Verticillium dahliae Kleb. is a soil-borne fungal pathogen that causes wilt disease in a wide range of crops, including cotton, and causes serious loss of lint in China. Infection of cotton roots by V. dahliae in soil leads to the colonization of vascular tissues in host plants. However, the development of specialized infection structures to overcome plant barriers during root infection by V. dahliae has been controversial. Moreover, the molecular features and regulation mechanism in infection process ofV. dahliae remain elusive.

Dr. Guo Huishan’s group in the State Key Laboratory of Plant Genomics, Institute of Microbiology of Chinese Academy of Sciences, provides for the first time the molecular features for accurate identification of hyphopodium, an infectious structure in V. dahliae. They found that the VdPls1, a tetraspanin, and the VdNoxB, a catalytic subunit of membrane-bound NADPH oxidases for reactive oxygen species (ROS) production, were specifically expressed in hyphopodia. VdPls1 and VdNoxB highly co-localize with the plasma membrane at the base of hyphopodia, where ROS and penetration pegs are generated. The strain with deletion of VdPls1 or VdNoxB  developed defective hyphpodia incapable of producing ROS and penetration pegs. Moreover, they found that VdPls1/VdNoxB-mediated ROS production elevates tip-high cytoplasmic free calcium ions (Ca²⁺) in hyphopodia to activate conservation calcineurin-Crz1 signaling for the establishment polarized penetration peg formation. Together with the loss of virulence when VdPls1 or VdNoxB was deleted, their data demonstrate that VdNoxB/VdPls1-mediated ROS production activates VdCrz1 signaling through Ca²⁺ elevation in hyphopodia, infectious structures of V. dahliae, to regulate penetration peg formation during the initial colonization of cotton roots.