Development and Genetic Characterization of Peanut Advanced Backcross Lines That Incorporate Root-Knot Nematode Resistance From Arachis stenosperma

Crop wild species are increasingly important for crop improvement. Peanut (Arachis hypogaea L.) wild relatives comprise a diverse genetic pool that is being used to broaden its narrow genetic base. Peanut is an allotetraploid species extremely susceptible to peanut root-knot nematode (PRKN) Meloidogyne arenaria. Current resistant cultivars rely on a single introgression for PRKN resistance incorporated from the wild relative Arachis cardenasii, which could be overcome as a result of the emergence of virulent nematode populations. Therefore, new sources of resistance may be needed. Near-immunity has been found in the peanut wild relative Arachis stenosperma. The two loci controlling the resistance, present on chromosomes A02 and A09, have been validated in tetraploid lines and have been shown to reduce nematode reproduction by up to 98%. To incorporate these new resistance QTL into cultivated peanut, we used a marker-assisted backcrossing approach, using PRKN A. stenosperma-derived resistant lines as donor parents. Four cycles of backcrossing were completed, and SNP assays linked to the QTL were used for foreground selection. In each backcross generation seed weight, length, and width were measured, and based on a statistical analysis we observed that only one generation of backcrossing was required to recover the elite peanut’s seed size. A populating of 271 BC3F1 lines was genome-wide genotyped to characterize the introgressions across the genome. Phenotypic information for leaf spot incidence and domestication traits (seed size, fertility, plant architecture, and flower color) were recorded. Correlations between the wild introgressions in different chromosomes and the phenotypic data allowed us to identify candidate regions controlling these domestication traits. Finally, PRKN resistance was validated in BC3F3 lines. We observed that the QTL in A02 and/or large introgression in A09 are needed for resistance. This present work represents an important step toward the development of new high-yielding and nematode-resistant peanut cultivars.

Dickeya colocasiae sp. nov. isolated from wetland taro, Colocasia esculentum

Bacterial pathogens identified as Dickeya sp. have recently been associated with a corm rot of wetland taro on Oahu, Hawaii, but the species designation of these strains was unclear. A Gram-negative, pectinolytic bacterial strain PL65T isolated from an infected taro corm was subjected to polyphasic analysis to determine its genomic and phenotypic characteristics. Multi-locus sequence analyses (MLSA) based on five housekeeping genes (dnaA, gapA, gyrB, atpD, and purA) revealed that Dickeya zeae and D. oryzae, were the closest relatives. Phylogenetic analysis based on 463 core gene sequences clearly showed two potentially new species within Dickeya oryzae. In silico DNA-DNA hybridization value of strain PL65T with 12 Type strains of Dickeya species was <68%. Average nucleotide identity (ANI) analysis revealed that PL65T was at the margin of the species delineation cut-off values with a 96% ANI value. The metabolic profile of strain PL65T using BIOLOG differentiated it from the type strains of all other known species of Dickeya. Based on the results of genome-to-genome comparisons and phenotypic data presented in this report, we propose establishment of a new species, Dickeya colocasiae sp. nov. with strain PL65T as the type strain (ICMP 24361T).

Novel cysteine substitution p.(Cys1084Tyr) causes variable expressivity of qualitative and quantitative VWF defects

Von Willebrand factor (VWF) is an extremely cysteine-rich multimeric protein that is essential for maintaining normal hemostasis. The cysteine residues of VWF monomers form intra- and inter-molecular disulfide bonds that regulate its structural conformation, multimer distribution and ultimately its hemostatic activity. In this study we investigated and characterized the molecular and pathogenic mechanisms through which a novel cysteine variant p.(Cys1084Tyr) causes an unusual, mixed phenotype form of von Willebrand disease (VWD). Phenotypic data including bleeding scores, laboratory values, VWF multimer distribution and desmopressin response kinetics were investigated in 5 members (2 parents and 3 daughters) of a consanguineous family. VWF synthesis and secretion were also assessed in a heterologous expression system and in a transient transgenic mouse model. Heterozygosity for p.(Cys1084Tyr) was associated with variable expressivity of qualitative VWF defects. Heterozygous individuals had reduced VWF:GPIbM (&lt;0.40IU/mL) and VWF:CB (&lt;0.35IU/mL) as well as relative reductions in high-molecular weight multimers, consistent with type 2A VWD. In addition to these qualitative defects, homozygous individuals also displayed reduced FVIII:C/VWF:Ag leading to very low FVIII levels (0.03-0.1IU/mL) as well as reduced VWF:Ag (&lt;0.40IU/mL) and VWF:GPIbM (&lt;0.30IU/ml). Accelerated VWF clearance and impaired VWF secretion contributed to the fully expressed homozygous phenotype with impaired secretion arising due to disordered disulfide connectivity.

SoyFGB v2.0: a unique access to variations of Chinese Soybean Gene Bank (CNSGB) germplasm

In Chinese National Soybean GeneBank (CNSGB), we have collected more than 30,000 soybean accessions. However, data sharing for soybean remains an especially sensitive question, and how to share the genome variations within rule frame has been bothering the soybean germplasm workers for a long time. Here we release a big data source named Soybean Functional Genomics & Breeding database (SoyFGB v2.0) (https://sfgb.rmbreeding.cn/), which embed a core collection of 2,214 soybean resequencing genome (2K-SG) from the CNSGB germplasm. This source presents a unique example which may help elucidating the following three major functions for multiple genome data mining with general interests for plant researchers. 1) On-line analysis tools are provided by the Analysis module for haplotype mining in high-throughput genotyped germplasms with different methods. 2) Variations for 2K-SG are provided in SoyFGB v2.0 by Browse module which contains two functions of SNP and InDel. Together with the Gene (SNP & InDel) function embedded in Search module, the genotypic information of 2K-SG for targeting gene / region is accessible. 3) Scaled phenotype data of 42 traits, including 9 quality and 33 quantitative traits are provided by SoyFGB v2.0. With the scaled-phenotype data search and seed request tools under a control list, the germplasm information could be shared without direct downloading the unpublished phenotypic data or information of sensitive germplasms. In a word, the mode of data mining and sharing underlies SoyFGB v2.0 may inspire more ideas for works on genome resources of not only soybean but also the other plants.

Environment-Specific Genomic Prediction Ability in Maize Using Environmental Covariates Depends on Environmental Similarity To Training Data

Technology advances have made possible the collection of a wealth of genomic, environmental, and phenotypic data for use in plant breeding. Incorporation of environmental data into environment-specific genomic prediction (GP) is hindered in part because of inherently high data dimensionality. Computationally efficient approaches to combining genomic and environmental information may facilitate extension of GP models to new environments and germplasm, and better understanding of genotype-by-environment (G × E) interactions. Using genomic, yield trial, and environmental data on 1,918 unique hybrids evaluated in 59 environments from the maize Genomes to Fields project, we determined that a set of 10,153 SNP dominance coefficients and a 5-day temporal window size for summarizing environmental variables were optimal for GP using only genetic and environmental main effects. Adding marker-by-environment variable interactions required dimension reduction, and we found that reducing dimensionality of the genetic data while keeping the full set of environmental covariates was best for environment-specific GP of grain yield, leading to an increase in prediction ability of 2.7% to achieve a prediction ability of 80% across environments when data were masked at random. We then measured how prediction ability within environments was affected under stratified training-testing sets to approximate scenarios commonly encountered by plant breeders, finding that incorporation of marker-by-environment effects improved prediction ability in cases where training and test sets shared environments, but did not improve prediction in new untested environments. The environmental similarity between training and testing sets had a greater impact on the efficacy of prediction than genetic similarity between training and test sets.

Genomic evidence of speciation by fusion linked to trophic niche expansion in a recent radiation of grasshoppers

Post-divergence gene flow can trigger a number of creative evolutionary outcomes, ranging from the transfer of beneficial alleles across species boundaries (i.e., adaptive introgression) to the formation of new species (i.e., hybrid speciation). While neutral and adaptive introgression has been broadly documented in nature, hybrid speciation is assumed to be rare and the evolutionary and ecological context facilitating this phenomenon still remains controversial. Through combining genomic and phenotypic data, we evaluate the hypothesis that the dual feeding regime (scrub legumes and gramineous herbs) of the taxonomically controversial grasshopper Chorthippus saulcyi algoaldensis resulted from hybridization between two sister taxa that exhibit contrasting host-plant specializations: C. binotatus (scrub legumes) and C. saulcyi (gramineous herbs). Genetic clustering analyses and inferences from coalescent-based demographic simulations confirmed that C. s. algoaldensis represents a uniquely evolving lineage and supported the ancient hybrid origin of this taxon (ca. 1.4 Ma), which provides a mechanistic explanation for its broader trophic niche and sheds light on its uncertain phylogenetic position. We propose a Pleistocene hybrid speciation model where range shifts resulting from climatic oscillations can promote the formation of hybrid swarms and facilitate its long-term persistence through geographic isolation from parental forms in topographically complex landscapes.

Discovery of Single Nucleotide Polymorphisms for Resistance to Abnormal Vertical Growth in Macadamia

Abnormal vertical growth (AVG) syndrome is a serious threat to the Australian macadamia industry as it decreases the yield of nuts by as much as 70% per annum. A lack of information on the cause of AVG has hindered the development of an effective disease management strategy. Discovery of genetic markers associated with disease resistance can be used as tool for rapid selection of elite cultivars, hence helps in efficient disease management. Differences in field susceptibility of macadamia cultivars provide an opportunity for discovery of genetic markers that are associated with host resistance. REML mixed model analysis was performed to estimate the AVG rating of 51 cultivars from multiple origins using phenotypic data from 359 trees planted in four sites. Most of the Hawaiian cultivars were found as susceptible, while selections from the Australian macadamia industry breeding program were predominantly resistant. All the cultivars were genotyped for 13,221 DArTseq-based single nucleotide polymorphism (SNP) markers. A bulked sample analysis was performed using 20 genotypes each at the extremes of AVG phenotypic ratings. Ten SNP markers were predicted to be associated with AVG resistance and two arbitrarily selected SNP markers were validated using PCR and Sanger sequencing. Our findings suggest that AVG resistance in the commercial cultivars may be derived from the genomic introgression of Macadamia tetraphylla through interspecific hybridization. The results may support marker-assisted selection for macadamia germplasm with AVG resistance.

Characterization of antibiotic resistance in clinical isolates of Klebsiella pneumoniae in Denmark

Klebsiella pneumoniae (KP) is a major global health problem as it leads to hospital outbreaks all over the world and is becoming more difficult to treat due to its increasing antimicrobial resistance (AMR). Optimization and development of new treatments of KP requires understanding of its population structure and AMR properties. Therefore, in this study, we collected and sequenced 491 KP strains from four major Danish microbiology departments covering 51% of the Danish population. The isolates were whole genome sequenced (WGS), phenotypically characterized and compared with 2,124 KP strains from 13 different countries (PATRIC strains). We found that while genomic content varies significantly across the Danish strains, they also differ significantly from strains from other countries, due to the lack of certain AMR sequence types (e.g. ST258 and ST307) in Denmark. Genomic and experimental analysis suggest that Danish strains contain fewer virulence mechanisms and are more susceptible to antimicrobials compared to strains from other countries, likely due to the relatively low antibiotic usage in Denmark where 70% of hospital antibiotic usage is penicillins. We also identified potential novel AMR determinants to tigecycline through statistical analysis of genomic and phenotypic data. To conclude, we obtained a more comprehensive understanding of the KP strains in Denmark and provided valuable insights for future experiments and strategies to combat AMR in KP.

Validation of molecular markers linked to Cercospora leaf spot disease resistance in mungbean (Vigna radiata [L.] Wilczek)

Cercospora leaf spot (CLS) resistance is a highly desirable trait for mungbean (Vigna radiata [L.] Wilczek) production in Thailand. ‘V4718’ is a vital resistance source that shows high and stable resistance to CLS disease. A previous study identified a major quantitative trait locus (QTL) (qCLSC72V18-1) controlling CLS resistance and found the marker (I16274) that was located closest to the resistance gene by using F2:9 and F2:10 recombinant inbred line populations derived through a cross between ‘V4718’ and the susceptible variety ‘Chai Nat 72’ (‘CN72’). Here, we evaluated three newly reported simple sequence repeat (SSR) markers and one InDel marker together with six previously identified markers that were linked to qCLSC72V18-1 to further identify the markers that were located close to this QTL. By performing bulk segregant analysis on two validation populations, we found that two SSR markers (Vr6gCLS037 and Vr6gCLS133) and one InDel marker (VrTAF5_indel) were putatively associated with CLS resistance. Of these markers, only the VrTAF5_indel marker showed a significant association with the CLS resistance gene with a logarithm of odds score > 3 across the phenotypic data for 2016 and 2018. QTL analysis with inclusive composite interval mapping revealed that the VrTAF5_indel marker was integrated into the genetic map with other previously identified markers. The I16274 and VrTAF5_indel markers flanking the QTL of interest accounted for 41.56%-60.38% of the phenotypic variation with genetic distances of 4.0 and 5.0 cM from the resistance gene, respectively. Both markers together permitted only 0.40% recombination with the CLS resistance gene in marker-assisted selection and thus could be useful in future breeding efforts for CLS resistance in mungbean.