Engineering Strategies to Decode and Enhance the Genomes of Coral Symbionts

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.

Photo-movement in the sea anemone Aiptasia influenced by light quality and symbiotic association

“…The effect of the symbiont on the phototropic and phototactic responses differed depending on the host; thus it cannot be assumed that the same phenotype will be elicited when different symbionts are paired with various host animals. As enhancing the genome of coral symbionts and assisted evolution have been suggested as potential ways to increase reef resilience in the face of climate change (van Oppen et al 2015;Levin et al 2017), it will be critical to better understand hostsymbiont interactions. Aiptasia provides a strong model system to explore these interactions.…”

The past, present, and future of coral heat stress studies

“…Symbiodiniaceae research continues to uncover complex interactions and response mechanisms, often relating to oxidative stress (ROS and NO stress (Abrego et al, 2008;Bouchard & Yamasaki, 2008; DeSalvo, Sunagawa, Fisher, et al, 2010; Hume F I G U R E 2 Summary of coral heat stress responses. Symbiodiniaceae have their own temperature tolerance and responses but also produce ROS under stress, which can leak into the host and exacerbate oxidative stress Hume et al, 2016;Levin et al, 2017;Littman, Bourne, & Willis, 2010;Middlebrook, Hoegh-Guldberg, & Leggat, 2008)), nutrient exchange, and metabolic compatibility (Davy, Allemand, & Weis, 2012;Rädecker et al, 2018;Suggett, Warner, & Leggat, 2017;Wiedenmann et al, 2012). Meanwhile, the metabolic rate is also increased, causing an increase not only in reactive oxygen species (ROS) but also in nitric oxide (NO).…”

“…Consequently, oxidative stress from ROS and NO is experienced by the coral, which can ultimately lead to apoptosis or necrosis. Symbiodiniaceae have their own temperature tolerance and responses but also produce ROS under stress, which can leak into the host and exacerbate oxidative stress Hume et al, 2016;Levin et al, 2017;Littman, Bourne, & Willis, 2010;Middlebrook, Hoegh-Guldberg, & Leggat, 2008)), nutrient exchange, and metabolic compatibility (Davy, Allemand, & Weis, 2012;Rädecker et al, 2018;Suggett, Warner, & Leggat, 2017;Wiedenmann et al, 2012).…”

Harnessing synthetic biology for kelp forest conservation1

“…), and boost resilience of coral reefs to changing climate conditions (Levin et al. , Cleves et al. ).…”