Engineering Strategies to Decode and Enhance the Genomes of Coral Symbionts.

Rachel A Levin,David J Suggett,Shobhit Agrawal,Peter D Steinberg,Madeleine J H Van Oppen,Christian R Voolstra

doi:10.3389/fmicb.2017.01220

Abstract

Elevated sea surface temperatures from a severe and prolonged El Niño event (2014–2016) fueled by climate change have resulted in mass coral bleaching (loss of dinoflagellate photosymbionts, Symbiodinium spp., from coral tissues) and subsequent coral mortality, devastating reefs worldwide. Genetic variation within and between Symbiodinium species strongly influences the bleaching tolerance of corals, thus recent papers have called for genetic engineering of Symbiodinium to elucidate the genetic basis of bleaching-relevant Symbiodinium traits. However, while Symbiodinium has been intensively studied for over 50 years, genetic transformation of Symbiodinium has seen little success likely due to the large evolutionary divergence between Symbiodinium and other model eukaryotes rendering standard transformation systems incompatible. Here, we integrate the growing wealth of Symbiodinium next-generation sequencing data to design tailored genetic engineering strategies. Specifically, we develop a testable expression construct model that incorporates endogenous Symbiodinium promoters, terminators, and genes of interest, as well as an internal ribosomal entry site from a Symbiodinium virus. Furthermore, we assess the potential for CRISPR/Cas9 genome editing through new analyses of the three currently available Symbiodinium genomes. Finally, we discuss how genetic engineering could be applied to enhance the stress tolerance of Symbiodinium, and in turn, coral reefs.

Highlights

Photosynthetic dinoflagellates are critical primary producers in the aquatic environment, yet, their functional genomics are largely unexplored (Leggat et al, 2011; Murray et al, 2016)
Genetic engineering has been central to the study of gene function and phenotypic enhancement in organisms ranging from microbes to mammals and a key platform for socioeconomic industries and biotechnologies; yet only two cases of transgene expression in Symbiodinium have ever been validated
By evaluating the rapidly increasing supply of next-generation sequencing (NGS) data, we propose a genetic engineering framework for Symbiodinium that may markedly advance our understanding of these important dinoflagellates

Summary

Introduction

Photosynthetic dinoflagellates are critical primary producers in the aquatic environment, yet, their functional genomics are largely unexplored (Leggat et al, 2011; Murray et al, 2016). Genetic factors that promote differences in stress tolerance between Symbiodinium variants (both inter- and intra-specific) strongly influence coral gene expression and bleaching susceptibility (Berkelmans and van Oppen, 2006; DeSalvo et al, 2010; Yuyama et al, 2012; Levin et al, 2016).

Results

Conclusion