Lipoxygenase-allene oxide synthase pathway in octocoral thermal stress response

Marine ecosystems are sensitive to elevated seawater temperature, with stony corals serving as model organisms for temperature-imposed declines in population viability and diversity. Several stress markers, including heat shock proteins, have been used for the detection and prediction of stress responses in stony corals. However, the stress indicators in soft corals remain elusive. In higher animals and plants, oxylipins synthesized by fatty acid di- and monooxygenases contribute to stress-induced signaling; however, the role of eicosanoid pathways in corals remains unclear. The eicosanoid gene specific to corals encodes for a natural fusion protein of allene oxide synthase and lipoxygenase (AOS-LOX). In this work, using the easily cultivated soft coral Capnella imbricata as the stress response model, we monitored the expression of the AOS-LOX and the formation of arachidonic acid metabolites in response to an acute rise in water temperature. Gene expression profiles of two 70 kDa heat shock proteins (Hsps: Hsp70 and Grp78) were used as a positive control for the stress response. In comparison with normal seawater temperature (23 A degrees C), AOS-LOXa and Hsps were all up-regulated after modest (28 A degrees C) and severe (31 A degrees C) temperature elevation. While the up-regulation of AOS-LOXa and Grp78 was more sensitive to moderate temperature changes, Hsp70s were more responsive to severe heat shock. Concurrently, endogenous and exogenous AOS-LOXa-derived eicosanoids were up-regulated. Thus, together with the up-regulation of AOS-LOX by other abiotic and biotic stress stimuli, these data implicate AOS-LOX as part of the general stress response pathway in corals.