Heterotrimeric G-protein and signal transduction in the nematode-trapping fungus Arthrobotrys dactyloides.
The fungus Arthrobotrys dactyloides produces specialized constricting rings to trap and then consume nematodes. The signal transduction pathway involved in the nematode-trapping process was examined. Mastoparan, an activator of G-protein, had a stimulatory effect on the inflation of ring cells, whereas a G-protein inhibitor, pertussis toxin, prevented ring-cell expansion. The 40-kDa G alpha of heterotrimeric G-proteins was specifically ADP-ribosylated by pertussis toxin. Using an antibody specific to the 35-kDa subunit G beta, we showed that immunogold-labeled G beta was more concentrated in ring cells than in the hyphae. In the absence of nematodes, the rings could be inflated by either pressurizing the culture in a syringe, raising intracellular Ca2+ concentrations, or adding warm water. We used these methods to reveal differences in responses to antagonists. The results support a model in which the pressure exerted by a nematode on the ring activates G-proteins in the ring cells. The activation leads to an increase in cytoplasmic Ca2+, activation of calmodulin, and finally the opening of water channels. The ring cells expand to constrict the ring and thus immobilize the nematode.
Chen
T H
TH
Institute of Botany, Academia Sinica, Taipei, Taiwan 11529. bochenth@ccvax.sinica.edu.tw
Hsu
C S
CS
Tsai
P J
PJ
Ho
Y F
YF
Lin
N S
NS
D020727:ADP-Ribosylation Factors; D000908:Antibodies, Fungal / Q000276:immunology; D020346:Aquaporins / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006874:Hydrostatic Pressure; D007150:Immunohistochemistry; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D008627:Mercuric Chloride / Q000037:antagonists & inhibitors; D008861:Microsomes / Q000378:metabolism; D003904:Mitosporic Fungi / Q000502:physiology*; D009355:Neomycin / Q000037:antagonists & inhibitors; D010455:Peptides; D037342:Pertussis Toxin; D015398:Signal Transduction; D010566:Virulence Factors, Bordetella / Q000037:antagonists & inhibitors; D014862:Wasp Venoms / Q000819:agonists
D000908:Antibodies, Fungal; D020346:Aquaporins; D002147:Calmodulin; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D010566:Virulence Factors, Bordetella; D014862:Wasp Venoms; D008627:Mercuric Chloride; C037500:mastoparan; D015544:Inositol 1,4,5-Trisphosphate; D037342:Pertussis Toxin; D020962:Heterotrimeric GTP-Binding Proteins; D020727:ADP-Ribosylation Factors; D009355:Neomycin; D002118:Calcium