iTRAQ analysis of protein profile during the secondary stage of infection of Plasmodiophora brassicae in Chinese cabbage (Brassica rapa subsp. pekinensis)

High-throughput functional proteomics assay was conducted to investigate post-transcriptional changes in plant proteins upon interactions between Chinese cabbage (Brassica rapa subsp. pekinensis) and the clubroot pathogen Plasmodiophora brassicae. Protein profiles between infected and uninfected clubroot-susceptible plants of different genotypes at 10 days after inoculation (DAI) were compared and consolidated. A total of 295 proteins, functioning in energy and lipid metabolism, plant defense, cell wall modification, and hormone biosynthesis and signaling, were found to be differentially expressed during the secondary phase of the Chinese cabbage-P. brassicae interaction. It is worth noting that upregulation of proteins involved in brassinosteroids (BR) metabolism was confirmed: cycloartenol synthase (CAS1) and cytochrome P450 51G1 (CYP51G1), which are deeply involved in BR biosynthesis, were upregulated after inoculation. Furthermore, the treatment of P. brassicae-infected Chinese cabbage plants with an inhibitor of cycloartenol synthase resulted in reduced root gall size, revealing a contribution of CAS1 to clubroot development. These results demonstrated important aspects of the Chinese cabbage-P. brassicae interactions and might lead to the identification of key regulators in the BR pathway involved in clubroot development.