. We developed virus induced gene silencing (VIGS) constructs to target each of the clusters, hypothesizing that silencing the correct RLP cluster would result in a loss of resistance phenotype. The VIGS constructs were tested against P. gregata resistant genotypes L78-4094 (Rbs1), PI 437833 (Rbs2), or PI 437970 (Rbs3), infected with P. gregata or mock infected. No loss of resistance phenotype was observed. We then developed VIGS constructs targeting two RLP clusters with a single construct. Construct B1a/B2 silenced P. gregata resistance in L78-4094, confirming at least two genes confer Rbs1-mediated resistance to P. gregata. Failure of B1a/B2 to silence resistance in PI 437833 and PI 437970 suggests additional genes confer BSR resistance in these lines. To identify differentially expressed genes (DEGs) responding to silencing, we conducted RNA-seq of leaf, stem and root samples from B1a/B2 and empty vector control plants infected with P. gregata or mock infected. B1a/B2 silencing induced DEGs associated with cell wall biogenesis, lipid oxidation, the unfolded protein response and iron homeostasis and repressed numerous DEGs involved in defense and defense signaling. These findings will improve integration of Rbs resistance into elite germplasm and provide novel insights into fungal disease resistance.

Comparative analysis of soybean transcriptional profiles reveals defense mechanisms involved in resistance against Diaporthe caulivora

Soybean stem canker (SSC) caused by the fungal pathogen Diaporthe caulivora is an important disease affecting soybean production worldwide. However, limited information related to the molecular mechanisms underlying soybean resistance to Diaporthe species is available. In the present work, we analyzed the defense responses to D. caulivora in the soybean genotypes Williams and Génesis 5601. The results showed that compared to Williams, Génesis 5601 is more resistant to fungal infection evidenced by significantly smaller lesion length, reduced disease severity and pathogen biomass. Transcriptional profiling was performed in untreated plants and in D. caulivora-inoculated and control-treated tissues at 8 and 48 h post inoculation (hpi). In total, 2.322 and 1.855 genes were differentially expressed in Génesis 5601 and Williams, respectively. Interestingly, Génesis 5601 exhibited a significantly higher number of upregulated genes compared to Williams at 8 hpi, 1.028 versus 434 genes. Resistance to D. caulivora was associated with defense activation through transcriptional reprogramming mediating perception of the pathogen by receptors, biosynthesis of phenylpropanoids, hormone signaling, small heat shock proteins and pathogenesis related (PR) genes. These findings provide novel insights into soybean defense mechanisms leading to host resistance against D. caulivora, and generate a foundation for the development of resistant SSC varieties within soybean breeding programs.

Plant immunity in soybean: progress, strategies, and perspectives

Soybean (Glycine max) is one of the most important commercial crops worldwide. Soybean hosts diverse microbes, including pathogens that may cause diseases and symbionts that contribute to nitrogen fixation. Study on soybean-microbe interactions to understand pathogenesis, immunity, and symbiosis represents an important research direction toward plant protection in soybean. In terms of immune mechanisms, current research in soybean lags far behind that in the model plants Arabidopsis and rice. In this review, we summarized the shared and unique mechanisms involved in the two-tiered plant immunity and the virulence function of pathogen effectors between soybean and Arabidopsis, providing a molecular roadmap for future research on soybean immunity. We also discussed disease resistance engineering and future perspectives in soybean.

An NBS-LRR protein in the Rpp1 locus negates the dominance of Rpp1-mediated resistance against Phakopsora pachyrhizi in soybean

The soybean Rpp1 locus confers resistance to Phakopsora pachyrhizi, causal agent of rust, and resistance is usually dominant over susceptibility. However, dominance of Rpp1-mediated resistance is lost when a resistant genotype (Rpp1 or Rpp1b) is crossed with susceptible line TMG06_0011, and the mechanism of this dominant susceptibility (DS) is unknown. Sequencing the Rpp1 region reveals that the TMG06_0011 Rpp1 locus has a single nucleotide-binding site leucine-rich repeat (NBS-LRR) gene (DS-R), whereas resistant PI 594760B (Rpp1b) is similar to PI 200492 (Rpp1) and has three NBS-LRR resistance gene candidates. Evidence that DS-R is the cause of DS was reflected in virus-induced gene silencing of DS-R in Rpp1b/DS-R or Rpp1/DS-R heterozygous plants with resistance partially restored. In heterozygous Rpp1b/DS-R plants, expression of Rpp1b candidate genes was not significantly altered, indicating no effect of DS-R on transcription. Physical interaction of the DS-R protein with candidate Rpp1b resistance proteins was supported by yeast two-hybrid studies and in silico modeling. Thus, we conclude that suppression of resistance most likely does not occur at the transcript level, but instead probably at the protein level, possibly with Rpp1 function inhibited by binding to the DS-R protein. The DS-R gene was found in other soybean lines, with an estimated allele frequency of 6% in a diverse population, and also found in wild soybean (Glycine soja). The identification of a dominant susceptible NBS-LRR gene provides insight into the behavior of NBS-LRR proteins and serves as a reminder to breeders that the dominance of an R gene can be influenced by a susceptibility allele.

N. Lopes I, Abdelnoor RV, Marcelino-Guimarães FC. Mapping of a soybean rust resistance in PI 594756 at the Rpp1 locus

Asian soybean rust (ASR), caused by the fungus Phakopsora pachyrhizi, is the main disease affecting soybean in Brazil. This study aimed at investigating and mapping the resistance of the PI 594756 to P. pachyrhizi, by using Bulked Segregant Analysis (BSA). The PI 594756 and the susceptible PI 594891 were crossed and the resulting F2 and F2:3 populations (208 and 1770 plants, respectively) were tested against ASR. Also, these PIs and differential varieties were tested against a panel of monosporic isolates. Plants presenting tan lesions were classified as susceptible (S) while plants presenting reddish-brown (RB) lesions were classified as resistant. DNA bulks were genotyped with Infinium BeadChips and the genomic region identified was further analyzed in the F2 individuals with target GBS (tGBS). PI 594,56 presented a unique resistance profile compared to the differential varieties. The resistance was monogenic dominant; however, it was classified as incompletely dominant when quantitatively studied. Genetic and QTL mapping placed the PI 594756 gene between the genomic region located at 55,863,741 and 56,123,516 bp of chromosome 18. This position is slightly upstream mapping positions of Rpp1 (PI 200492) and Rpp1-b (PI 594538A). Finally, we performed a haplotype analysis in a whole genomic sequencing-SNP database composed of Brazilian historical germplasm and sources of Rpp genes. We found SNPs that successfully differentiated the new PI 594756 allele from Rpp1 and Rpp1-b sources. The haplotype identified can be used as a tool for marker-assisted selection (MAS).

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01358-4.

Mapping QTLs Controlling Soybean Rust Disease Resistance in Chiang Mai 5, an Induced Mutant Cultivar

Soybean rust (SBR) caused by the fungus Phakopsora pachyrhizi is an important folia disease of soybean (Glycine max). In this study, we identified QTLs controlling SBR in Chiang Mai 5 (CM5), an SBR-resistant cultivar developed by induced mutation breeding. A recombinant inbred line (RIL) population of 108 lines developed from a cross between Sukhothai 2 (SKT2, a susceptible cultivar) and CM5 was evaluated for SBR resistance under field conditions in Thailand. QTL analysis for the resistance in the RIL population identified a single QTL, qSBR18.1, for resistance. qSBR18.1 was mapped to a 212-kb region on chromosome 18 between simple sequence repeat markers Satt288 and sc21_3420 and accounted for 21.31-35.09% depending on the traits evaluated for resistance. The qSBR18.1 interval overlapped with genomic regions containing resistance to P. pachyrhizi 4 (Rpp4), a locus for SBR resistance. Three tightly linked genes, Glyma.18G226250, Glyma.18G226300, and Glyma.18G226500, each encoding leucine-rich repeat-containing protein, were identified as candidate genes for SBR resistance at the qSRB18.1. The qSBR18.1 would be useful for breeding of SBR resistance.

Show me your ID: NLR immune receptors with integrated domains in plants

Nucleotide-binding and leucine-rich repeat receptors (NLRs) are intracellular plant immune receptors that recognize pathogen effectors secreted into the plant cell. Canonical NLRs typically contain three conserved domains including a central nucleotide binding (NB-ARC) domain, C-terminal leucine-rich repeats (LRRs) and an N-terminal domain. A subfamily of plant NLRs contain additional noncanonical domain(s) that have potentially evolved from the integration of the effector targets in the canonical NLR structure. These NLRs with extra domains are thus referred to as NLRs with integrated domains (NLR-IDs). Here, we first summarize our current understanding of NLR-ID activation upon effector binding, focusing on the NLR pairs Pik-1/Pik-2, RGA4/RGA5, and RRS1/RPS4. We speculate on their potential oligomerization into resistosomes as it was recently shown for certain canonical plant NLRs. Furthermore, we discuss how our growing understanding of the mode of action of NLR-ID continuously informs engineering approaches to design new resistance specificities in the context of rapidly evolving pathogens.

An alternative splicing isoform of wheat TaYRG1 resistance protein activates immunity by interacting with dynamin-related proteins

Wheat (Triticum aestivum) is a commercially important crop and its production is seriously threatened by the fungal pathogen Puccinia striiformis f. sp. tritici West (Pst). Resistance (R) genes are critical factors that facilitate plant immune responses. Here, we report a wheat R gene NB-ARC-LRR ortholog, TaYRG1, that is associated with distinct alternative splicing events in wheat infected by Pst. The native splice variant, TaYRG1.6, encodes internal-motif-deleted polypeptides with the same N- and C-termini as TaYRG1.1, resulting in gain of function. Transient expression of protein variants in Nicotiana benthamiana showed that the NB and ARC domains, and TaYRG1.6 (half LRR domain), stimulate robust elicitor-independent cell death based on a signal peptide, although the activity was negatively modulated by the CC and complete LRR domains. Furthermore, molecular genetic analyses indicated that TaYRG1.6 enhanced resistance to Pst in wheat. Moreover, we provide multiple lines of evidence that TaYRG1.6 interacts with a dynamin-related protein, TaDrp1. Proteome profiling suggested that the TaYRG1.6-TaDrp1-DNM complex in the membrane trafficking systems may trigger cell death by mobilizing lipid and kinase signaling in the endocytosis pathway. Our findings reveal a unique mechanism by which TaYRG1 activates cell death and enhances disease resistance by reconfiguring protein structure through alternative splicing.

Genome-based high-resolution mapping of fusarium wilt resistance in sweet basil

Fusarium wilt of basil is a disease of sweet basil (Ocimum basilicum L.) plants caused by the fungus Fusarium oxysporum f. sp. basilici (FOB). Although resistant cultivars were released > 20 years ago, the underlying mechanism and the genes controlling the resistance remain unknown. We used genetic mapping to elucidate FOB resistance in an F₂ population derived from a cross between resistant and susceptible cultivars. We performed genotyping by sequencing of 173 offspring and aligning the data to the sweet basil reference genome. In total, 23,411 polymorphic sites were detected, and a single quantitative trait locus (QTL) for FOB resistance was found. The confidence interval was < 600 kbp, harboring only 60 genes, including a cluster of putative disease-resistance genes. Based on homology to a fusarium resistance protein from wild tomato, we also investigated a candidate resistance gene that encodes a transmembrane leucine-rich repeat - receptor-like kinase - ubiquitin-like protease (LRR-RLK-ULP). Sequence analysis of that gene in the susceptible parent vs. the resistant parent revealed multiple indels, including an insertion of 20 amino acids next to the transmembrane domain, which might alter its functionality. Our findings suggest that this LRR-RLK-ULP might be responsible for FOB resistance in sweet basil and demonstrate the usefulness of the recently sequenced basil genome for QTL mapping and gene mining.

Molecular Breeding to Overcome Biotic Stresses in Soybean: Update

Soybean (Glycine max (L.) Merr.) is an important leguminous crop and biotic stresses are a global concern for soybean growers. In recent decades, significant development has been carried outtowards identification of the diseases caused by pathogens, sources of resistance and determination of loci conferring resistance to different diseases on linkage maps of soybean. Host-plant resistance is generally accepted as the bestsolution because of its role in the management of environmental and economic conditions of farmers owing to low input in terms of chemicals. The main objectives of soybean crop improvement are based on the identification of sources of resistance or tolerance against various biotic as well as abiotic stresses and utilization of these sources for further hybridization and transgenic processes for development of new cultivars for stress management. The focus of the present review is to summarize genetic aspects of various diseases caused by pathogens in soybean and molecular breeding research work conducted to date.

Progress in soybean functional genomics over the past decade

Soybean is one of the most important oilseed and fodder crops. Benefiting from the efforts of soybean breeders and the development of breeding technology, large number of germplasm has been generated over the last 100 years. Nevertheless, soybean breeding needs to be accelerated to meet the needs of a growing world population, to promote sustainable agriculture and to address future environmental changes. The acceleration is highly reliant on the discoveries in gene functional studies. The release of the reference soybean genome in 2010 has significantly facilitated the advance in soybean functional genomics. Here, we review the research progress in soybean omics (genomics, transcriptomics, epigenomics and proteomics), germplasm development (germplasm resources and databases), gene discovery (genes that are responsible for important soybean traits including yield, flowering and maturity, seed quality, stress resistance, nodulation and domestication) and transformation technology during the past decade. At the end, we also briefly discuss current challenges and future directions.

Mining Fiskeby III and Mandarin (Ottawa) Expression Profiles to Understand Iron Stress Tolerant Responses in Soybean

The soybean (Glycine max L. merr) genotype Fiskeby III is highly resistant to a multitude of abiotic stresses, including iron deficiency, incurring only mild yield loss during stress conditions. Conversely, Mandarin (Ottawa) is highly susceptible to disease and suffers severe phenotypic damage and yield loss when exposed to abiotic stresses such as iron deficiency, a major challenge to soybean production in the northern Midwestern United States. Using RNA-seq, we characterize the transcriptional response to iron deficiency in both Fiskeby III and Mandarin (Ottawa) to better understand abiotic stress tolerance. Previous work by our group identified a quantitative trait locus (QTL) on chromosome 5 associated with Fiskeby III iron efficiency, indicating Fiskeby III utilizes iron deficiency stress mechanisms not previously characterized in soybean. We targeted 10 of the potential candidate genes in the Williams 82 genome sequence associated with the QTL using virus-induced gene silencing. Coupling virus-induced gene silencing with RNA-seq, we identified a single high priority candidate gene with a significant impact on iron deficiency response pathways. Characterization of the Fiskeby III responses to iron stress and the genes underlying the chromosome 5 QTL provides novel targets for improved abiotic stress tolerance in soybean.

Mitogen activated protein kinase (MAPK)-regulated genes with predicted signal peptides function in the Glycine max defense response to the root pathogenic nematode Heterodera glycines

Glycine max has 32 mitogen activated protein kinases (MAPKs), nine of them exhibiting defense functions (defense MAPKs) to the plant parasitic nematode Heterodera glycines. RNA seq analyses of transgenic G. max lines overexpressing (OE) each defense MAPK has led to the identification of 309 genes that are increased in their relative transcript abundance by all 9 defense MAPKs. Here, 71 of those genes are shown to also have measurable amounts of transcript in H. glycines-induced nurse cells (syncytia) produced in the root that are undergoing a defense response. The 71 genes have been grouped into 7 types, based on their expression profile. Among the 71 genes are 8 putatively-secreted proteins that include a galactose mutarotase-like protein, pollen Ole e 1 allergen and extensin protein, endomembrane protein 70 protein, O-glycosyl hydrolase 17 protein, glycosyl hydrolase 32 protein, FASCICLIN-like arabinogalactan protein 17 precursor, secreted peroxidase and a pathogenesis-related thaumatin protein. Functional transgenic analyses of all 8 of these candidate defense genes that employ their overexpression and RNA interference (RNAi) demonstrate they have a role in defense. Overexpression experiments that increase the relative transcript abundance of the candidate defense gene reduces the ability that the plant parasitic nematode Heterodera glycines has in completing its life cycle while, in contrast, RNAi of these genes leads to an increase in parasitism. The results provide a genomic analysis of the importance of MAPK signaling in relation to the secretion apparatus during the defense process defense in the G. max-H. glycines pathosystem and identify additional targets for future studies.

Whole Genome Re-sequencing of Soybean Accession EC241780 Providing Genomic Landscape of Candidate Genes Involved in Rust Resistance

BACKGROUND

In this study, whole genome re-sequencing of rust resistant soybean genotype EC241780 was performed to understand the genomic landscape involved in the resistance mechanism.

METHODS

A total of 374 million raw reads were obtained with paired-end sequencing performed with Illumina HiSeq 2500 instrument, out of which 287.3 million high quality reads were mapped to Williams 82 reference genome. Comparative sequence analysis of EC241780 with rust susceptible cultivars Williams 82 and JS 335 was performed to identify sequence variation and to prioritise the candidate genes.

RESULTS

Comparative analysis indicates that genotype EC241780 has high sequence similarity with rust resistant genotype PI 200492 and the resistance in EC241780 is conferred by the Rpp1 locus. Based on the sequence variations and functional annotations, three genes Glyma18G51715, Glyma18G51741 and Glyma18G51765 encoding for NBS-LRR family protein were identified as the most prominent candidate for Rpp1 locus.

CONCLUSION

The study provides insights of genome-wide sequence variation more particularly at Rpp1 loci which will help to develop rust resistant soybean cultivars through efficient exploration of the genomic resource.