A Functional Genomics View of Gibberellin Metabolism in the Cnidarian Symbiont Breviolum minutum

Abstract

Dinoflagellate inhabitants of the reef-building corals exchange nutrients and signals with host cells, which often benefit the growth of both partners. Phytohormones serve as central hubs for signal integration between symbiotic microbes and their hosts, allowing appropriate modulation of plant growth and defense in response to various stresses. However, the presence and function of phytohormones in photosynthetic dinoflagellates and their function in the holobionts remain elusive. We hypothesized that endosymbiotic dinoflagellates may produce and employ phytohormones for stress responses. Using the endosymbiont of reef corals Breviolum minutum as model, this study aims to exam whether the alga employ analogous signaling systems by an integrated multiomics approach. We show that key gibberellin (GA) biosynthetic genes are widely present in the genomes of the selected dinoflagellate algae. The non-13-hydroxylation pathway is the predominant route for GA biosynthesis and the multifunctional GA dioxygenase in B. minutum has distinct substrate preference from high plants. GA biosynthesis is modulated by the investigated bleaching-stimulating stresses at both transcriptional and metabolic levels and the exogenously applied GAs improve the thermal tolerance of the dinoflagellate. Our results demonstrate the innate ability of a selected Symbiodiniaceae to produce the important phytohormone and the active involvement of GAs in the coordination and the integration of the stress response.

Environmental Concentrations of Herbicide Prometryn Render Stress-Tolerant Corals Susceptible to Ocean Warming

“…Changes in the numbers of the OJIP transients further substantiate the synergistic impact of co-stress on photochemical electron transport, consequently exerting stronger effects on the photosynthesis of Symbiodiniaceae (Figures g and h). A recent study demonstrated that phytohormones play vital roles in signal transduction pathways in the response of the bleaching-inducible environmental stresses . The change in the relative abundance of salicylic acid (SA) may imply that the level of metabolic response to environmental stress of Symbiodiniaceae had increased under co-stress conditions (Figure c).…”

“…A recent study demonstrated that phytohormones play vital roles in signal transduction pathways in the response of the bleaching-inducible environmental stresses. 48 The change in the relative abundance of salicylic acid (SA) may imply that the level of metabolic response to environmental stress of Symbiodiniaceae had increased under co-stress conditions (Figure 3c). Accordingly, the co-stress elicited a notable increase in chlorophyll c content and chlorophyll metabolite levels on the fourth day, potentially serving as a compensatory mechanism within the coral that enhances photosynthetic efficiency (Figure S8).…”