Biology subjects

Carneal, L.

Publications and source records attributed to Carneal, L..

3 recordsLinked to original sources

bioRxiv2026

An endosymbiotic Paenibacillus sp. modulates disease severity caused by the common watermelon pathogen, Fusarium oxysporum f sp. niveum

Fungal plant pathogens can be affected by the bacteria they interact with in their environment, yet the characterization of these interactions beyond direct antagonism is lacking, especially in the case of endohyphal bacteria (EHB). Though limited in characterized examples, EHB can alter disease severity of their fungal host, providing either a potential tool or target for control. We screened isolates of Fusarium oxysporum f. sp. niveum (FON), an important soil-borne watermelon pathogen, using 16S PCR and fluorescence in situ hybridization microscopy to identify novel EHB. A symbiont of FON AS124 was identified to be a Paenibacillus sp. through genome sequencing and average nucleotide identity. To begin characterizing this relationship, we conducted watermelon infection assays using FON cured of its symbiont, the native association, and a coinoculation of fungi and bacteria. Disease severity was reduced in watermelon seedlings inoculated with the native association, though not in the coinoculation, and Paenibacillus sp. CB74 did not alone promote plant growth or inhibit fungal growth. This study shows an important functional outcome, reduced disease, for a novel symbiosis between FON and Paenibacillus sp. CB74, setting up further investigation into the mechanisms behind this outcome and the application of this interaction. ImportanceFungi pose a challenge in both the field and hospital as antifungal resistance rises and chemical control is increasingly scrutinized. In plant pathogenic fungi, endohyphal bacteria may present alternative targets or mechanisms of fungal control. These relationships are observed across diverse groups of fungi and bacteria, though few have been studied to the point of understanding impact. To contribute to the small but growing catalog of known endofungal bacterial relationships, we identified a novel symbiosis and began characterizing its functional outcomes with plant infection assays. The identified bacterial symbiont does alter disease severity of the fungal host offering a new system for both application and study of fungal pathogenesis.

microbiology↗

bioRxiv2025

Comparative genomics reveals multipartite genomes undergoing loss in the fungal endosymbiotic genus Mycetohabitans

Endosymbiotic bacteria extensively impact phenotypes of their eukaryotic hosts, while experiencing dramatic changes to their own genome as they become more host-restricted in lifestyle. Understanding the trajectory of such a genome has largely been done through study of animal-associated bacteria, especially insect endosymbionts. Yet, endofungal bacteria provide another natural experimental model for investigating how microbial genomes change when living inside of a host cell. Mycetohabitans spp. are culturable bacterial endosymbionts of the Mucoromycota fungus Rhizopus microsporus. To investigate the genome dynamics resulting from the endohyphal nature of this emerging model genus, we long-read sequenced and assembled new complete genomes to combine with previous assemblies, creating a global dataset of 28 complete Mycetohabitans genomes. All genomes were between 3.3 and 3.9 Mbp in size and were multipartite, structured into two conserved replicons with some strains having an additional plasmid. Based on evolutionary rate and gene content analysis of the different replicons, we termed the two major ones a chromosome and chromid. The differential presence of a third, mobilome-rich plasmid in some strains and the proliferation of transposable elements provide putative mechanisms for recombination or gene loss. The conservation of intact prophage and putative toxin-antitoxin systems, and extensive enrichment of secondary metabolite clusters in the Mycetohabitans genomes highlight the dynamic nature of this reducing genome. With fungal-bacterial symbioses becoming increasingly apparent phenomena, lessons learned from this symbiosis will inform our understanding of bacterial adaptation to novel hosts, and the process of microbe-microbe coevolution. SIGNIFICANCEGenomes change when organisms become closely associated, as bacterial partners undergo less opportunities for genetic exchange and become more reliant on their hosts. Our pangenome analysis of the endofungal genus Mycetohabitans shows a snapshot of evolution where the bacteria are moving from a facultative towards an obligate relationship with their host fungi. We find that Mycetohabitans genomes are marked by transposable elements, pseudogenes, a large biosynthetic repertoire, and novel bacteriophage. We provide a genomic resource to match publicly accessible strains for future work on endosymbiotic genetics and evolution.

genomics↗

bioRxiv2023

Helper NLRs Nrc2 and Nrc3 act co-dependently with Prf/Pto and activate MAPK signaling to induce immunity in tomato

Plant intracellular immune receptors, primarily nucleotide-binding, leucine-rich repeat proteins (NLRs), can detect virulence proteins (effectors) from pathogens and activate NLR-triggered immunity (NTI). Recently, sensor NLRs have been reported to function with helper NLRs to activate immune responses. We investigated the role of two helper NLRs, Nrc2 (NLR required for cell death 2) and Nrc3, on immunity in tomato to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) mediated by the sensor NLR Prf and the Pto kinase. Loss-of-function mutations in both Nrc2 and Nrc3 completely compromised Prf/Pto-mediated NTI to Pst containing the cognate effectors AvrPto and AvrPtoB. An nrc3 mutant showed intermediate susceptibility between wild-type tomato plants and a Prf mutant, while an nrc2 mutant developed only mild disease symptoms. These observations indicate that Nrc2 and Nrc3 act additively to contribute to Prf/Pto-mediated immunity. We also examined at what point Nrc2 and Nrc3 act in the Prf/Pto-mediated immune response. In the nrc2/3 mutant, programmed cell death (PCD) normally induced by constitutively-active variants of AvrPtoB, Pto or Prf was abolished, but that induced by M3K or Mkk2 was not. PCD induced by a constitutively active variant of Nrc3 was also abolished in a Nicotiana benthamiana line with reduced expression of Prf. MAPK activation triggered by expression of AvrPto in the wild-type Pto-expressing tomato plants was completely abolished in the nrc2/3 mutant. These results indicate that Nrc2 and Nrc3 act in concert with Prf/Pto and upstream of MAPK signaling. Nrc2 and Nrc3 were not required for the HR triggered by Ptr1, another sensor NLR mediating Pst resistance, although these helper NLRs do appear to be involved in resistance to certain Pst race 1 strains.

plant biology↗