AUTHOR=Hossain Md Musharaf , Pérez-López Edel , Todd Christopher D. , Wei Yangdou , Bonham-Smith Peta C. 

TITLE=Endomembrane-Targeting Plasmodiophora brassicae Effectors Modulate PAMP Triggered Immune Responses in Plants

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.651279

DOI=10.3389/fmicb.2021.651279

ISSN=1664-302X

ABSTRACT=<p><italic>Plasmodiophora brassicae</italic> is a devastating obligate, intracellular, biotrophic pathogen that causes clubroot disease in crucifer plants. Disease progression is regulated by effector proteins secreted by <italic>P. brassicae</italic>. Twelve <italic>P. brassicae</italic> putative effectors (<italic>Pb</italic>PEs), expressed at various stages of disease development [0, 2, 5, 7, 14, 21, and 28 days post inoculation (DPI)] in Arabidopsis and localizing to the plant endomembrane system, were studied for their roles in pathogenesis. Of the 12 <italic>Pb</italic>PEs, seven showed an inhibitory effect on programmed cell death (PCD) as triggered by the PCD inducers, <italic>PiINF1</italic> (<italic>Phytophthora infestans</italic> Infestin 1) and <italic>PiNPP1</italic> (<italic>P. infestans</italic> necrosis causing protein). Showing the strongest level of PCD suppression, <italic>PbPE15</italic>, a member of the 2-oxoglutarate (2OG) and Fe (II)-dependent oxygenase superfamily and with gene expression during later stages of infection, appears to have a role in tumorigenesis as well as defense signaling in plants. <italic>PbPE13</italic> produced an enhanced <italic>PiINF1</italic>-induced PCD response. Transient expression, in <italic>Nicotiana benthamiana</italic> leaves of these <italic>Pb</italic>PEs minus the signal peptide (SP) (<sup>Δ<italic>sp</italic></sup><italic>Pb</italic>PEGFPs), showed localization to the endomembrane system, targeting the endoplasmic reticulum (ER), Golgi bodies and nucleo-cytoplasm, suggesting roles in manipulating plant cell secretion and vesicle trafficking. <sup>Δ<italic>sp</italic></sup><italic>Pb</italic>PE13GFP localized to plasma membrane (PM) lipid rafts with an association to plasmodesmata, suggesting a role at the cell-to-cell communication junction. Membrane relocalization of <sup>Δ<italic>sp</italic></sup><italic>Pb</italic>PE13GFP, triggered by flagellin N-terminus of <italic>Pseudomonas aeruginosa</italic> (flg22 – known to elicit a PAMP triggered immune response in plants), supports its involvement in raft-mediated immune signaling. This study is an important step in deciphering <italic>P. brassicae</italic> effector roles in the disruption of plant immunity to clubroot disease.</p>