Biology subjects

Butchacas, J.

Publications and source records attributed to Butchacas, J..

9 recordsLinked to original sources

bioRxiv2026

An infection assay recapitulating Xanthomonas translucens pv. translucens natural entry into barley hydathodes

Pathogenic bacteria navigate biological host landscapes to enter and establish infection. How Xanthomonas phytopathogenic bacteria enter specific plant tissues is believed to directly determine the systemic vs. local outcome of infection. Non-vascular Xanthomonas infect leaf mesophyll locally from stomatal pores, while vascular ones enter through hydathode water pores on the leaf margin before invading the xylem for systemic movement. The pathovar Xanthomonas translucens pv. translucens (Xtt) is associated with barley infection, causing both bacterial leaf streak and bacterial blight symptoms by colonizing both the mesophyll spaces through stomatal guard cells and the plant vasculature, respectively. How Xtt reaches the vasculature in barley leaves is yet to be established. In this study, we determined the anatomy of barley hydathodes. A protocol allowing efficient hydathode infection by Xtt was established and caused bacterial blight symptoms, closely mimicking the natural infection process. This study establishes Xtt as one of the few demonstrated hydathode pathogens.

plant biology↗

bioRxiv2025

Effector loss and gain drives pathogen host range at a fitness cost

Epidemic preparedness depends on tracking microbial evolution that drives shifts in ecological behaviors such as disease emergence. However, the genetic constraints for microbial host adaptation to emerge for generalist and specialist behaviors remain poorly described. Here, we show that generalist cereal pathogen Xanthomonas translucens arose from a specialist ancestor via the loss of a single effector gene, xopAL1. Deleting barley-specialist X. translucens xopAL1 recapitulated the host jump to wheat and demonstrates risk across each globally distributed genetic lineage. However, this niche expansion via XopAL1 loss incurs a significant pathogenic fitness cost to colonize barley. Moreover, the specialist lineage gained an additional effector gene, xopAJ, which enhanced virulence on barley while restricting oat infection, thereby reinforcing niche specialization. We further identified key host pathways mediating resistance to the specialist lineage of X. translucens, opening avenues for potentially identifying targets for crop improvement. Our work provides an experimentally validated evolutionary framework to understand mechanisms of intergenera host jump. Overall, we demonstrate that single events of gene loss and gain shape ecological behaviors of pathogens by creating a dynamic trade-off between niche breadth and specialization.

microbiology↗

bioRxiv2025

Ecological ubiquity and phylogeny drive nestedness in phages-bacteria networks and shape the bacterial defensome

Identifying the ecological and evolutionary factors that shape phage-bacterial interactions is key to understanding their dynamics in microbial communities. Yet, such interactions remain poorly characterised in plant agroecosystems. Here, we investigate the ecological determinants of the interaction between a highly diverse set of 23 phages isolated from diseased apricot trees and 44 bacterial strains from the Pseudomonas syringae species complex collected either from diseased apricot trees, healthy plants or non-agricultural environment. Based on their ecological origin, we expected phages to preferentially infect bacterial strains from the same ecological context, forming modular host-range patterns. Contrary to these expectations, we discovered a significantly nested structure, suggesting generalised infection dynamics rather than local adaptation, primarily driven by the broad ecological dynamics of this pathosystem. Analysis of the bacterial genomes showed that both the profiles of anti-phage defence systems and the distribution profiles of prophages are strongly shaped by bacterial phylogeny. Furthermore, while the number of defence systems showed limited correlation with the breadth of bacterial sensitivity to phages, prophage abundance exhibited a strong, non-linear link with phage virulence. Together, these findings provide an ecological and evolutionary perspective on phage-bacterium infection networks and new insights into a better understanding of the role of phages in agricultural ecosystems. Author SummaryViruses that infect bacteria, known as phages, are part of microbial communities and influence the abundance, diversity, and traits of their hosts. In an agriculture-related context, they are commonly considered as potential biocontrol agents, but studying the bases of fundamental phage-bacterial interactions may help us better understand the plant microbiome and its applications. Many factors influence these interactions, and identifying which ones matter most remains a challenge. In our study, we investigated how phages from diseased plants interact with bacteria collected from diseased and healthy plants, as well as from surrounding environments. We expected phages to mainly infect bacteria from similar environments, but instead observed that they often infected bacteria regardless of their source. This suggests that phage activity in this system has few barriers, reflecting the wide ecological distribution of their bacterial hosts. We further investigated how bacteria defend against phages by identifying both defence systems and prophages within their genomes and using this information to explore their contribution to bacterial resistance or sensitivity to phages. Together, our findings offer new insights into how phage-bacterium relationships evolve and function in plant ecosystems.

ecology↗

bioRxiv2025

Identification of Halo Blight Disease on Oat in Idaho and Exploration of Resistant Sources in Oat, Barley and Wheat

Pseudomonas coronafaciens pv. coronafaciens (Pcc), the causal agent of Bacterial Halo blight (BHB) on oat, has been infrequently reported in the United States, with historical records limited to the 1920s through the 1960s. In 2023, oat trial fields in Aberdeen, Idaho were severely infected with an unknown disease that formed necrotic lesions on leaves. Preliminary identification based on colony morphology suggested a pathogen belonging to the genus Pseudomonas. Subsequent whole-genome sequencing confirmed 99.6% average nucleotide identity (ANI) with Pseudomonas coronafaciens pv. coronafaciens (Pcc). This marks the first detection of Pcc in Idaho, and the first detailed description of the pathogen in the United States after over half a century. Host range and pathogenicity assessments on multiple cereal crops showed that Pcc was pathogenic on oat, barley, and corn. However, wheat, rye and triticale displayed chlorosis and early cell death in response to the pathogen. Evaluation of oat and barley genotypes revealed resistance in the two crop species to be rare with only 2.5, and 4.5% of oat and barley genotypes exhibiting some level of resistance. Notably, the four resistant and moderately resistant barley genotypes identified in this study: DH170472, Celebration, Legacy and Quest are the first to be reported as sources of resistance to BHB. Results of the present study provides a basis for further research toward a better understanding of disease epidemiology, the genetics of host-pathogen interaction and the management of BHB on oat, barley and corn.

plant biology↗

bioRxiv2024

Barley variety Quest exhibits broad-spectrum, moderate quantitative resistance against diverse Xanthomonas translucens pathovar translucens

Barley (Hordeum vulgare subspp. vulgare) is the fourth most widely produced cereal today and is valuable for both animal and human consumption. Bacterial leaf streak (BLS) of barley is caused primarily by X. translucens pv. translucens (Xtt) and can lead to significant yield losses. There are currently no available control methods for BLS pathogens, but there are ongoing efforts to identify and characterize sources of resistance to Xtt in available barley germplasm. These screening projects require field trials which are time-consuming and challenged due to variables introduced by environmental and weather conditions, field conditions and other organisms that may be present. Reliable greenhouse phenotyping techniques are needed to accelerate screening of barley germplasm against more Xtt strains. In this study, we established a rapid greenhouse spray inoculation protocol for pathogen-plant phenotyping. This provides a framework for rapid germplasm screening before time-consuming and limited field nursery trials. Our method confirmed the moderate quantitative resistance phenotype discovered in field trials for the cultivars Quest and Tradition against the Xtt strain CIX95. One week old seedlings of the previously characterized resistant line PI329000 were not resistant relative to the susceptible check line MW14-5371-013. The cultivar Quest then demonstrated moderate quantitative resistance against a diverse panel of Xtt strains. Xtt subgroup did not influence BLS outcomes on tested barley lines. We found evidence to support the hypothesis that the virulence of modern strains is increasing, though this does not improve their ability to cause disease on Quest.

microbiology↗

bioRxiv2024

rpfF is not required for X. translucens pv. undulosa pathogenesis

Bacterial cells self-coordinate via a mechanism called quorum sensing. In Xanthomonas species the gene rpfF encodes the quorum sensing autoinducer synthase. Xanthomonas species are divided into two main phylogenetic groups called Clade I and Clade II. The rpf quorum sensing system has been well studied in multiple Clade II Xanthomonas species and deletion of rpfF resulted in a major loss of virulence on susceptible hosts. However, the only Clade I Xanthomonas species in which the rpfF system was previously studied was in the sugarcane pathogen X. albilineans. In X. albilineans the rpf cluster plays a relatively small role in pathogenesis. Xanthomonas translucens pv. undulosa (Xtu) is a Clade I Xanthomonas species that causes bacterial leaf streak (BLS) and black chaff of wheat and barley and has increased as a concern in recent decades. Neither major resistance nor chemical treatments are available to prevent disease caused by Xtu. Interference with rpf bacterial quorum sensing systems has demonstrated some success in other systems. It was unknown whether BLS caused by Xtu could be prevented via quorum sensing interference. We found that Xtu encodes an rpfF homolog and we created an rpfF knockout mutant to study the role of the rpf system in Xtu. We found that the rpfF mutant was unaffected in its pathogenesis as it caused BLS symptoms and multiplied within wheat plants to the same levels as the wildtype strain. The Xtu rpfF mutant grew normally in lag and log phases in vitro, however it exhibited a shorter stationary phase and an early death phase in plant-derived media. The importance of RpfF in Xtus life cycle is unknown, though it appears to carry out a role in population stability. Our research determined that rpfF is not a major Xtu pathogenicity factor. Therefore, we do not recommend the targeting of the rpf quorum sensing system as a preventative treatment for BLS of wheat.

molecular biology↗

bioRxiv2023

A Ralstonia solanacearum type III effector alters the actin and microtubule cytoskeleton to promote bacterial virulence in plants

Cellular responses to biotic stress frequently involve signaling pathways that are conserved across eukaryotes. These pathways include the cytoskeleton, a proteinaceous network that senses external cues at the cell surface and signals to interior cellular components. During biotic stress, dynamic cytoskeletal rearrangements serve as a platform from which early immune-associated processes are organized and activated. Bacterial pathogens of plants and animals use proteins called type III effectors (T3Es) to interfere with host immune signaling, thereby promoting virulence. We previously found that RipU, a T3E from the soilborne phytobacterial pathogen Ralstonia solanacearum K60 (Rs K60), co-localizes with the plant cytoskeleton. Here, we show that RipU from Rs K60 (RipUK60) physically associates with both actin and tubulin and disrupts actin and microtubule cytoskeleton organization. We find that pharmacological disruption of the tomato (Solanum lycopersicum) cytoskeleton promotes Rs K60 colonization. RipUK60 suppresses cell surface-triggered immune responses including flg22-mediated reactive oxygen species (ROS) production and callose deposition. Importantly, tomato plants inoculated with Rs K60 lacking RipUK60 ({Delta}ripUK60) had reduced wilting symptoms and significantly reduced root colonization when compared to plants inoculated with wild-type Rs K60. Collectively, our data suggest that Rs K60 uses the type III effector RipUK60 to remodel cytoskeletal organization, thereby promoting pathogen virulence.

plant biology↗

bioRxiv2022

Development of genome-driven, lifestyle-informed primers for identification of the cereal infecting pathogens Xanthomonas translucens pathovars undulosa and translucens.

Bacterial leaf streak, blight and black chaff caused by Xanthomonas translucens pathovars are major diseases affecting small grains. Xanthomonas translucens pv. translucens and X. translucens pv. undulosa are seedborne pathogens that cause similar symptoms on barley, but only X. translucens pv. undulosa causes bacterial leaf streak of wheat. Recent outbreaks of X. translucens have been a concern for wheat and barley growers in the Northern Great Plains and Upper Midwest; however, there are limited diagnostic tools for pathovar differentiation. We developed a multiplex PCR based on whole-genome differences to distinguish X. translucens pv. translucens and X. translucens pv. undulosa. We validated the primers across different Xanthomonas and non-Xanthomonas strains. To our knowledge, these are the first multiplex PCR to distinguish X. translucens pv. translucens and X. translucens pv. undulosa. These molecular tools will support disease management strategies enabling detection and pathovar incidence analysis of X. translucens.

microbiology↗

bioRxiv2020

Repeated gain and loss of a single gene modulates the evolution of vascular pathogen lifestyles

Vascular pathogens travel long distances through host veins leading to life-threatening, systemic infections. In contrast, non-vascular pathogens remain restricted to infection sites, triggering localized symptom development. The contrasting features of vascular and non-vascular diseases suggest distinct etiologies, but the basis for each remains unclear. Here, we show that the hydrolase CbsA acts as a phenotypic switch between vascular and non-vascular plant pathogenesis. cbsA was enriched in genomes of vascular phytopathogenic bacteria in the Xanthomonadaceae family and absent in most non-vascular species. CbsA expression allowed non-vascular Xanthomonas to cause vascular blight while cbsA mutagenesis resulted in reduction of vascular or enhanced non-vascular symptom development. Phylogenetic hypothesis testing further revealed that cbsA was lost in multiple non-vascular lineages and more recently gained by some vascular subgroups, suggesting that vascular pathogenesis is ancestral. Our results overall demonstrate how the gain and loss of single loci can facilitate the evolution of complex ecological traits.

microbiology↗