Host-specific plant signal and G-protein activator, mastoparan, trigger differentiation of zoospores of the phytopathogenic oomycete Aphanomyces cochlioides

摘要

We found that the gradient of a host-specific attractant, cochliophilin A (5-hydroxy-6,7-rnethylenedioxyflavone) isolated from the roots of spinach triggered encystment followed by germination of zoospores of Aphanomyces cochlioides at a concentrationless than micromolar order. This compound did not affect the growth and reproduction of this phytopathogen up to 10~(-6 )M concentration in the culture medium. We also observed that mastoparan, an activator of heterotrimeric G-protein could inhibit themotility of zoospores and then strikingly effect encystment followed by 60-80% germination of cysts. Concomitant application of cochliophilin A and mastoparan showed stronger encystment followed by 100% germination of cysts. In addition, we have observedthat chemicals interfering with phospholipase C activity (neomycin) and Ca~(2+) influx/release (EGTA and loperamide) suppress cochliophilin A or mastoparan induced encystment and germination. These results suggest that G-protein mediated signal transduction mechanism may be involved in the differentiation of the A. cochlioides zoospores. This is the first report on the differentiation of oomycete zoospores initiated by a host-specific plant signal or a G-protein activator.