Transcriptome analysis of resistant and susceptible M. truncatula genotypes in response to the necrotrophic fungus A. medicaginicola

Authors: BOTKIN, JACOB - University Of Minnesota; Curtin, Shaun

Submitted to: BMC Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Fungal pathogens cause significant economic losses in agroecosystems globally. The necrotrophic fungus, Ascochyta medicaginicola, is the causal agent of spring black stem (SBS) and leaf spot disease of alfalfa (Medicago sativa), a nutrient-rich source of forage for livestock. This disease also affects the alfalfa relative barrel medic (Medicago truncatula), a model legume with expansive genomic resources. Previous studies have indicated that plant hormones and antimicrobial compounds are involved in the host response, however specific genetic factors that enable host resistance to this destructive pathogen remain unresolved. We conducted a comparative gene expression study for a resistant and susceptible accession of barrel medic subjected to pathogen infection. We investigated genes that were uniquely expressed in the resistant accession in response to the pathogen, and identified candidate genes for disease resistance. Overall, this research further elucidates the legume immune system in response to necrotrophic fungi. Future research will leverage gene-editing technologies to functionally validate candidate genes for disease resistance.

Technical Abstract: Ascochyta blights cause yield losses in all major legume crops. Spring black stem (SBS) and leaf spot disease is a major foliar disease of M. truncatula and M. sativa (alfalfa) caused by necrotrophic fungus Ascochyta medicaginicola. This present study sought to identify candidate genes for SBS disease resistance for future functional validation. We employed RNA-Seq to profile the transcriptomes of a resistant (HM078) and susceptible (A17) genotype of M. truncatula at 24, 48, and 72 hours post inoculation. Preliminary microscopic examination showed reduced pathogen growth on the resistant genotype. In total, 192 and 2,908 differentially expressed genes (DEGs) were observed in the resistant and susceptible genotype, respectively. Functional enrichment analysis revealed the susceptible genotype engaged in processes in the cell periphery and plasma membrane, as well as flavonoid biosynthesis whereas the resistant genotype utilized calcium ion binding, cell wall modifications, and external encapsulating structures. Candidate genes for disease resistance were selected based on criteria, such as dramatic upregulation or upregulation over time in the resistant genotype, contrasting expression profiles in QTL, hormone pathway genes, plant disease resistance genes, and receptor-like kinases. Overall, fifteen promising candidate genes for SBS disease resistance were identified. These genes will be sources for future targeted mutagenesis and candidate gene validation potentially helping to improve disease resistance to this devastating foliar pathogen.