11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 5: Functional Biology of Corals and Coral Symbiosis: Molecular Biology, Cell Biology and Physiology
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Differential Expression Of Genes Between Light And Dark Calcification
Aurélie MOYA* 1,2 , Sylvie TAMBUTTÉ 1 , Guillaume BÉRANGER 3,4 , Béatrice
GAUME 1 , Jean-Claude SCIMECA 3 , Séverine LOTTO 1 , Denis ALLEMAND 1 , Didier
ZOCCOLA 1
1 Centre Scientifique de Monaco, Monaco, Monaco, 2 , University of Nice-Sophia
Antipolis, UMR 1112 INRA-UNSA, NICE Cedex 2, France, 3 Faculté de Médecine,
GéPITOS, K 2943, CNRS, NICE Cedex 02, France, 4 - Research Institute of Molecular
Pathology, Vienna, Austria
Most scleractinian corals establish a symbiotic relationship with phototrophic
dinoflagellates. This symbiosis is responsible for the “light-enhanced calcification”
(LEC) phenomenon in corals. Despite numerous researches on this phenomenon, the
mechanisms by which photosynthetic symbionts enhance calcification still remain
enigmatic. In order to characterize the LEC in corals we tested the hypothesis that coral
genes are differentially expressed between light and dark calcification. As a preliminary
approach, the differential expression of three genes involved in calcium and bicarbonate
supply for calcification (Ca channel, Ca ATPase, and carbonic anhydrase) was tested
between light and dark conditions in the coral Stylophora pistillata, using the real-time
Polymerase Chain Reaction as a technique.
For this purpose, we first cloned and sequenced a housekeeping gene, 36B4 gene from
the coral Stylophora pistillata. We then validated 36B4 and ß-actin as housekeeping
genes and two photosynthetic genes (Rubisco and D1 protein of the photosystem II) as
positive control genes between light and dark conditions.
Finally, we determined that the two genes encoding proteins involved in calcium
transport for coral calcification (a calcium ATPase and a calcium channel) do not show
differential expression between light and dark conditions, while the gene encoding a
carbonic anhydrase is two-fold more expressed in the dark than in the light. We suggest
that up-regulation of the gene encoding a carbonic anhydrase in the dark allows to cope
with night acidosis of tissues.
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Photoacclimation, Photoadaptation And Coral Bleaching
Roberto IGLESIAS-PRIETO* 1
1 Instituto de Ciencias del Mar y Limnología, Unidad Académica Puerto Morelos,
Universidad Nacional Autónoma de México, Cancún, Mexico
During the last 200 million years scleractinian corals in symbioses with photosynthetic
dinoflagellates have been responsible for the formation and maintenance of coral reefs. In
these organisms, algal photosynthesis can provide more that a 100% of the basal
metabolic requirements. The nutritional advantages that symbiotic invertebrates obtain
from the translocation and consumption of algal photosynthates can explain why
symbiotic corals possess significantly larger calcification rates relative to non-symbiotic
invertebrates. In this context, algal photosynthesis is a key element in the formation of
modern coral reefs. Considering the importance of algal photosynthesis for the well being
of symbiotic corals, the study of the photobiology of these organisms has attracted
significant attention. Symbiotic corals inhabit the entire photic zone and are subject to
extraordinary variations in light intensity. I will review the physiological mechanisms
employed by corals and their symbiotic algae to successfully harvest and utilize the
available solar radiation. Based on comparative analyses of the differential responses of
individual algal species to variations in growth irradiance in culture, or intact associations
in nature, it has been postulated that the differential utilization of solar radiation is an
important axis for niche diversification among reef-building corals. Recent analyses of
the optical properties of intact coral surfaces using transmittance determinations indicate
that due to the multiple scattering on the highly reflective aragonite skeleton, the specific
absorption coefficients of the symbiotic algae are much higher that those obtained from
freshly isolated algae, making symbiotic scleractinians one of the most efficient solar
collector in nature. The role of the animal skeleton in modulating the absorption
properties of the symbiotic algae has profound implications for our understanding of the
evolution of these organisms. Finally, I will discuss the role of multiple scattering of
coral skeletons in the propagation of thermal stress, leading to coral bleaching.
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Thermal Stress Stimulates The Production Of Nitric Oxide in symbiodinium
Microadriaticum : Is Nitric Oxide A Key Molecule in The Coral Bleaching
Phenomenon?
Josée Nina BOUCHARD* 1 , Hideo YAMASAKI 1
1 University of the Ryukyus, Nishihara, Japan
In a recent study, nitric oxide (NO) has been suggested to be implicated in the mechanism
leading to the expulsion of symbiotic algae from the coral host during a thermal stress event. In
this previous study, the production of NO was attributed exclusively to the coral host and not to
its algal symbionts. Recently, the production of NO has been shown to occur in diverse species
of marine microalgae and to act as a signal molecule of stress response and/or as an indicator of
growth status. These findings prompted us to determine whether coral symbiotic microalgae
also produce NO both under normal growth and thermal stress conditions. Our results showed
that Symbiodinium microadriaticum grown under laboratory conditions can produce NO when
supplemented with either sodium nitrite or L-arginine as a substrate. The production of NO was
confirmed by electrochemical and fluorimetric techniques. Microscopic observations of cells
marked with the NO fluorescent dye DAF-2 DA also confirmed that NO was truly produced
inside the microalgal cells. Ultimately, when S. microadriaticum were exposed to an acute heat
stress (from 27 to 41 °C) the production of NO increased along with the increasing temperature.
This increase in temperature was also associated with a decline in the physiological state of the
cells as observed by a decline in the Fv/Fm values. Results from the present study are the first to
unambiguously report that zooxanthellae can synthesize NO even when they are not in a
symbiotic association with a coral host. The increase in NO production upon heat stress
suggests that NO can be synthesized upon exposure of the microalgae to stressful
environmental conditions. The possible implications of such findings are discussed in the light
of the coral bleaching phenomenon which is associated with global warming.
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Induced Bleaching Of Stylophora Pistillata By Darkness Stress And Its Subsequent
Recovery
Zvy DUBINSKY* 1 , Shachar KOREN 1 , Osnat CHOMSKY 2
1 Life Sciences, Bar Ilan University, Ramat Gan, Israel, 2 Biology, National Institute of
Oceanography IOLR, Haifa, Israel
Bleaching, the visible effect of losing zooxanthellae by corals, has been observed with
increasing frequency in most of the world’s reefs. Since it usually leads to coral colony death
and whole reef destruction, it has been the subject of several studies in recent years. In the
present article we describe a method to causing complete, but reversible, bleaching in the
common Red Sea coral, Stylophora pistillata by darkness stress. That treatment affects the coral
by reducing the density of the zooxanthellae, the endosymbiotic algae living within the coral’s
cells, causing the animal tissue to lose pigmentation. After 8 days in the dark the coral begins to
show visible bleaching, which a week later progressed to 70%, and by the 44th day we obtained
complete bleaching. At that time no zooxanthellae or chlorophyll were detected in the coral
tissue. Following the transferal of the corals to darkness, at first the algal cells exhibit a
photoacclimative response, accumulating chlorophyll up to 10 fold of the initial values.
Fragments that were 70% bleached showed full recovery 30 days after having been returned to
light. In the course of recovery, cellular chlorophyll gradually decreased to control – and initial
concentrations
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