Chemotaxis of fungal zoospores, with special reference to Aphanomyces cochlioides

Zoospores of phytopathogenic fungi accumulate at the potential infection si tes of host roots by chemotaxis. The aggregated spores then adhere, encyst, germinate, and finally penetrate into the root tissues to initiate infecti on. Some of the host-specific attractants have already been identified. The host-specific attractants also induce cell differentiation of certain zoos pores under laboratory conditions. This indicates that a signal released fr om the roots of the host plant guides the pest propagules for orientation a nd prepares them for establishing a host-pathogen relationship by necessary physiological changes. Some non-host plant secondary metabolites were foun d to markedly regulate behavior and viability of zoospores, suggesting that non-host compounds may also play a role in protecting the nonhost plants f rom the attack of zoosporic fungi. We hypothesized that zoospores perceive the host signal(s) by specific G-protein-coupled receptors and translate it into responses by way of the phosphoinositide-Ca2+ Signaling cascade. The details of the signal transduction mechanism in fungal zoospores are yet to be discovered. In this report, we review the signaling and communications between phytopathogenic fungal zoospores and host and non-host plants with special reference to Aphanomyces cochlioides.