Comparative Transcriptome Analysis of Rutabaga (<i>Brassica napus</i>) Cultivars Indicates Activation of Salicylic Acid and Ethylene-Mediated Defenses in Response to <i>Plasmodiophora brassicae</i>

• Main Authors: Qinqin Zhou, Leonardo Galindo-González, Victor Manolii, Sheau-Fang Hwang, Stephen E. Strelkov
• Format: Article
• Language: English
• Published: MDPI AG 2020-11-01
• Series: International Journal of Molecular Sciences
• Subjects: <i>Brassica napus</i>; <i>Plasmodiophora brassicae</i>; clubroot; RNA sequencing (RNA-seq); defense mechanisms; salicylic acid
• Online Access: https://www.mdpi.com/1422-0067/21/21/8381

Clubroot, caused by <i>Plasmodiophora brassicae</i> Woronin, is an important soilborne disease of <i>Brassica napus</i> L. and other crucifers. To improve understanding of the mechanisms of resistance and pathogenesis in the clubroot pathosystem, the rutabaga (<i>B. napus</i> subsp. <i>rapifera</i> Metzg) cultivars ‘Wilhelmsburger’ (resistant) and ‘Laurentian’ (susceptible) were inoculated with <i>P. brassicae</i> pathotype 3A and their transcriptomes were analyzed at 7, 14, and 21 days after inoculation (dai) by RNA sequencing (RNA-seq). Thousands of transcripts with significant changes in expression were identified in each host at each time-point in inoculated vs. non-inoculated plants. Molecular responses at 7 and 14 dai supported clear differences in the clubroot response mechanisms of the two genotypes. Both the resistant and the susceptible cultivars activated receptor-like protein (<i>RLP</i>) genes, resistance (<i>R</i>) genes, and genes involved in salicylic acid (SA) signaling as clubroot defense mechanisms. In addition, genes related to calcium signaling and genes encoding leucine-rich repeat (LRR) receptor kinases, the respiratory burst oxidase homolog (RBOH) protein, and transcription factors such as WRKYs, ethylene responsive factors, and basic leucine zippers (bZIPs), appeared to be upregulated in ‘Wilhelmsburger’ to restrict <i>P. brassicae</i> development. Some of these genes are essential components of molecular defenses, including ethylene (ET) signaling and the oxidative burst. Our study highlights the importance of activation of genes associated with SA- and ET-mediated responses in the resistant cultivar. A set of candidate genes showing contrasting patterns of expression between the resistant and susceptible cultivars was identified and includes potential targets for further study and validation through approaches such as gene editing.