Biology subjects

Mitchum, M. G.

Publications and source records attributed to Mitchum, M. G..

5 recordsLinked to original sources

bioRxiv2026

Conservation of Nuclear Receptor DAF-12 with Evidence for Ligand Diversification in Plant-Parasitic Nematodes

Plant-parasitic nematodes cause extensive crop losses that threaten global food security and create substantial economic hardship, yet strategies for their control remain limited. Although plant-parasitic nematodes have life cycles that mirror those of their free-living and animal-parasitic relatives, comparatively little is known about the signals that drive life-cycle progression. Dafachronic acids (DAs) are steroid hormones that control life cycle by activating DAF-12 nuclear receptors in Caenorhabditis elegans and animal-parasitic nematodes. To define whether an analogous pathway exists in plant-parasitic nematodes, we investigated the responsiveness of DAF-12 orthologs from six plant-parasitic nematode species to {Delta}7-DA, an endogenous DAF-12 ligand in C. elegans and several animal-parasitic nematodes. We find that whereas some plant-parasitic nematode receptors are activated by {Delta}7-DA, others are not. Structural modeling of all six ligand-binding domains, together with docking of {Delta}7-DA into each model, indicates that responsiveness is governed by a combinatorial ligand-recognition network surrounding the ligand carboxylate rather than by any single contact residue. We further demonstrate that egg and second-stage juvenile extracts from the soybean cyst nematode, Heterodera glycines, lack detectable DA but contain distinct lipophilic fractions that activate its DAF-12 ortholog. Together, these findings suggest that many plant-parasitic nematodes utilize endogenous DAF-12 ligands that are structurally distinct from DA. Uncovering modulators of this pathway could lead to new strategies to combat nematode-driven crop loss.

molecular biology↗

bioRxiv2025

Single-cell multi-omic characterization of the soybean root response to cyst nematode infection

Soybean cyst nematodes parasitize soybean roots by inducing the formation of multinucleate syncytia to feed and complete their life cycle. However, the molecular basis of syncytia initiation and development remains limited. Here, we generated an integrated single-nucleus RNA and chromatin accessibility profile of soybean roots from infected and uninfected plants. We profiled 56,448 high-quality nuclei and identified all major root cell types, including distinct subpopulations enriched with syncytial nuclei. Transcriptomic and chromatin accessibility analyses support their procambium cell signature that progresses through distinct stages associated with immune suppression, cell fusion, and endoreduplication. Integrative gene expression and transcription factor motif chromatin accessibility analyses identified CAMTA1, as a potential transcriptional repressor of defense-related genes including receptor-like kinases, whereas MYB, MYB-related, and E2F were identified as potential transcriptional activators that coordinate cell wall remodeling, chromatin modification and DNA replication, respectively, across developmental trajectories. These findings provide mechanistic insights into host reprogramming during nematode parasitism and serve as a foundational resource for engineering nematode-resistant soybean.

plant biology↗

bioRxiv2024

Evaluation of Inducible Gene Expression Systems for Beet Cyst Nematode Infection Assays in Arabidopsis thaliana

Cyst nematodes co-opt plant developmental programs for the establishment of a permanent feeding site called a syncytium in plant roots. In recent years, the role of plant developmental genes in syncytium formation has gained much attention. One main obstacle in studying the function of development-related genes in syncytium formation is that mutation or ectopic expression of such genes can cause pleiotropic phenotypes making it difficult to interpret nematode-related phenotypes, or in some cases, impossible to carry out infection assays due to aberrant root development. Here, we tested three commonly used inducible gene expression systems for their application in beet cyst nematode infection assays of the model plant Arabidopsis thaliana. We found that even a low amount of ethanol diminished nematode development, deeming the ethanol-based system unsuitable for use in cyst nematode infection assays; whereas treatment with estradiol or dexamethasone did not negatively affect cyst nematode viability. Dose and time course responses showed that in both systems, a relatively low dose of inducer (1 M) is sufficient to induce high transgene expression within 24 hours of treatment. Transgene expression peaked at 3-5 days post induction and began to decline thereafter, providing a perfect window for inducible transgenes to interfere with syncytium establishment while minimizing any adverse effects on root development. These results indicate that both estradiol- and dexamethasone-based inducible gene expression systems are suitable for cyst nematode infection assays. The employment of such systems provides a powerful tool to investigate the function of development essential plant genes in syncytium formation.

plant biology↗

bioRxiv2024

A Major Role of Class III HD-ZIPs in Promoting Sugar Beet Cyst Nematode Syncytium Formation in Arabidopsis

Cyst nematodes use a stylet to secrete plant CLE-like peptide effector mimics into selected root cells of their host plants to hijack CLE signaling pathways for feeding site (syncytium) formation. Here, we identified ATHB8, a HD-ZIP III family transcription factor, as a downstream component of the CLE signaling pathway in syncytium formation. ATHB8 is expressed in the early stages of syncytium initiation, and then transitions to neighboring cells of the syncytium as it expands; an expression pattern coincident with auxin response at the infection site. Conversely, MIR165a, which expresses in endodermal cells and moves into the vasculature to suppress HD-ZIP III TFs, is down-regulated near the infection site. Knocking down HD-ZIP III TFs by inducible over-expression of MIR165a in Arabidopsis dramatically reduced female development of the sugar beet cyst nematode (Heterodera schachtii). HD-ZIP III TFs are known to function downstream of auxin to promote cellular quiescence and define stem cell organizer cells in vascular patterning. Taken together, our results suggest that HD-ZIP III TFs may function as a connecting point for CLE and auxin signaling pathways in promoting syncytium formation, possibly by inducing root cells into a quiescent status and priming them for initial syncytial cell establishment and/or subsequent cellular incorporation.

plant biology↗

bioRxiv2018

The genome of the soybean cyst nematode (Heterodera glycines) reveals complex patterns of duplications involved in the evolution of parasitism genes

Heterodera glycines, commonly referred to as the soybean cyst nematode (SCN), is an obligatory and sedentary plant parasite that causes over a billion-dollar yield loss to soybean production annually. Although there are genetic determinants that render soybean plants resistant to certain nematode genotypes, resistant soybean cultivars are increasingly ineffective because their multi-year usage has selected for virulent H. glycines populations. The parasitic success of H. glycines relies on the comprehensive re-engineering of an infection site into a syncytium, as well as the long-term suppression of host defense to ensure syncytial viability. At the forefront of these complex molecular interactions are effectors, the proteins secreted by H. glycines into host root tissues. The mechanisms of effector acquisition, diversification, and selection need to be understood before effective control strategies can be developed, but the lack of an annotated genome has been a major roadblock. Here, we use PacBio long-read technology to assemble a H. glycines genome of 738 contigs into 123Mb with annotations for 29,769 genes. The genome contains significant numbers of repeats (34%), tandem duplicates (18.7Mb), and horizontal gene transfer events (151 genes). Using previously published effector sequences, the newly generated H. glycines genome, and comparisons to other nematode genomes, we investigate the evolutionary mechanisms responsible for the emergence and diversification of effector genes.

genomics↗