title: Gene expression patterns of the coralAcropora milleporain response to contact with macroalgae.
abstract: Contact with macroalgae often causes coral mortality, but the roles of abrasion versus shading versus allelopathy in these interactions are rarely clear and effects on gene expression are unknown. Identification of gene expression changes within corals in response to contact with macroalgae can provide insight into the mode of action of allelochemicals, as well as reveal transcriptional strategies of the coral that mitigate damage from this competitive interaction, enabling the coral to survive. Gene expression responses of the coralAcropora milleporaafter long-term (20 d) direct contact with macroalgae (Chlorodesmis fastigiata, Dictyota bartayresiana,Galaxaura filamentosaandTurbinaria conoides) and short-term (1 h and 24 h) exposure toC. fastigiatathalli and their hydrophobic extract were assessed. After 20 d of exposure,T. conoidesthalli elicited no significant change in visual bleaching or zooxanthellae PSII quantum yield withinA. milleporanubbins, but stimulated the greatest alteration in gene expression of all treatments.Chlorodesmis fastigiata, D. bartayresianaandG. filamentosacaused significant visual bleaching of coral nubbins and reduced the PSII quantum yield of associated zooxanthellae after 20 d, but elicited fewer changes in gene expression relative toT. conoidesat day 20. To evaluate initial molecular processes leading to reduction of zooxanthella PSII quantum yield, visual bleaching, and coral death, short-term exposures toC. fastigiatathalli and hydrophobic extracts were conducted; these interactions revealed protein degradation and significant changes in catalytic and metabolic activity within 24 h of contact. These molecular responses are consistent with the hypothesis that allelopathic interactions lead to alteration of signal transduction and an imbalance between reactive oxidant species production and antioxidant capabilities within the coral holobiont. This oxidative imbalance results in rapid protein degradation and eventually to apoptosis and/or necrosis when compensatory transcriptional action by the coral holobiont insufficiently mitigates damage by the allelochemicals ofC. fastigiata.
authors.affiliation: Georgia Institute of Technology, School of Biology, 310 Ferst Drive, Atlanta, GA 30332.
authors.forename: Tl
authors.initials: T
authors.lastname: Shearer
authors.forename: Db
authors.initials: D
authors.lastname: Rasher
authors.forename: Tw
authors.initials: T
authors.lastname: Snell
authors.forename: Me
authors.initials: M
authors.lastname: Hay
keywords: Allelopathy; Fiji; algal-coral competition; gene expression