Actin-related defense mechanism to reject penetration attempt by a non-pathogen is maintained in tobacco BY-2 cells.
The actin cytoskeleton is a key player in defense responses during early stages of infection by fungal pathogens. To investigate molecular mechanisms of actin-related defense responses, a cultured tobacco ( Nicotiana tabacum L.) BY-2 cell system was devised. When conidia were directly deposited on BY-2 cells, neither a pathogen, Erysiphe cichoracearum, nor a non-pathogen, Erysiphe pisi, was able to form appressoria or haustoria on BY-2 cells. On the other hand, conidia of the powdery mildews formed appressoria on BY-2 cells if they were covered with a thin hydrophobic membrane of Formvar. Percentages of appressoria formation of the powdery mildews on the Formvar-covered BY-2 cells were mostly the same as those on leaf epidermal cells. The pathogen successfully penetrated through the membrane into BY-2 cells and formed haustoria, whereas penetration attempts of the non-pathogen were completely rejected by the BY-2 cells similar to attempts on leaf epidermal cells. On the other hand, when BY-2 cells were treated with actin cytoskeleton-depolymerizing agents, cytochalasins, the non-pathogen became able to penetrate and form haustoria in BY-2 cells. Simultaneously, cytochalasin inhibited callose deposition at penetration sites of the non-pathogen. These results demonstrated that the actin cytoskeleton plays an important role in defense mechanisms against fungal penetration, even in the dedifferentiated cultured cells. The newly devised Formvar-covered cultured cell system will be a useful tool for molecular dissection of signal perception and defense mechanisms of plant cells during the early stage of fungal attack.
Kobayashi
Issei
I
Laboratory of Plant Infection, Faculty of Bioresources, Mie University, 514-8507, Tsu, Japan. issei@bio.mie-u.ac.jp
Hakuno
Humiaki
H
D000199:Actins / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D005658:Fungi / Q000472:pathogenicity / Q000502:physiology*; D007113:Immunity, Innate; D010935:Plant Diseases / Q000382:microbiology; D011145:Polyvinyls / Q000494:pharmacology; D013045:Species Specificity; D014026:Nicotiana / Q000166:cytology / Q000187:drug effects / Q000382:microbiology* / Q000502:physiology*
D000199:Actins; D011145:Polyvinyls; C013215:polyvinyl acetate