Brassica-Specific Orphan Gene CROG1 Confers Clubroot Resistance in Arabidopsis via Phenylpropanoid Pathway Activation

Clubroot disease, caused by Plasmodiophora brassicae, poses a serious threat to global Brassica crop production. Orphan genes (OGs), which are species or lineage-specific and lack detectable homologs in other taxa, have been implicated in various biotic stress responses. Here, we identified a novel Brassica rapa-specific orphan gene, designated CROG1, that confers resistance to clubroot. Heterologous overexpression of CROG1 in Arabidopsis thaliana significantly enhanced resistance to P. brassicae. Transcriptomic profiling of CROG1-overexpressing lines highlighted the essential role of the phenylpropanoid biosynthesis pathway, showing upregulation of key lignin synthesis genes (including CCoAMT, CAD6, PER4, and AZI1) and defense-related regulators (RBOHC and WAKs). Weighted co-expression network analysis further corroborated the link between CROG1-mediated resistance and enhanced lignin deposition and cell wall reinforcement. Our findings establish CROG1 as a Brassica-specific orphan gene that enhances clubroot resistance via phenylpropanoid pathway activation. These results highlight the potential of orphan genes as novel genetic resources for breeding clubroot-resistant Brassica varieties, offering a sustainable strategy to mitigate yield losses caused by this devastating disease.