Unveiling the Potential Role of Dhurrin in Sorghum During Infection by the Head Smut Pathogen Sporisorium reilianum f. sp. reilianum

Authors: FALL, COUMBA - Texas A&M University; LIM, SEUNGHYUN - Orise Fellow; Ahn, Ezekiel; Park, Sunchung; Prom, Louis; MAGILL, CLINT - Texas A&M University

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2025
Publication Date: 2/28/2025
Citation: Fall, C., Lim, S., Ahn, E.J., Park, S., Prom, L.K., Magill, C. 2025. Unveiling the Potential Role of Dhurrin in Sorghum During Infection by the Head Smut Pathogen Sporisorium reilianum f. sp. reilianum. Plants. 14(5):740. https://doi.org/10.3390/plants14050740.
DOI: https://doi.org/10.3390/plants14050740

Interpretive Summary: Sorghum is a vital cereal crop, especially in regions with limited water, and it contains a compound called dhurrin. Dhurrin can release hydrogen cyanide (HCN), which is thought to help defend the plant against pests and diseases. This study focused on understanding how dhurrin might be involved in protecting sorghum from a disease called head smut, caused by the fungus Sporisorium reilianum f. sp. reilianum (SRS). We measured the potential of sorghum plants to release HCN and found that it was linked to how long it took for disease symptoms to appear after infection with SRS. Plants with higher HCN potential seemed to take longer to show symptoms. We also looked at the activity of genes involved in making dhurrin in a head smut-resistant and a susceptible sorghum variety after infecting them with SRS. In the resistant variety, these genes became more active, particularly one gene called UGT85B1, suggesting that dhurrin production might be ramped up as a defense mechanism. Using genome-wide association studies (GWAS), we searched for genetic markers associated with HCN potential and found some links to genes involved in plant defense, but these were not directly near the genes known to be involved in dhurrin production or breakdown. This research suggests that dhurrin plays a role in sorghum's defense against head smut, and that resistant plants might boost dhurrin production when infected. Understanding this relationship could help breeders develop sorghum varieties with enhanced resistance to head smut, contributing to more stable and secure food production, especially in areas where this disease is a major problem. It provides valuable insights for sorghum breeders, farmers, and plant scientists.

Technical Abstract: This study investigated the potential role of the cyanogenic glucoside dhurrin in sorghum's response to the head smut pathogen Sporisorium reilianum f. sp. reilianum (SRS). We examined the relationship between hydrogen cyanide potential (HCNp), seed morphology traits, and disease response using correlation analysis, hierarchical clustering, and principal component analysis in two sorghum collections (C1 and C2) comprising Senegalese and Nigerien accessions. A strong positive correlation (r = 0.88, p = 0.0001) was observed between average HCNp scores and the latency period of SRS infection in seedlings. Quantitative RT-PCR analysis revealed upregulation of dhurrin biosynthetic genes (CYP79A1, CYP71E1, and UGT85B1) in the SRS-resistant sorghum line BTx635 following inoculation, with UGT85B1 showing the most pronounced increase at 48 hours post-inoculation. In contrast, these genes showed minimal expression in the susceptible line BTx643. Genome-wide association studies (GWAS) using HCNp scores identified significant SNPs (p < 0.0001) on chromosomes 1, 4, and 8, where dhurrin biosynthetic and catabolic genes are located, although these SNPs were not in close proximity to these genes. Several significant SNPs were located in regions associated with plant defense, including genes encoding proteins with zinc-finger domains and a TIP120 homolog. These results suggest that dhurrin may contribute to sorghum's defense against SRS infection, potentially through the release of HCN. The observed upregulation of dhurrin biosynthetic genes in the resistant line supports this hypothesis. Further investigation into the expression of dhurrin catabolic genes and the precise role of HCN in this interaction is warranted. This study provides valuable insights for developing head smut-resistant sorghum varieties and highlights the complex interplay between cyanogenic glucosides and pathogen defense in plants.