Biology subjects

Fitzpatrick, C. R.

Publications and source records attributed to Fitzpatrick, C. R..

4 recordsLinked to original sources

bioRxiv2025

Recognition of unique cell surface glycopolymers by diversified lectin domains specifies umbrella toxin targeting

The bacterial cell envelope provides structural integrity and is an essential conduit through which the organism interacts with its environment. However, the molecular structures of its constituents can also be exploited as receptors, permitting threats such as toxins and phage access to the cell. We previously demonstrated that Streptomyces coelicolor secretes an umbrella toxin particle that acts in a highly selective manner to inhibit the hyphal growth of competing Streptomyces strains. Here, we identify the receptor of umbrella toxins as teichuronic acid (TUA) oligosaccharides anchored to the cell surface through linkage to wall teichoic acids (WTA). We show that the carbohydrate portion of this previously undescribed hybrid TUA-WTA molecule is variable across species and that targeting specificity derives from its selective recognition by diversified lectin domains associated with umbrella particles. A cryo-EM structure of a lectin-TUA complex reveals the molecular basis for umbrella toxin cell targeting and, in conjunction with bioinformatic analyses, provides insights into a molecular arms race that we posit drives diversification of umbrella particles and the chemical composition of Streptomyces cell envelopes.

microbiology↗

bioRxiv2024

An efflux pump family distributed across plant commensal bacteria conditions host- and organ-specific detoxfication of a host-specific glucosinolate

In nature, plants recruit a diverse microbial community, the plant microbiome, that is distinct from the surrounding soil community 1-4. To understand the forces that shape the plant microbiome we need to characterize the microbial traits that contribute to plant colonization. We used barcoded mutant libraries to identify bacterial genes that contribute to the colonization of a monocot and a eudicot host 5-7. We show that plant colonization is influenced by dozens of genes. While some of these colonization genes were shared between the two host plant species, most were highly specific, benefiting the colonization of a single host and organ. We characterized an efflux pump that specifically contributes to Arabidopsis shoot colonization. This efflux pump is prevalent across Pseudomonadota genomes, yet benefits the bacterial association with only a small subset of Arabidopsis thaliana accessions. Leveraging genomic diversity within Arabidopsis thaliana, we confirmed that specific glucosinolate breakdown products are detoxified by this family of efflux pumps. The broad prevalence of this efflux pump family suggests that its members contribute to protection of commensal bacteria from collateral damage of plant glucosinolate-based defense responses to herbivores and necrotrophic pathogens.

microbiology↗

bioRxiv2022

Broader functions of TIR domains in Arabidopsis immunity

TIR domains are NAD-degrading enzymes that function during immune signaling in prokaryotes, plants, and animals. In plants, most TIR domains are incorporated into intracellular immune receptors. In Arabidopsis, TIR-derived small molecules bind and activate EDS1 heterodimers, which in turn activate RNLs, a class of cation channel-forming immune receptors. RNL activation drives cytoplasmic Ca2+ influx, transcriptional reprogramming, pathogen resistance and host cell death. We screened for mutants that suppress an RNL activation mimic allele and identified a TIR-containing immune receptor, SADR1. Despite functioning downstream of an auto-activated RNL, SADR1 is not required for defense signaling triggered by other tested TIR-containing immune receptors. SADR1 is required for defense signaling initiated by some trans-membrane pattern recognition receptors and contributes to the unbridled spread of cell death in lesion simulating disease 1. Together with RNLs, SADR1 regulates defense gene expression at infection site borders, likely in a non-autonomous manner. RNL mutants that cannot sustain this pattern of gene expression are unable to prevent disease spread beyond localized infection sites, suggesting that this pattern corresponds to a pathogen containment mechanism. SADR1 potentiates RNL-driven immune signaling partially through the activation of EDS1, but also partially independently of EDS1. We studied EDS1-independent TIR function using nicotinamide, an NADase inhibitor. We observed decreased defense induction from trans-membrane pattern recognition receptors and decreased calcium influx, pathogen growth restriction and host cell death following intracellular immune receptor activation. We demonstrate that TIR domains can potentiate calcium influx and defense and are thus broadly required for Arabidopsis immunity.

plant biology↗

bioRxiv2019

The bacterial microbiota of a parasitic plant and its host

How plant-associated microbiota are shaped by, and potentially contribute to the unique ecology and heterotrophic life history of parasitic plants is relatively unknown. Here, we investigate the leaf and root bacterial communities associated with the root holoparasite Orobanche hederae and its host plant Hedera spp. We sequenced the V4 region of the 16S rRNA gene from DNA extracted from leaf and root samples of naturally growing populations of Orobanche and infected and uninfected Hedera. Root bacteria inhabiting Orobanche were less diverse, had fewer co-associations, and displayed increased compositional similarity to leaf bacteria relative to Hedera. Overall, Orobanche bacteria exhibited significant congruency with Hedera root bacteria across sites, but not the surrounding soil. Infection had localized and systemic effects on Hedera bacteria, which included effects on the abundance of individual taxa and root network properties. Collectively, our results indicate that the parasitic plant microbiome is derived but distinct from host plant microbiota, exhibits increased homogenization between shoot and root tissues, and displays far fewer co-associations among individual bacterial members. Host plant infection is accompanied by modest changes of associated microbiota at both local and systemic scales compared with uninfected individuals. Our results provide insight into the assembly and function of plant microbiota.

ecology↗