Cell Signaling in the Chemoaccumulation Response of the Colonial Green Alga Astrephomene Gubernaculifera

Abstract

Abstract A. gubernaculifera can grow on acetate even in the dark. Interestingly, it displays a well‐developed chemoaccumulation response to added acetate. We suggest that this chemoaccumulation results from a receptor‐based signaling pathway because the alga responds to the structurally similar molecule propionate even though the latter compound cannot support growth. Based on suggestions about chemotactic signaling pathways in other eukaryotes and postulated phototactic response of some algae, we hypothesized that the signaling pathway involves heterotrimeric G‐proteins. The effectiveness of the chemoresponse was determined by measuring the diameter of the chemoaccumulation cloud after addition of 10 mL aliquots of media containing acetate to colonies swimming in media without acetate. Neomycin, which inhibits the G‐protein dependent activity of phospholipase C, completely inhibited chemoaccumulation at 100 mM, and markedly reduced the density of the accumulation response at 10 mM with no obvious changes in general colonial motility. EGTA, a calcium chelator, abolished the chemoresponse. Mastoporan, a G‐protein activator, caused accumulation even in the absence of acetate. These results support the hypothesis that chemoaccumulation in A. gubernaculifera uses a G‐protein mediated, calcium‐dependent, cell‐signaling pathway.