Anthony E. Melton
Publications (Showing 5 of 7)
Exploring sagebrush leaf microbial metagenomes from deep, host-derived sequencing
Vol. 14, Issue 5
ABSTRACT
Advanced sequencing technologies and improvements in bioinformatics have provided a new way to study plant-associated microbial communities, including the use of host genomic sequencing. Our study focuses on the leaf microbiome of basin big sagebrush ( Artemisia tridentata
subsp. tridentata ), a foundational shrub of western North America. We analyzed Illumina shotgun sequences from sagebrush leaves to investigate the metagenomes of leaf-associated microbes that were sequenced alongside their plant hosts. We aimed to profile the leaf microbiome across different sample sources (magenta box, greenhouse, and field/wild), reconstruct metagenome-assembled genomes (MAGs) where possible, and investigate functional gene annotations of the resulting MAGs, specifically with regard to the potential metabolism of sagebrush chemicals. To achieve this, Illumina shotgun sequence reads (containing both host and associated microbial reads) were mapped to the reference genomes of Artemisia tridentata , Artemisia annua , and the human reference genome to remove plant host and human-associated sequences. Host-cleaned reads were then analyzed using microbial metagenomics techniques. Taxonomic profiling revealed that Phyllobacterium and Sphingomonas were the most abundant microbial genera in greenhouse-grown plants, with very little variation among the samples. Wild, field-collected samples were much more variable and were dominated by Klebsiella and Aureobasidium species. From the co-assembly of greenhouse samples, we reconstructed two high-quality MAGs (a Phyllobacterium species and a Sphingomonas species) with >98% completion and <1% contamination. Functional annotation of these MAGs uncovered genes associated with the degradation and metabolism of camphor and other essential oils such as pinene, geraniol, and limonene, which are part of sagebrush leaf chemistry.IMPORTANCE
Big sagebrush ( Artemisia tridentata
), the foundation species of the sagebrush steppe, has broad ecological importance because its evergreen leaves offer nutrients and shade that facilitate the establishment of diverse understory plants in arid environments. Sagebrush leaves contain various secondary metabolites, including terpenoids, flavonoids, and phenolic compounds. These chemicals contribute to the plant’s defense mechanisms against herbivores and pathogens. Despite this, sagebrush hosts diverse bacterial and fungal communities. We found that the microbial metagenome-assembled genomes (MAGs) we recovered contained genes that have the potential to degrade some of the chemical compounds in sagebrush leaves that could inhibit the growth of other microbes. This is the first study to mine plant genome data using host-derived sequences to generate microbial MAGs. Our results showed that MAGs can be recovered from plant host-derived sequence data, providing a new way to explore the identity and functional capabilities of difficult-to-culture microbes.DOI:
10.1128/spectrum.02198-25
Utilizing a comparative approach to assess genome evolution during diploidization in Artemisia tridentata, a keystone species of western North America
Vol. 111, Issue 6
Premise
Polyploidization is often followed by diploidization. Diploidization is generally studied using synthetic polyploid lines and/or crop plants, but rarely using extant diploids or nonmodel plants such as Artemisia tridentata. This threatened western North American keystone species has a large genome compared to congeneric Artemisia species; dominated by diploid and tetraploid cytotypes, with multiple origins of tetraploids with genome size reduction.
Methods
The genome of an A. tridentata sample was resequenced to study genome evolution and compared to that of A. annua, a diploid congener. Three diploid genomes of A. tridentata were compared to test for multiple diploidization events.
Results
The A. tridentata genome had many chromosomal rearrangements relative to that of A. annua, while large‐scale synteny of A. tridentata chromosome 3 and A. annua chromosome 4 was conserved. The three A. tridentata genomes had similar sizes (4.19–4.2 Gbp), heterozygosity (2.24–2.25%), and sequence (98.73–99.15% similarity) across scaffolds, and in k‐mer analyses, similar patterns of diploid heterozygous k‐mers (AB = 41%, 47%, and 47%), triploid heterozygous k‐mers (AAB = 18–21%), and tetraploid k‐mers (AABB = 13–17%). Biallelic SNPs were evenly distributed across scaffolds for all individuals. Comparisons of transposable element (TE) content revealed differential enrichment of TE clades.
Conclusions
Our findings suggest population‐level TE differentiation after a shared polyploidization‐to‐diploidization event(s) and exemplify the complex processes of genome evolution. This research approached provides new resources for exploration of abiotic stress response, especially the roles of TEs in response pathways.
DOI:
10.1002/ajb2.16353
A genotype × environment experiment reveals contrasting response strategies to drought between populations of a keystone species (Artemisia tridentata; Asteraceae)
Vol. 4, Issue 4
pp. 201-214
Abstract
Western North America has been experiencing persistent drought exacerbated by climate change for over two decades. This extreme climate event is a clear threat to native plant communities. Artemisia tridentata is a keystone shrub species in western North America and is threatened by climate change, urbanization, and wildfire. A drought Genotype × Environment (G × E) experiment was conducted to assess phenotypic plasticity and differential gene expression in A. tridentata. The G × E experiment was performed on diploid A. tridentata seedlings from two populations (one from Idaho, USA and one from Utah, USA), which experience differing levels of drought stress during the summer months. Photosynthetic data, leaf temperature, and gene expression levels were compared between treatments and populations. The Utah population maintained higher photosynthetic rates and photosynthetic efficiency than the Idaho population under drought stress. The Utah population also exhibited far greater transcriptional plasticity than the Idaho population and expressed genes of response pathways distinct from those of the Idaho population. Populations of A. tridentata differ greatly in their drought response pathways, likely due to differences in response pathways that have evolved under distinct climatic regimes. Epigenetic processes likely contribute to the observed differences between the populations.
DOI:
10.1002/pei3.10119
A haploid pseudo-chromosome genome assembly for a keystone sagebrush species of western North American rangelands
Vol. 12, Issue 7
Increased ecological disturbances, species invasions, and climate change are creating severe conservation problems for several plant species that are widespread and foundational. Understanding the genetic diversity of these species and how it relates to adaptation to these stressors are necessary for guiding conservation and restoration efforts. This need is particularly acute for big sagebrush (Artemisia tridentata; Asteraceae), which was once the dominant shrub over 1,000,000 km2 in western North America but has since retracted by half and thus has become the target of one of the largest restoration seeding efforts globally. Here, we present the first reference-quality genome assembly for an ecologically important subspecies of big sagebrush (A. tridentata subsp. tridentata) based on short and long reads, as well as chromatin proximity ligation data analyzed using the HiRise pipeline. The final 4.2-Gb assembly consists of 5,492 scaffolds, with nine pseudo-chromosomal scaffolds (nine scaffolds comprising at least 90% of the assembled genome; n = 9). The assembly contains an estimated 43,377 genes based on ab initio gene discovery and transcriptional data analyzed using the MAKER pipeline, with 91.37% of BUSCOs being completely assembled. The final assembly was highly repetitive, with repeat elements comprising 77.99% of the genome, making the Artemisia tridentata subsp. tridentata genome one of the most highly repetitive plant genomes to be sequenced and assembled. This genome assembly advances studies on plant adaptation to drought and heat stress and provides a valuable tool for future genomic research.
DOI:
10.1093/g3journal/jkac122
Meta-analysis reveals challenges and gaps for genome-to-phenome research underpinning plant drought response
Vol. 23, Issue 20
pp. 12297
Severe drought conditions and extreme weather events are increasing worldwide with climate change, threatening the persistence of native plant communities and ecosystems. Many studies have investigated the genomic basis of plant responses to drought. However, the extent of this research throughout the plant kingdom is unclear, particularly among species critical for the sustainability of natural ecosystems. This study aimed to broaden our understanding of genome-to-phenome (G2P) connections in drought-stressed plants and identify focal taxa for future research. Bioinformatics pipelines were developed to mine and link information from databases and abstracts from 7730 publications. This approach identified 1634 genes involved in drought responses among 497 plant taxa. Most (83.30%) of these species have been classified for human use, and most G2P interactions have been described within model organisms or crop species. Our analysis identifies several gaps in G2P research literature and database connectivity, with 21% of abstracts being linked to gene and taxonomy data in NCBI. Abstract text mining was more successful at identifying potential G2P pathways, with 34% of abstracts containing gene, taxa, and phenotype information. Expanding G2P studies to include non-model plants, especially those that are adapted to drought stress, will help advance our understanding of drought responsive G2P pathways.
DOI:
10.3390/ijms232012297