Transcriptome analysis of Brassica napus near-isogenic lines carrying clubroot resistance from turnip (Brassica rapa var. rapifera)

Abstract

Understanding the intricate molecular interplay between Brassica hosts and the pathogen Plasmodiophora brassicae, causative agent of clubroot disease, is pivotal for devising effective resistance to this disease in Brassica crops. While existing transcriptomic studies have elucidated the host responses to pathogen infection, a comprehensive analysis employing near-isogenic lines (NILs) remains imperative for better understanding of the resistance mechanisms. In this study, we conducted a comparative transcriptome profiling utilizing clubroot-susceptible (CS) and clubroot-resistant (CR) NILs of Brassica napus, carrying the clubroot resistance of turnip (Brassica rapa var. rapifera), at 7 and 14 days after inoculation. We observed the upregulation of the genes governing phytohormone signaling, receptor kinases, transcription factors, calcium fluxes, and glucosinolate metabolism in the CR-NILs. Notably, we identified defense-related genes associated with jasmonic acid signaling (JAZ2), calcium signaling (CNGCs, GLRs), receptor kinases (WAKs), and glucosinolate biosynthesis (APK; GSTs, also involved in ROS homeostasis) that may play pivotal roles in resistance. One of the important novel findings was the association of the JAZ2 gene with clubroot resistance in B. napus. This study also highlighted the upregulation of NLRs (RNLs and TNLs) and ERF transcription factors, offering new insights into the molecular mechanisms of clubroot resistance in B. napus. Additionally, we observed the upregulation of pathogenesis-related proteins (PR-3 and PR-4) and WRKY transcription factors (WRKY62, WRKY70), suggesting a coordinated response involving multiple layers of immunity. Based on our results, we propose a comprehensive model delineating the molecular events potentially contributing to clubroot resistance in B. napus CR-NILs. Our findings have contributed to an enhanced understanding of the potential mechanisms involved in clubroot resistance, which may have utility in targeted breeding initiatives to mitigate the threat of clubroot disease in Brassica crops including canola.

Keywords: Brassica napus; clubroot; marker-assisted breeding; near-isogenic lines; transcriptome.