Exploring the hidden tripartite association between bacterial endosymbionts, plant parasitic nematodes, and plants

Abstract1 - Bioinformatic sequence data mining can yield hidden microbial symbionts that might normally be filtered and removed as contaminants. Wolbachia is a widespread bacterial endosymbiont in insects and filarial nematodes, but its distribution in plant-parasitic nematodes (PPNs) remains underexplored. To date, Wolbachia has only been reported in the PPNs Radopholus similis, Radopholus arabocoffeae, Pratylenchus penetrans, and a fourth nematode, yet nematode-infecting Wolbachia may have been widespread early in the evolutionary history of the phylum based on evidence of horizontal gene transfers, suggesting there may be undiscovered Wolbachia infections in PPNs. The goal of this study was to more broadly sample PPN Wolbachia strains to enable further comparative genomic analyses that may reveal Wolbachia's role and identify targets for biocontrol. We assessed field-sampled nematode communities to search for this endosymbiont across tylenchid nematodes using genome sequencing, assembly, and phylogenetic analysis. We showed some sequences were similar to gene regions in a published Heterodera schachtii (sugarbeet nematode) draft genome. Detailed analyses comparing read coverage, GC content, pseudogenes, and phylogenomic patterns, clearly demonstrated that the H. schachtii Wolbachia-like sequence was not only a novel Wolbachia strain (hereafter, denoted wHet) but also a complete, circular genome The MrBayes phylogeny tree construction has shown wHet close to another PPN Wolbachia, wTex, Also, the pseudogenes in wHet has shown its relatedness to PPN clade, and no significant enriched GO terms were observed when compared to PPN clade. Among two published whole genome shotgun assemblies for H. schachtii, one from the Netherlands and one from Germany, only the Netherlands assembly included the novel wHet Wolbachia. We speculate that the German H. schachtii assembly may have removed bacteria during bioinformatic steps that removed bacterial contamination. Other available Heterodera species were also analyzed for the presence of wHet. Future analyses will focus on comparative pathway analysis between PPN Wolbachia strains and microscopic localization of wHet in sugarbeet nematode populations. Abstract2 - Management of root-lesion nematodes (Pratylenchus penetrans) poses a significant challenge. To help protect against P. penetrans, various cover crops such as carrots, oats, onion, radish, and marigold have been tested, but their beneficial effects were short-term. As an alternative strategy, this study investigated the anti-nematode effects of sorghum. Sorghum as green manure was shown to be effective in protecting against root-knot nematodes. Such benefits may be due to compounds released from plant roots. Some root exudates facilitate infection and damage by plant parasitic nematodes, whereas others reduce this damage. The compound sorgoleone is a well-studied exudate from sorghum root hair which is known to suppress the growth of plants in the surrounding area due to its allelopathic properties. A wide range of bacterial taxa across the rhizosphere are known to be either inhibited or promoted by sorgoleone. Our analysis focused on evaluating the effects of sorgoleone on P. penetrans. We extracted sorgoleone from Sorghum bicolor roots and exposed field-sampled populations of P. penetrans to this compound. Total RNA was extracted to analyze the changes in gene expression in response to sorgoleone exposure. Differential gene expression was calculated using DeSeq2. In the future, combining analyses of gene expression changes and behavioral changes in P. penetrans in response to sorgoleone may help clarify the mechanism of sorghum effectiveness as a cover crop and provide potential avenues for breeding enhanced sorgoleone-secreting varieties of crops.

Embargo status: Restricted until 09/2028. To request the author grant access, click on the PDF link to the left.