Comparing the infection biology and gene expression differences of Plasmodiophora brassicae primary and secondary zoospores

Abstract

Plasmodiophora brassicae (Wor.) is an obligate plant pathogen affecting Brassicae worldwide. To date, there is very little information available on the biology and molecular basis of P. brassicae primary and secondary zoospore infections. To examine their roles, we used microscope to systematically investigate the infection differences of P. brassicae between samples inoculated separately with resting spores and secondary zoospores. The obvious development of P. brassicae asynchrony that is characterized by secondary plasmodium, resting sporangial plasmodium, and resting spores was observed at 12 days in Brassica rapa inoculated with resting spores but not when inoculated with secondary zoospores at the same time. Inoculation with resting spores resulted in much more development of zoosporangia clusters than inoculation with secondary zoospores in non-host Spinacia oleracea. The results indicated that primary zoospore infection played an important role in the subsequent development. To improve our understanding of the infection mechanisms, RNA-seq analysis was performed. Among 18 effectors identified in P. brassicae, 13 effectors were induced in B. rapa seedlings inoculated with resting spores, which suggested that the pathogen and host first contacted, and more effectors were needed. Corresponding to those in B. rapa, the expression levels of most genes involved in the calcium-mediated signaling pathway and PTI pathway were higher in plants inoculated with resting spores than in those inoculated with secondary zoospores. The ETI pathway was suppressed after inoculation with secondary zoospores. The genes induced after inoculation with resting spores were suppressed in B. rapa seedlings inoculated with secondary zoospores, which might be important to allow a fully compatible interaction and contribute to a susceptible reaction in the host at the subsequent infection stage. The primary zoospores undertook an more important interaction with plants.

Local endoreduplication of the host is a conserved process during Phytomyxea-host interaction

“…Endoreduplication is a universal, and constant process during the Phytomyxid life cycle Phytomyxea have two functionally different types of plasmodia: the sporangial (primary) plasmodia are formed during the initial phase of infection and can be found in the main host but also in alternative hosts (Neuhauser et al, 2014;Yang et al, 2022). Sporogenic (secondary) plasmodia, which develop into persistent resting spores and induce large hypertrophied cell clusters, are only found in the main host (Neuhauser et al, 2011a).…”

ThePlasmodiophora brassicaeeffector PbEGF1 manipulates plant immunity and regulate primary infection

“…Host-induced gene silencing (HIGS) is an advancement of the virus induced gene silencing (VIGS) technique. If host cells have dsRNA that is homologous to the pathogen's sequence, it has the potential to induce gene silencing of the corresponding target (Panwar et al, 2018;Chen et al, 2022). Here, a recombinant vector containing a hairpin sequence of PbEGF1 was transiently expressed in B. napus via Agrobacterium-mediated.…”

“…The secretory activity of certain putative effectors in P. brassicae has been experimentally validated (Schwelm et al,3 2015; Rolfe et al, 2016;Chen et al, 2019;Pérez-López et al, 2020). Recent studies have also identified specific effectors during the early and late stage of infection, as well as differentially expressed effectors associated with primary and secondary infection (Chen et al, 2019;Pérez-López et al, 2020;Yang et al, 2022). Effector secretion serves as a strategy employed by pathogens to interfere with host growth processes.…”