Verticillium dahliae (V. dahliae) is a soil-borne, root-infecting fungal pathogen that causes severely wilt disease and leads to serious economic loss worldwide. As most of phytopathogens, V. dahliae would secrete effector proteins to evade or suppress plant immunity for successful infection of the host plants. However, the mechanism by which root-infecting fungal pathogens secrete secretory effector proteins remains unexplored.

Dr. GUO Huishan’s group at the State Key Laboratory of Plant Genomics, Institute of Microbiology of Chinese Academy of Sciences, provided for the first time the mechanism of the delivery of secretory proteins by V. dahliae during plant root infection. The paper has been published online in PLoS Pathogens. 

V. dahliae was previously found to have formed an infectious structure, hyphopodium, which develops a penetration peg to pierce plant roots. In this study, researchers observed that after penetration, the penetration peg-developed hyphal neck came into close contact with the host, forming the fungus-host penetration interface.

They observed repeated development of the hyphopodium and hyphal neck for each root cell wall penetration during V. dahliae infection, and that the cytoskeleton protein septin (VdSep5) and F-actin were organized as ring structures at the hyphal neck.

Using GFP tagging and live cell imaging, they found that several signal peptide containing secreted proteins showed ring signal accumulation/secretion at the penetration interface surrounding the septin ring, and revealed that VdSep5 plays a role in efficient secretion of secretory proteins.

Evidence that the vesicular trafficking factors VdSec22 and VdSyn8 and the exocyst subunit VdExo70 are also involved in the secretion was provided. Together with the loss/reduced of virulence when VdSep5, VdSec22, VdSyn8 or VdExo70 was deleted, the data demonstrated that the V. dahliae infection structure functions as a key signaling hub during plant infection and is the apparatus that not only breaches host cells but also provides a unique interface for the secretion of fungal effectors.

This work was supported by grants from the Strategic Priority Research Program of the Chinese Academy of Sciences and the China Transgenic Research and Commercialization Key Special Project.