Comparative proteomic analysis of host responses to Plasmodiophora brassicae infection in susceptible and resistant Brassica oleracea

Clubroot disease, caused by Plasmodiophora brassicae, is one of the most devastating diseases affecting members of the Brassicaceae family. It is difficult to control by chemical or cultural means, and the molecular mechanisms underlying interactions with Brassica oleracea (cabbage) remain poorly understood. Herein, we used a proteomic approach to investigate B. oleracea-P. brassicae interactions during the early phases of infection in above-ground tissues. Proteins were isolated from the aerial parts of clubroot-susceptible (CT-18) and -resistant (YCR) cabbage cultivars at 5 days after inoculation with P. brassicae or buffer (mock) and resolved by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and two-dimensional gel electrophoresis. A total of 24 differentially modulated proteins were identified in at least two biological replicates, and exhibited altered expression between mock and P. brassicae treatments and/or in the different cabbage cultivars. Most of the identified proteins are involved in oxidative stress, abscisic acid (ABA) metabolism, glucose-mediated signalling and responses to stimuli. Resistant YCR plants harboured an increased abundance of ABA-responsive protein, fructose-bisphosphate aldolase and glucose sensor interaction protein compared with CT-18 plants in both mock and P. brassicae-treated samples, suggesting that they may mediate basal defences against P. brassicae infection in YCR. Specifically, we observed that susceptible (CT-18) plants expressed higher levels of cobalamin-independent methionine synthase than YCR, which may enhance susceptibility of the host. Further investigation of the identified proteins will likely facilitate the identification of key molecular determinants, potentially improving clubroot disease resistance in future cabbage crop species.