Expression and Role of Response Regulating, Biosynthetic and Degrading Genes for Cytokinin Signaling during Clubroot Disease Development

Abstract

The obligate biotroph <i>Plasmodiophora brassicae</i> causes clubroot disease in oilseeds and vegetables of the Brassicaceae family, and cytokinins play a vital role in clubroot formation. In this study, we examined the expression patterns of 17 cytokinin-related genes involved in the biosynthesis, signaling, and degradation in Chinese cabbage inoculated with the Korean pathotype group 4 isolate of <i>P. brassicae</i>, Seosan. This isolate produced the most severe clubroot symptoms in Chinese cabbage cultivar "Bullam-3-ho" compared to three other Korean geographical isolates investigated. <i>BrIPT1</i>, a cytokinin biosynthesis gene, was induced on Day 1 and Day 28 in infected root tissues and the upregulation of this biosynthetic gene coincided with the higher expression of the response regulators <i>BrRR1</i>, on both Days and <i>BrRR6</i> on Day 1 and 3. <i>BrRR3</i> and <i>4</i> genes were also induced during gall enlargement on Day 35 in leaf tissues. The <i>BrRR4</i> gene, which positively interact with phytochrome B, was consistently induced in leaf tissues on Day 1, 3, and 14 in the inoculated plants. The cytokinin degrading gene <i>BrCKX3-6</i> were induced on Day 14, before gall initiation. <i>BrCKX2,3,6</i> were induced until Day 28 and their expression was downregulated on Day 35. This insight improves our current understanding of the role of cytokinin signaling genes in clubroot disease development.