Plasticity of host cell organelles in response to Pb infection

Plasmodiophora brassicae (Pb) is the most important member of the plant pathogenic protist subgroup, Rhizaria. Pb is an obligate soil-borne plant root pathogen which makes the study of Pb biology and its interaction with its host challenging. To overcome this challenge, we adopted an axenic cell culture method to study the interaction of Pb with its host plant Brassica spp. at the cellular and molecular levels. Pb, during its life cycle within the host, was confined to the cytoplasm of the infected cells. Our results showed that upon Pb infection, the dynamics of the plant cell organelles including mitochondria, plastids, nuclei, vacuoles, vesicles were altered. Both Plants and parasites diacylglycerol acyltransferases (DGAT) genes were highly expressed in the calli, which indicated a need for the oil accumulation at the switch between replication and growth stages of the pathogen. This notion was supported by the accumulation of oil bodies that were only observed inside the pathogen cells. Our results also indicated that starch was utilized by the Pb in infected cells, an indication that Pb induces cell viability by altering the host carbon metabolism. The ongoing dynamic changes in the infected plant cell organelles suggest that plant responds to Pb infection, through the induction of organellar plasticity.