Biology subjects

Roper, M. C.

Publications and source records attributed to Roper, M. C..

4 recordsLinked to original sources

bioRxiv2023

Permethylation as a Strategy for High Molecular Weight Polysaccharide Structure Analysis by NMR& Case Study of Xylella fastidiosa EPS

Current practices for structure analysis of extremely large molecular weight polysaccharides via solution-state NMR spectroscopy incorporate partial depolymerization protocols that enable polysaccharide solubilization in suitable solvents. Non-specific depolymerization techniques utilized for glycosidic bond cleavage, such as chemical degradation or ultrasonication, potentially generate structure fragments that can complicate the complete characterization of polysaccharide structures. Utilization of appropriate enzymes for polysaccharide degradation, on the other hand, requires prior structure information and optimal enzyme activity conditions that are not available to the analyst working with novel or unknown compounds. Herein, we describe the application of a permethylation strategy that allows the complete dissolution of the intact polysaccharides for NMR structure characterization. This approach is utilized for NMR analysis of Xylella fastidiosa EPS, which is essential for the virulence the plant pathogen that affects multiple commercial crops and is responsible for multibillion dollar losses each year.

biochemistry↗

bioRxiv2022

Using genomes and evolutionary analyses to screen for host-specificity and arms-race dynamics in the plant pathogen Xylella fastidiosa

Xylella fastidiosa infects several economically important crops in the Americas, and it also recently emerged in Europe. Here, using a set of Xylella genomes reflective of the genus-wide diversity, we performed a pan-genome analysis based on both core and accessory genes, for two purposes: i) to test associations between genetic divergence and plant host species and ii) to identify positively selected genes that are potentially involved in arms-race dynamics. For the former, tests yielded significant evidence for specialization of X. fastidiosa to plant host species. This observation contributes to a growing literature suggesting that the phylogenetic history of X. fastidiosa lineages affects host range. For the latter, our analyses uncovered evidence of positive selection across codons for 5.3% (67 of 1,257) of core genes and 5.4% (201 of 3,691) of accessory genes; these genes are candidates to encode interacting factors with plant and insect hosts. Most of these genes had unknown functions, but we identified some tractable candidates including nagZ_2, which encodes a beta-glucosidase that is important for Neisseria gonorrhoeae biofilm formation; cya, which modulates gene expression in pathogenic bacteria; and barA, a membrane associated histidine kinase that has roles in cell division, metabolism, and pili formation. ABSTRACT IMPORTANCEXylella fastidiosa causes devasting diseases to several critical crops. Because X. fastidiosa colonizes and infects many plant species, it is important to understand whether the genome of X. fastidiosa has genetic determinants that underlie specialization to specific host plants. We analyzed genome sequences of X. fastidiosa to investigate evolutionary relationships and to test for evidence of positive selection on specific genes. We found a significant signal between genome diversity and host plants, consistent with bacterial specialization to specific plant hosts. By screening for positive selection, we identified both core and accessory genes that may affect pathogenicity, including genes involved in biofilm formation.

microbiology↗

bioRxiv2022

Arbuscular mycorrhizal fungal composition across US citrus orchards, management strategies, and disease severity spectrum

Arbuscular mycorrhizal fungi (AMF) remain understudied in perennial cropping systems. Citrus is a globally grown fruit tree and under threat by the pandemic Huanglongbing (HLB) disease. Here, we assessed in what capacity geographical location, management strategies and disease affect AMF citrus root communities. Root samples were collected from 88 trees in ten orchards located in the two major citrus producing states in the US. Orchards were selected based on conventional or organic practices in California and based on HLB symptom severity in Florida. We used AMF-specific amplicon sequencing primers to capture community composition and diversity. Taxa names were assigned based on a phylogenetic analysis that comprised a backbone of AMF references sequences from Mycobank and virtual taxa from the MaarjAM database. AMF were detected in 78% of citrus root samples with taxa belonging to six known (Dominikia, Funneliformis, Glomus, Rhizophagus, Sclerocystis, Septoglomus) and unknown Glomeraceae genera. Geographical location affected AMF community composition but not richness, whereas management practice and disease influenced both richness and composition. Our approach indicated that perennial agroecosystems share a set of AMF generalist and specialist taxa. Some taxa could improve environmental fitness and be exploited for agricultural purposes.

microbiology↗

bioRxiv2022

Microbial turnover and dispersal events occur in sync with plant phenology in the perennial evergreen tree crop, Citrus sinensis

Emerging research indicates that plant-associated microbes can alter plant developmental timing. However, it is unclear if host phenology impacts microbial community assembly. Microbiome studies in annuals or deciduous perennial plants face challenges in separating effects of tissue age from phenological driven effects on the microbiome. In contrast, evergreen perennial trees, like Citrus sinensis, retain leaves for years allowing for uniform sampling of similarly aged leaves from the same developmental cohort. This aids in separating phenological effects on the microbiome from impacts due to annual leaf maturation/senescence. Here we used this system to test the hypothesis that host phenology acts as a driver of microbiome composition. Citrus sinensis leaves and roots were sampled during seven phenological stages. Using amplicon-based sequencing, followed by diversity, phylogenetic, differential abundance, and network analyses we examined changes in bacterial and fungal communities. Host phenological stage is the main determinant of microbiome composition, particularly within the foliar bacteriome. Microbial enrichment/depletion patterns suggest that microbial turnover and dispersal were driving these shifts. Moreover, a subset of community shifts were phylogenetically conserved across bacterial clades suggesting that inherited traits contribute to microbe-microbe and/or plant-microbe interactions during specific phenophases. Plant phenology influences microbial community composition. These findings enhance understanding of microbiome assembly and identify microbes that potentially influence plant development and reproduction.

microbiology↗