Biology subjects

Adams, T. M.

Publications and source records attributed to Adams, T. M..

7 recordsLinked to original sources

bioRxiv2025

Phased Potato Genome Assembly and Association Genetics Enable Characterisation of the Elusive H1 Resistance Locus Against Potato Cyst Nematodes

The complexity of potato genetics, characterised by tetrasomic inheritance, has contributed to slower genetic gain in potato compared to other major crops. Disease resistance genes, often found in large clusters of highly similar paralogs and alleles, further complicate genetic studies. The H1 resistance locus, introgressed into potato cultivars from Solanum tuberosum spp. andigena, has been successfully used for over 60 years to control Globodera rostochiensis in Europe. Although previous genetic studies mapped this resistance to chromosome 5, the complete structure of the locus remained elusive. To reduce genomic complexity, we generated a dihaploid of the cultivar Athlete, DH4_Athlete, carrying the H1 resistance locus, and produced a phased haplotype representation of the H1 interval using Oxford Nanopore sequencing. Combined with RenSeq-based association genetics, this approach allowed us to reconstruct the entire H1 locus, including recombination points at both the 5' and 3' ends of the interval.

plant biology↗

bioRxiv2025

Molecular mechanisms of immune evasion by host protein glycosylation of a bacterial immunogen used in nucleic acid vaccines

Nucleic acid vaccines (DNA and mRNA) induce immunity by driving in situ antigen expression in host cells. For non-viral pathogens, however, host expression can impose post-translational modifications absent from the native microbial antigen. Tuberculosis (TB) remains a leading cause of infectious mortality, and nucleic acid vaccines targeting the Mycobacterium tuberculosis antigen 85 (Ag85) complex did not confer protective efficacy in clinical trials. We hypothesized that host-derived N-glycosylation of Ag85 immunogens expressed in mammalian cells compromises immune recognition. Here, we define structural, biochemical and immunological mechanisms by which host-imposed N-glycosylation remodels a bacterial antigen expressed in mammalian cells. We show that Ag85B expressed in human Expi293 cells is microheterogeneously N-glycosylated at four canonical sequons (N52, N224, N234, N280) with predominantly complex, highly fucosylated, and frequently sialylated glycans. Molecular dynamics simulations indicate that these glycans occupy substantial conformational space and reduce solvent and antibody-accessible surface area, occluding multiple established B-cell and T-cell epitope regions. Consistent with glycan-mediated shielding, mammalian-expressed Ag85B shows markedly reduced binding to an Ag85-complex monoclonal antibody by competitive ELISA and biolayer interferometry, and sialylated glycans enable Siglec-9 binding that is abrogated by sialidase treatment. Together, these findings define the structural and biochemical mechanisms by which host glycosylation can remodel bacterial vaccine antigens, supporting glycosylation-aware immunogen engineering as a design principle for nucleic acid vaccines targeting non-viral pathogens.

biochemistry↗

bioRxiv2024

Transcriptional profiling during infection of potato NLRs and Phytophthora infestans effectors using cDNA enrichment sequencing

An accurate assessment of host and pathogen gene expression during infection is critical for understanding the molecular aspects of host-pathogen interactions. Often, pathogen-derived transcripts are difficult to ascertain at early infection stages owing to the unfavourable transcript representation compared to the host genes. In this study, we compare two sequencing techniques, RNAseq and enrichment sequencing (RenSeq and PenSeq) of cDNA, to investigate gene expression patterns in the doubled monoploid potato (DM) infected with the late blight pathogen Phytophthora infestans. Our results reveal distinct advantages of cDNA RenSeq and PenSeq over traditional RNAseq in terms of target gene representation and transcriptional quantification at early infection stages. Throughout the infection time course, cDNA enrichment sequencing enables transcriptomic analyses for more targeted host and pathogen genes. For highly expressed genes that were sampled in parallel by both cDNA enrichment and RNAseq, a high level of concordance in expression profiles is observed, indicative of at least semi-quantitative gene expression representation following enrichment.

molecular biology↗

bioRxiv2022

SMRT-AgRenSeq-d in potato (Solanum tuberosum) identifies candidates for the nematode resistance Gpa5

Potato is the third most important food crop in the world. Diverse pathogens threaten sustainable crop production but can be controlled, in many cases, through the deployment of disease resistance genes belonging to the family of nucleotide-binding, leucine-rich-repeat (NLR) genes. To identify functional NLRs in established varieties, we have successfully established SMRT-AgRenSeq in tetraploid potatoes and have further enhanced the methodology by including dRenSeq in an approach that we term SMRT-AgRenSeq-d. The inclusion of dRenSeq enables the filtering of candidates after the association analysis by establishing a presence/absence matrix across resistant and susceptible potatoes that is translated into an F1 score. Using a SMRT-RenSeq based sequence representation of the NLRome from the cultivar Innovator, SMRT-AgRenSeq-d analyses reliably identified the late blight resistance benchmark genes R1, R2-like, R3a and R3b in a panel of 117 varieties with variable phenotype penetrations. All benchmark genes were identified with an F1 score of 1 which indicates absolute linkage in the panel. When applied to the elusive nematode disease resistance gene Gpa5 that controls the Potato Cyst Nematode (PCN) species Globodera pallida (pathotypes Pa2/3), SMRT-AgRenSeq-d identified nine strong candidates. These map to the previously established position on potato chromosome 5 and are potential homologs of the late blight resistance gene R1. Assuming that NLRs are involved in controlling many types of resistances, SMRT-AgRenSeq-d can readily be applied to diverse crops and pathogen systems. In potato, SMRT-AgRenSeq-d lends itself, for example, to further study the elusive PCN resistances H1 or H3 for which phenotypic data exist.

plant biology↗

bioRxiv2022

HISS: Snakemake-based workflows for performing SMRT-RenSeq assembly, AgRenSeq and dRenSeq for the discovery of novel plant disease resistance genes.

BackgroundIn the ten years since the initial publication of the RenSeq protocol, the method has proved to be a powerful tool for studying disease resistance in plants and providing target genes for breeding programmes. Since the initial publication of the methodology, it has continued to be developed as new technologies have become available and the increased availability of computing power has made new bioinformatic approaches possible. Most recently, this has included the development of a k-mer based association genetics approach, the use of PacBio HiFi data, and graphical genotyping with diagnostic RenSeq. However, there is not yet a unified workflow available and researchers must instead configure approaches from various sources themselves. This makes reproducibility and version control a challenge and limits the ability to perform these analyses to those with bioinformatics expertise. ResultsHere we present HISS, consisting of three workflows which take a user from raw RenSeq reads to the identification of candidates for disease resistance genes. These workflows conduct the assembly of enriched HiFi reads from an accession with the resistance phenotype of interest. A panel of accessions both possessing and lacking the resistance are then used in an association genetics approach (AgRenSeq) to identify contigs positively associated with the resistance phenotype. Candidate genes are then identified on these contigs and assessed for their presence or absence in the panel with a graphical genotyping approach that uses dRenSeq. These workflows are implemented via Snakemake, a python-based workflow manager. Software dependencies are either shipped with the release or handled with conda. All code is freely available and is distributed under the GNU GPL-3.0 license. ConclusionsHISS provides a user-friendly, portable, and easily customised approach for identifying novel disease resistance genes in plants. It is easily installed with all dependencies handled internally or shipped with the release and represents a significant improvement in the ease of use of these bioinformatics analyses.

bioinformatics↗

bioRxiv2022

Sequential in vitro enzymatic N-glycoprotein modification reveals site-specific rates of glycoenzyme processing

N-glycosylation is an essential eukaryotic post-translational modification that affects various glycoprotein properties, including folding, solubility, protein-protein interactions, and half-life. N-glycans are processed in the secretory pathway to form varied ensembles of structures, and diversity at a single site on a glycoprotein is termed microheterogeneity. To understand the factors that influence glycan microheterogeneity, we hypothesized that local steric and electrostatic factors surrounding each site influences glycan availability to enzymatic modification. We tested this hypothesis by expression of a panel of reporter N-linked glycoproteins in MGAT1- null HEK293 cells to produce immature Man5GlcNAc2 glycoforms (38 glycan sites total). These glycoproteins were then sequentially modified in vitro from high-mannose to hybrid and on to biantennary, core fucosylated, complex structures by a panel of N-glycosylation enzymes and each reaction time-course was quantified by LC-MS/MS. Substantial differences in rates of in vitro enzymatic modification were observed between glycan sites on the same protein and differences in modification rates varied depending on the glycoenzyme being evaluated. By comparison, proteolytic digestion of the reporters prior to N-glycan processing eliminated differences in in vitro enzymatic modification. Comparison of in vitro rates of enzymatic modification with the glycan structures found on the mature reporters expressed in wild type cells correlate well with the enzymatic bottlenecks found in vitro. These data suggest that higher-order local structures surrounding each glycosylation site contribute to the efficiency of modification both in vitro and in vivo to establish the spectrum of site-specific microheterogeneity found on N-linked glycoproteins.

biochemistry↗

bioRxiv2019

Genomic investigation of the strawberry pathogen Phytophthora fragariae indicates pathogenicity is determined by transcriptional variation in three key races

The oomycete Phytophthora fragariae is a highly destructive pathogen of cultivated strawberry (Fragaria x ananassa), causing the root rotting disease, red core. The host-pathogen interaction has a well described gene-for-gene resistance relationship, but to date neither candidate avirulence nor resistance genes have been identified. We sequenced a set of American, Canadian and UK isolates of known race type, along with three representatives of the closely related pathogen of the raspberry (Rubus idaeus), Phytophthora rubi, and found a clear population structure, with a high degree of nucleotide divergence seen between some race types and abundant private variation associated with race types 4 and 5. In contrast, between isolates defined as UK races 1, 2 & 3 (UK1-2-3) there was no evidence of gene loss or gain; or the presence of insertions/deletions (INDELs) or Single Nucleotide Polymorphisms (SNPs) within or in proximity to putative pathogenicity genes could be found associated with race variation. Transcriptomic analysis of representative UK1-2-3 isolates revealed abundant expression variation in key effector family genes associated with pathogen race; however, further long read sequencing did not reveal any long range polymorphisms to be associated with avirulence to race UK2 or UK3 resistance, suggesting either control in trans or other stable forms of epigenetic modification modulating gene expression. This work reveals the combined power of population resequencing to uncover race structure in pathosystems and in planta transcriptomic analysis to identify candidate avirulence genes. This work has implications for the identification of putative avirulence genes in the absence of associated expression data and points towards the need for detailed molecular characterisation of mechanisms of effector regulation and silencing in oomycete plant pathogens.

genomics↗