Unveiling the Molecular Basis of Stem-Physical-Strength-Mediated-Resistance (SPSMR) Mechanism Against Sclerotinia sclerotiorum in Brassicaceae: A Comparative Transcriptome Analysis of Resistant and Susceptible Genotypes

Abstract

Abstract This study elucidates the intricate molecular dynamics of the Stem-Physical-Strength-Mediated-Resistance (SPSMR) mechanism against Sclerotinia sclerotiorum in Brassicaceae. By investigating the responses of resistant and susceptible genotypes to S. sclerotiorum and their corresponding stem physical strength attributes at different infection stages, this research uncovers the molecular mechanisms underpinning resistance mediated by SPSMR. Significant differences (P ≤ 0.05) emerged between genotypes across distinct time points, with the resistant genotype displaying reduced stem lesion length, stem diameter, and stem water content, coupled with heightened stem dry matter content, stem specific density, stem breaking force, stem breaking strength, and total lignin content relative to the susceptible counterpart. Through gene expression analysis, the study unraveled unique patterns of differentially expressed genes (DEGs) linked to cell wall reinforcement, disease resistance, and pathogenesis. Upregulation of genes associated with arabinogalactan proteins, calcium ion-related proteins, xyloglucan endotransglucosylase/hydrolase, pectinesterase, expansins, S-adenosylmethionine-dependent methyltransferase, wall-associated kinases, peroxidases, laccases and phenylalanine ammonia-lyase as well as other genes associated with lignin-biosynthesis was evident in the resistant genotype. Similarly, pathogenesis-related proteins, disease resistance genes (RPS5-like, TAO1, GTP diphosphokinase), and lipoxygenases displayed substantial upregulation in the resistant genotype, while downregulation was observed in certain genes within the susceptible genotype. Additionally, gene ontology and KEGG enrichment analyses provided functional insights into DEGs. This comprehensive analysis highlights the synergy between stem physical strength and molecular components, revealing a distinctive defense strategy involving the coordinated upregulation of genes responsible for cell-wall strengthening, lignin biosynthesis, receptor kinases, pathogenesis-related and disease resistance proteins in the resistant genotype. Conversely, compromised expression patterns in the susceptible genotype underscore its challenge in mounting a robust defense. Strikingly, genes regulating intracellular pH homeostasis emerge as potential countermeasures against S. sclerotiorum virulence. Ultimately, these findings enhance our ability to develop resistant cultivars of Brassicaceae against S. sclerotiorum and similar pathogens. They offer a novel perspective on the role of stem physical strength and the intricate interplay between mechanical and molecular elements in enhancing host genetic resistance.