Metabolomic Analysis of <em>Rlm1</em>-Based Blackleg Resistance

To elucidate the biochemical mechanisms underlying Rlm1-mediated blackleg resistance, we performed a metabolomic analysis comparing a susceptible DH line of Topas and its isogenic Rlm1-carrying resistant counterpart. Our results revealed significant differences in metabolite profiles post-inoculation. Rlm1-mediated resistance was characterized by early and sustained upregulation of lysine degradation metabolites, particularly pipecolic acid (PA), which increased up to 326-fold, highlighting its role in resistance. Salicylic acid (SA) and its derivative gentisic acid (GA) were also elevated, suggesting a coordinated hormonal defense response. Increased accumulation of glucosinolates (GLS) and γ-aminobutyric acid (GABA) likely contributed to antimicrobial defense and cell wall reinforcement. Additionally, activation of tryptophan metabolism and melatonin biosynthesis, indicated by elevated N-acetylserotonin and 5-methoxytryptamine, suggests their involvement in the defense responses. Conversely, resistant plants exhibited reduced accumulation of flavonoid and phenylpropanoid metabolites, potentially reflecting a strategic reallocation of metabolic resources. Exogenous application of PA, SA, GA and ferulic acid significantly reduced lesion sizes in susceptible canola lines, confirming their roles in defense. Moreover, treatment with piperonylic acid, a phenylpropanoid pathway inhibitor, also reduced infection, supporting the notion of metabolic shift in resistant plants. These findings provide new insights into Rlm1-mediated resistance mechanisms, complementing our prior transcriptome study of Rlm1 resistance and highlighting the role of lysine degradation, PA and SA signaling. Understanding these metabolic shifts may improve breeding strategies to enhance durable blackleg resistance in canola.