Aposymbiotic Plesiastrea versipora continues to produce cell-signalling molecules that regulate the carbon metabolism of symbiotic algae

Abstract

The scleractinian coral Plesiastrea versipora produces cell signals that regulate the carbon metabolism of its symbiotic algae. Host release factor (HRF) stimulates the release of photosynthate, and photosynthesis inhibiting factor (PIF) partially inhibits carbon fixation in freshly isolated symbiotic algae. Naturally occurring aposymbiotic specimens of P. versipora are rare in Port Jackson, Australia, but one that was collected contained HRF and PIF. Artificially produced aposymbiotic corals of P. versipora that had been kept in the dark for up to 23 months continued to produce both HRF and PIF in the absence of photosynthetically active algae. Aposymbiotic P. versipora from which most of the tissue had been removed, regenerated when they were kept in the dark and fed; the regenerated tissue also contained HRF and PIF. These results suggest that the presence of symbiotic algae is not required for the production of HRF and PIF in P. versipora. We suggest that these cell signals may have evolved in response to symbiosis with Symbiodinium sp. but are now always expressed in the coral P. versipora.