Coral thermal tolerance: tuning gene expression to resist thermal stress.

Anthony J Bellantuono,David J Miller,Ove Hoegh-Guldberg,Mauricio Rodriguez-Lanetty,Camila Granados-Cifuentes,Sebastian C A Ferse

doi:10.1371/journal.pone.0050685

Abstract

The acclimatization capacity of corals is a critical consideration in the persistence of coral reefs under stresses imposed by global climate change. The stress history of corals plays a role in subsequent response to heat stress, but the transcriptomic changes associated with these plastic changes have not been previously explored. In order to identify host transcriptomic changes associated with acquired thermal tolerance in the scleractinian coral Acropora millepora, corals preconditioned to a sub-lethal temperature of 3°C below bleaching threshold temperature were compared to both non-preconditioned corals and untreated controls using a cDNA microarray platform. After eight days of hyperthermal challenge, conditions under which non-preconditioned corals bleached and preconditioned corals (thermal-tolerant) maintained Symbiodinium density, a clear differentiation in the transcriptional profiles was revealed among the condition examined. Among these changes, nine differentially expressed genes separated preconditioned corals from non-preconditioned corals, with 42 genes differentially expressed between control and preconditioned treatments, and 70 genes between non-preconditioned corals and controls. Differentially expressed genes included components of an apoptotic signaling cascade, which suggest the inhibition of apoptosis in preconditioned corals. Additionally, lectins and genes involved in response to oxidative stress were also detected. One dominant pattern was the apparent tuning of gene expression observed between preconditioned and non-preconditioned treatments; that is, differences in expression magnitude were more apparent than differences in the identity of genes differentially expressed. Our work revealed a transcriptomic signature underlying the tolerance associated with coral thermal history, and suggests that understanding the molecular mechanisms behind physiological acclimatization would be critical for the modeling of reefs in impending climate change scenarios.

Highlights

Coral reefs are of incredible value to human society, with a half billion people dependent on reefs which have been estimated to provide ecosystem services worth $375 billion per year [1,2,3]
We present the first evidence of the transcriptional response of the host associated with acquired thermal tolerance in A. millepora, along with the profile of thermal injury observed in non-preconditioned corals
Sustained-1 treatment (S1) tanks were subjected to ten days of 28uC thermal preconditioning prior to a 31uC thermal challenge, while sustained-2 (S2) treatment was heated to 28uC for 17 days prior to exposure to 31uC thermal challenge

Summary

Introduction

Coral reefs are of incredible value to human society, with a half billion people dependent on reefs which have been estimated to provide ecosystem services worth $375 billion per year [1,2,3]. This vast resource may be rapidly diminished by coral bleaching, a loss of the mutualistic intracellular dinoflagellates, Symbiodinium, and/or loss of photosynthetic pigments [4], originally described by Glynn in 1984 [5]. Corals need to markedly increase their thermal tolerance at a rate of 0.2 to 1.0 ̊C per decade by adaptive or acclimative processes [10]. The exploration of physiological limits of corals and underlying molecular signatures is of great importance in predicting the fate of corals in decades to come

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