Progress and prospectus in genetics and genomics of Phytophthora root and stem rot resistance in soybean (Glycine max L.).

Soybean is one of the largest sources of protein and oil in the world and is also considered a "super crop" due to several industrial advantages. However, enhanced acreage and adoption of monoculture practices rendered the crop vulnerable to several diseases. Phytophthora root and stem rot (PRSR) caused by Phytophthora sojae is one of the most prevalent diseases adversely affecting soybean production globally. Deployment of genetic resistance is the most sustainable approach for avoiding yield losses due to this disease. PRSR resistance is complex in nature and difficult to address by conventional breeding alone. Genetic mapping through a cost-effective sequencing platform facilitates identification of candidate genes and associated molecular markers for genetic improvement against PRSR. Furthermore, with the help of novel genomic approaches, identification and functional characterization of Rps (resistance to Phytophthora sojae) have also progressed in the recent past, and more than 30 Rps genes imparting complete resistance to different PRSR pathotypes have been reported. In addition, many genomic regions imparting partial resistance have also been identified. Furthermore, the adoption of emerging approaches like genome editing, genomic-assisted breeding, and genomic selection can assist in the functional characterization of novel genes and their rapid introgression for PRSR resistance. Hence, in the near future, soybean growers will likely witness an increase in production by adopting PRSR-resistant cultivars. This review highlights the progress made in deciphering the genetic architecture of PRSR resistance, genomic advances, and future perspectives for the deployment of PRSR resistance in soybean for the sustainable management of PRSR disease.

Modulation of GmFAD3 expression alters abiotic stress responses in soybean.

KEY MESSAGE: This study focused on enhancing resilience of soybean crops to drought and salinity stresses by overexpression of GmFAD3A gene, which plays an important role in modulating membrane fluidity and ultimately influence plants response to various abiotic stresses. Fatty acid desaturases (FADs) are a class of enzymes that mediate desaturation of fatty acids by introducing double bonds. They play an important role in modulating membrane fluidity in response to various abiotic stresses. However, a comprehensive analysis of GmFAD3 in drought and salinity stress tolerance in soybean is lacking. We used bean pod mottle virus (BPMV)-based vector for achieving rapid and efficient overexpression as well as silencing of Omega-3 Fatty Acid Desaturase gene from Glycine max (GmFAD3) to assess the functional role of GmFAD3 in abiotic stress responses in soybean. Higher levels of recombinant BPMV-GmFAD3A transcripts were detected in overexpressing soybean plants. Overexpression of GmFAD3A in soybean resulted in increased levels of jasmonic acid and higher expression of GmWRKY54 as compared to mock-inoculated, vector-infected and FAD3-silenced soybean plants under drought and salinity stress conditions. The GmFAD3A-overexpressing plants showed higher levels of chlorophyll content, efficient photosystem-II, relative water content, transpiration rate, stomatal conductance, proline content and also cooler canopy under drought and salinity stress conditions as compared to mock-inoculated, vector-infected and FAD3-silenced soybean plants. Results from the current study revealed that GmFAD3A-overexpressing soybean plants exhibited tolerance to drought and salinity stresses. However, soybean plants silenced for GmFAD3 were vulnerable to drought and salinity stresses.

Turning Waste into Beneficial Resource: Implication of Ageratum conyzoides L. in Sustainable Agriculture, Environment and Biopharma Sectors.

The annual herb, Ageratum conyzoides L. (Asteraceae), is distributed throughout the world. Although invasive, it can be very useful as a source of essential oils, pharmaceuticals, biopesticides, and bioenergy. However, very limited information exists on the molecular basis of its different utility as previous investigations were mainly focused on phytochemical/biological activity profiling. Here we have explored various properties of A. conyzoides that may offer environmental, ecological, agricultural, and health benefits. As this aromatic plant harbors many important secondary metabolites that may have various implications, biotechnological interventions such as genomics, metabolomics and tissue-culture can be indispensable tools for their mass-production. Further, A. conyzoides acts as a natural reservoir of begomoviruses affecting a wide range of plant species. As the mechanisms of disease spreading and crop infection are not fully clear, whole-genome sequencing and various advanced molecular technologies including RNAi, CRISPER/Cas9, multi-omics approaches, etc., may aid to decipher the molecular mechanism of such disease development and thus, can be useful in crop protection. Overall, improved knowledge of A. conyzoides is not only essential for developing sustainable weed control strategy but can also offer potential ways for biomedicinal, environment, safe and clean agriculture applications.

Breeding for higher yield, early maturity, wider adaptability and waterlogging tolerance in soybean (Glycine max L.): A case study.

Breeding for higher yield and wider adaptability are major objectives of soybean crop improvement. In the present study, 68 advanced breeding lines along with seven best checks were evaluated for yield and attributing traits by following group balanced block design. Three blocks were constituted based on the maturity duration of the breeding lines. High genetic variability for the twelve quantitative traits was found within and across the three blocks. Several genotypes were found to outperform check varieties for yield and attributing traits. During the same crop season, one of the promising entries, NRC 128,was evaluated across seven locations for its wider adaptability and it has shown stable performance in Northern plain Zone with > 20% higher yield superiority over best check PS 1347. However, it produced 9.8% yield superiority over best check in Eastern Zone. Screening for waterlogging tolerance under artificial conditions revealed that NRC 128 was on par with the tolerant variety JS 97-52. Based on the yield superiority, wider adaptability and waterlogging tolerance, NRC 128 was released and notified by Central Varietal Release Committee (CVRC) of India, for its cultivation across Eastern and Northern Plain Zones of India.

Probabilistically sampled and spectrally clustered plant species using phenotypic characteristics.

Phenotypic characteristics of a plant species refers to its physical properties as cataloged by plant biologists at different research centers around the world. Clustering species based upon their phenotypic characteristics is used to obtain diverse sets of parents that are useful in their breeding programs. The Hierarchical Clustering (HC) algorithm is the current standard in clustering of phenotypic data. This algorithm suffers from low accuracy and high computational complexity issues. To address the accuracy challenge, we propose the use of Spectral Clustering (SC) algorithm. To make the algorithm computationally cheap, we propose using sampling, specifically, Pivotal Sampling that is probability based. Since application of samplings to phenotypic data has not been explored much, for effective comparison, another sampling technique called Vector Quantization (VQ) is adapted for this data as well. VQ has recently generated promising results for genotypic data. The novelty of our SC with Pivotal Sampling algorithm is in constructing the crucial similarity matrix for the clustering algorithm and defining probabilities for the sampling technique. Although our algorithm can be applied to any plant species, we tested it on the phenotypic data obtained from about 2,400 Soybean species. SC with Pivotal Sampling achieves substantially more accuracy (in terms of Silhouette Values) than all the other proposed competitive clustering with sampling algorithms (i.e. SC with VQ, HC with Pivotal Sampling, and HC with VQ). The complexities of our SC with Pivotal Sampling algorithm and these three variants are almost the same because of the involved sampling. In addition to this, SC with Pivotal Sampling outperforms the standard HC algorithm in both accuracy and computational complexity. We experimentally show that we are up to 45% more accurate than HC in terms of clustering accuracy. The computational complexity of our algorithm is more than a magnitude less than that of HC.

Vector Quantized Spectral Clustering Applied to Whole Genome Sequences of Plants.

We develop a Vector Quantized Spectral Clustering (VQSC) algorithm that is a combination of spectral clustering (SC) and vector quantization (VQ) sampling for grouping genome sequences of plants. The inspiration here is to use SC for its accuracy and VQ to make the algorithm computationally cheap (the complexity of SC is cubic in terms of the input size). Although the combination of SC and VQ is not new, the novelty of our work is in developing the crucial similarity matrix in SC as well as use of k-medoids in VQ, both adapted for the plant genome data. For Soybean, we compare our approach with commonly used techniques like Un-weighted Pair Graph Method with Arithmetic mean (UPGMA) and Neighbor Joining (NJ). Experimental results show that our VQSC outperforms both these techniques significantly in terms of cluster quality (average improvement of 21% over UPGMA and 24% over NJ) as well as time complexity (order of magnitude faster than both UPGMA and NJ).

MultiSyn: A Webtool for Multiple Synteny Detection and Visualization of User's Sequence of Interest Compared to Public Plant Species.

Information on multiple synteny between plants and/or within a plant is key information to understand genome evolution. In addition, visualization of multiple synteny is helpful in interpreting evolution. So far, some web applications have been developed to determine and visualize multiple homology regions at once. However, the applications are not fully convenient for biologists because some of them do not include the function of synteny determination but visualize the multiple synteny plots by allowing users to upload their synteny data by determining the synteny based only on BLAST similarity information, with some algorithms not designed for synteny determination. Here, we introduce a web application that determines and visualizes multiple synteny from two types of files, simplified browser extensible data and protein sequence file by MCScanX algorithm, which have been used in many synteny studies.

QTLomics in Soybean: A Way Forward for Translational Genomics and Breeding.

Food legumes play an important role in attaining both food and nutritional security along with sustainable agricultural production for the well-being of humans globally. The various traits of economic importance in legume crops are complex and quantitative in nature, which are governed by quantitative trait loci (QTLs). Mapping of quantitative traits is a tedious and costly process, however, a large number of QTLs has been mapped in soybean for various traits albeit their utilization in breeding programmes is poorly reported. For their effective use in breeding programme it is imperative to narrow down the confidence interval of QTLs, to identify the underlying genes, and most importantly allelic characterization of these genes for identifying superior variants. In the field of functional genomics, especially in the identification and characterization of gene responsible for quantitative traits, soybean is far ahead from other legume crops. The availability of genic information about quantitative traits is more significant because it is easy and effective to identify homologs than identifying shared syntenic regions in other crop species. In soybean, genes underlying QTLs have been identified and functionally characterized for phosphorous efficiency, flowering and maturity, pod dehiscence, hard-seededness, α-Tocopherol content, soybean cyst nematode, sudden death syndrome, and salt tolerance. Candidate genes have also been identified for many other quantitative traits for which functional validation is required. Using the sequence information of identified genes from soybean, comparative genomic analysis of homologs in other legume crops could discover novel structural variants and useful alleles for functional marker development. The functional markers may be very useful for molecular breeding in soybean and harnessing benefit of translational research from soybean to other leguminous crops. Thus, soybean crop can act as a model crop for translational genomics and breeding of quantitative traits in legume crops. In this review, we summarize current status of identification and characterization of genes underlying QTLs for various quantitative traits in soybean and their significance in translational genomics and breeding of other legume crops.

Comparative and evolutionary analysis of major peanut allergen gene families.

Peanut (Arachis hypogaea L.) causes one of the most serious food allergies. Peanut seed proteins, Arah1, Arah2, and Arah3, are considered to be among the most important peanut allergens. To gain insights into genome organization and evolution of allergen-encoding genes, approximately 617 kb from the genome of cultivated peanut and 215 kb from a wild relative were sequenced including three Arah1, one Arah2, eight Arah3, and two Arah6 gene family members. To assign polarity to differences between homoeologous regions in peanut, we used as outgroups the single orthologous regions in Medicago, Lotus, common bean, chickpea, and pigeonpea, which diverged from peanut about 50 Ma and have not undergone subsequent polyploidy. These regions were also compared with orthologs in many additional dicot plant species to help clarify the timing of evolutionary events. The lack of conservation of allergenic epitopes between species, and the fact that many different proteins can be allergenic, makes the identification of allergens across species by comparative studies difficult. The peanut allergen genes are interspersed with low-copy genes and transposable elements. Phylogenetic analyses revealed lineage-specific expansion and loss of low-copy genes between species and homoeologs. Arah1 syntenic regions are conserved in soybean, pigeonpea, tomato, grape, Lotus, and Arabidopsis, whereas Arah3 syntenic regions show genome rearrangements. We infer that tandem and segmental duplications led to the establishment of the Arah3 gene family. Our analysis indicates differences in conserved motifs in allergen proteins and in the promoter regions of the allergen-encoding genes. Phylogenetic analysis and genomic organization studies provide new insights into the evolution of the major peanut allergen-encoding genes.

Plant miRNAome and antiviral resistance: a retrospective view and prospective challenges.

MicroRNAs (miRNAs) are small regulatory RNAs that play a defining role in post-transcriptional gene silencing of eukaryotes by either mRNA cleavage or translational inhibition. Plant miRNAs have been implicated in innumerable growth and developmental processes that extend beyond their ability to respond to biotic and abiotic stresses. Active in an organism's immune defence response, host miRNAs display a propensity to target viral genomes. During viral invasion, these virus-targeting miRNAs can be identified by their altered expression. All the while, pathogenic viruses, as a result of their long-term interaction with plants, have been evolving viral suppressors of RNA silencing (VSRs), as well as viral-encoded miRNAs as a counter-defence strategy. However, the gene silencing attribute of miRNAs has been ingeniously manipulated to down-regulate the expression of any gene of interest, including VSRs, in artificial miRNA (amiRNA)-based transgenics. Since we currently have a better understanding of the intricacies of miRNA-mediated gene regulation in plant-virus interactions, the majority of miRNAs manipulated to confer antiviral resistance to date are in plants. This review will share the insights gained from the studies of plant-virus combat and from the endeavour to manipulate miRNAs, including prospective challenges in the context of the evolutionary dynamics of the viral genome. Next generation sequencing technologies and bioinformatics analysis will further delineate the molecular details of host-virus interactions. The need for appropriate environmental risk assessment principles specific to amiRNA-based virus resistance is also discussed.

The repetitive component of the A genome of peanut (Arachis hypogaea) and its role in remodelling intergenic sequence space since its evolutionary divergence from the B genome.

BACKGROUND AND AIMS: Peanut (Arachis hypogaea) is an allotetraploid (AABB-type genome) of recent origin, with a genome of about 2·8 Gb and a high repetitive content. This study reports an analysis of the repetitive component of the peanut A genome using bacterial artificial chromosome (BAC) clones from A. duranensis, the most probable A genome donor, and the probable consequences of the activity of these elements since the divergence of the peanut A and B genomes. METHODS: The repetitive content of the A genome was analysed by using A. duranensis BAC clones as probes for fluorescence in situ hybridization (BAC-FISH), and by sequencing and characterization of 12 genomic regions. For the analysis of the evolutionary dynamics, two A genome regions are compared with their B genome homeologues. KEY RESULTS: BAC-FISH using 27 A. duranensis BAC clones as probes gave dispersed and repetitive DNA characteristic signals, predominantly in interstitial regions of the peanut A chromosomes. The sequences of 14 BAC clones showed complete and truncated copies of ten abundant long terminal repeat (LTR) retrotransposons, characterized here. Almost all dateable transposition events occurred <3·5 million years ago, the estimated date of the divergence of A and B genomes. The most abundant retrotransposon is Feral, apparently parasitic on the retrotransposon FIDEL, followed by Pipa, also non-autonomous and probably parasitic on a retrotransposon we named Pipoka. The comparison of the A and B genome homeologous regions showed conserved segments of high sequence identity, punctuated by predominantly indel regions without significant similarity. CONCLUSIONS: A substantial proportion of the highly repetitive component of the peanut A genome appears to be accounted for by relatively few LTR retrotransposons and their truncated copies or solo LTRs. The most abundant of the retrotransposons are non-autonomous. The activity of these retrotransposons has been a very significant driver of genome evolution since the evolutionary divergence of the A and B genomes.

Evolution of a complex disease resistance gene cluster in diploid Phaseolus and tetraploid Glycine.

We used a comparative genomics approach to investigate the evolution of a complex nucleotide-binding (NB)-leucine-rich repeat (LRR) gene cluster found in soybean (Glycine max) and common bean (Phaseolus vulgaris) that is associated with several disease resistance (R) genes of known function, including Rpg1b (for Resistance to Pseudomonas glycinea1b), an R gene effective against specific races of bacterial blight. Analysis of domains revealed that the amino-terminal coiled-coil (CC) domain, central nucleotide-binding domain (NB-ARC [for APAF1, Resistance genes, and CED4]), and carboxyl-terminal LRR domain have undergone distinct evolutionary paths. Sequence exchanges within the NB-ARC domain were rare. In contrast, interparalogue exchanges involving the CC and LRR domains were common, consistent with both of these regions coevolving with pathogens. Residues under positive selection were overrepresented within the predicted solvent-exposed face of the LRR domain, although several also were detected within the CC and NB-ARC domains. Superimposition of these latter residues onto predicted tertiary structures revealed that the majority are located on the surface, suggestive of a role in interactions with other domains or proteins. Following polyploidy in the Glycine lineage, NB-LRR genes have been preferentially lost from one of the duplicated chromosomes (homeologues found in soybean), and there has been partitioning of NB-LRR clades between the two homeologues. The single orthologous region in common bean contains approximately the same number of paralogues as found in the two soybean homeologues combined. We conclude that while polyploidization in Glycine has not driven a stable increase in family size for NB-LRR genes, it has generated two recombinationally isolated clusters, one of which appears to be in the process of decay.

Comparative analysis of peanut NBS-LRR gene clusters suggests evolutionary innovation among duplicated domains and erosion of gene microsynteny.

• Plant genomes contain numerous disease resistance genes (R genes) that play roles in defense against pathogens. Scarcity of genetic polymorphism makes peanut (Arachis hypogaea) especially vulnerable to a wide variety of pathogens. • Here, we isolated and characterized peanut bacterial artificial chromosomes (BACs) containing a high density of R genes. Analysis of two genomic regions identified several TIR-NBS-LRR (Toll-interleukin-1 receptor, nucleotide-binding site, leucine-rich repeat) resistance gene analogs or gene fragments. We reconstructed their evolutionary history characterized by tandem duplications, possibly facilitated by transposon activities. We found evidence of both intergenic and intragenic gene conversions and unequal crossing-over, which may be driving forces underlying the functional evolution of resistance. • Analysis of the sequence mutations, protein secondary structure and three-dimensional structures, all suggest that LRR domains are the primary contributor to the evolution of resistance genes. The central part of LRR regions, assumed to serve as the active core, may play a key role in the resistance function by having higher rates of duplication and DNA conversion than neighboring regions. The assumed active core is characterized by significantly enriched leucine residue composition, accumulation of positively selected sites, and shorter beta sheets. • Homologous resistance gene analog (RGA)-containing regions in peanut, soybean, Medicago, Arabidopsis and grape have only limited gene synteny and microcollinearity.

Replication of nonautonomous retroelements in soybean appears to be both recent and common.

Retrotransposons and their remnants often constitute more than 50% of higher plant genomes. Although extensively studied in monocot crops such as maize (Zea mays) and rice (Oryza sativa), the impact of retrotransposons on dicot crop genomes is not well documented. Here, we present an analysis of retrotransposons in soybean (Glycine max). Analysis of approximately 3.7 megabases (Mb) of genomic sequence, including 0.87 Mb of pericentromeric sequence, uncovered 45 intact long terminal repeat (LTR)-retrotransposons. The ratio of intact elements to solo LTRs was 8:1, one of the highest reported to date in plants, suggesting that removal of retrotransposons by homologous recombination between LTRs is occurring more slowly in soybean than in previously characterized plant species. Analysis of paired LTR sequences uncovered a low frequency of deletions relative to base substitutions, indicating that removal of retrotransposon sequences by illegitimate recombination is also operating more slowly. Significantly, we identified three subfamilies of nonautonomous elements that have replicated in the recent past, suggesting that retrotransposition can be catalyzed in trans by autonomous elements elsewhere in the genome. Analysis of 1.6 Mb of sequence from Glycine tomentella, a wild perennial relative of soybean, uncovered 23 intact retroelements, two of which had accumulated no mutations in their LTRs, indicating very recent insertion. A similar pattern was found in 0.94 Mb of sequence from Phaseolus vulgaris (common bean). Thus, autonomous and nonautonomous retrotransposons appear to be both abundant and active in Glycine and Phaseolus. The impact of nonautonomous retrotransposon replication on genome size appears to be much greater than previously appreciated.

Differential accumulation of retroelements and diversification of NB-LRR disease resistance genes in duplicated regions following polyploidy in the ancestor of soybean.

The genomes of most, if not all, flowering plants have undergone whole genome duplication events during their evolution. The impact of such polyploidy events is poorly understood, as is the fate of most duplicated genes. We sequenced an approximately 1 million-bp region in soybean (Glycine max) centered on the Rpg1-b disease resistance gene and compared this region with a region duplicated 10 to 14 million years ago. These two regions were also compared with homologous regions in several related legume species (a second soybean genotype, Glycine tomentella, Phaseolus vulgaris, and Medicago truncatula), which enabled us to determine how each of the duplicated regions (homoeologues) in soybean has changed following polyploidy. The biggest change was in retroelement content, with homoeologue 2 having expanded to 3-fold the size of homoeologue 1. Despite this accumulation of retroelements, over 77% of the duplicated low-copy genes have been retained in the same order and appear to be functional. This finding contrasts with recent analyses of the maize (Zea mays) genome, in which only about one-third of duplicated genes appear to have been retained over a similar time period. Fluorescent in situ hybridization revealed that the homoeologue 2 region is located very near a centromere. Thus, pericentromeric localization, per se, does not result in a high rate of gene inactivation, despite greatly accelerated retrotransposon accumulation. In contrast to low-copy genes, nucleotide-binding-leucine-rich repeat disease resistance gene clusters have undergone dramatic species/homoeologue-specific duplications and losses, with some evidence for partitioning of subfamilies between homoeologues.