Short Term Exposure to Heat and Sediment Triggers Changes in Coral Gene Expression and Photo-Physiological Performance

Abstract

Corals, together with their endosymbiotic Symbiodiniaceae, are known to exhibit a suite of mechanisms for survival under stressful conditions. However, exactly how the host animal responds to varying environmental conditions remains unclear. In this study, we tested two relevant environmental factors that can have deleterious effects on corals: heat and sediment. We examined among-genotype responses of Pocillopora acuta to these factors with RNA-Seq in concert with widely-used tools for assessing the physiological conditions of corals. Heat and sediment treatments were applied in a 2 × 2 crossed experimental design: (1) ∼30 • C without sediment (control, "C"), (2) ∼30 • C with sediment (sediment-only, "S"), (3) ∼32 • C without sediment (heat-only, "H"), (4) ∼32 • C with sediment (heat + sediment, "H+S") over four consecutive days (3-h daily exposure) in ex situ aquarium conditions. A clear differentiation in gene expression patterns was observed in corals exposed to heat alone and to heat with sediment, relative to the control treatment. Few transcripts (∼3) were found to be differentially expressed for corals exposed to sediment only. The greater impact of heat was supported by photophysiological measurements that showed significant effects on maximum quantum yield and average symbiont density among genotypes of P. acuta. The combined effect of heat and sediment caused a greater reduction in average symbiont density than the effect of sediment alone. Furthermore, "H+S" disrupted the ability of corals to maintain processes involving assembly and disassembly of cilium which suggests a synergistic effect between the two factors. We also found that host-specific genes which were expressed differentially may not be related to their interactions with algal symbionts. Rather, these genes are involved in a variety of biological functions including, but not limited to, cilium biogenesis and degradation, cilia motility, innate and adaptive immune responses, cell adhesion and bone mineralization, and processes involved in the cell

Gene Expression and Photophysiological Changes in Pocillopora acuta Coral Holobiont Following Heat Stress and Recovery

“…During a more recent coral bleaching events in Singapore, the coral genus Pocillopora appeared to show a shift to being less susceptible [12,35], similar to observationsfrom the Great Barrier Reef, Australia [36,37]. While this genus is known to be highly plastic [24,38,39], the mechanisms underlying its enhanced resistance to and ability to recover from thermal stress remain unclear. Therefore, it is of interest to explore both photophysiological and transcriptional plasticity in Pocillopora, using Pocillopora acuta as the model species.…”

“…The selected genes of interest (GOIs) and internal control genes (ICGs) were derived from an RNA-Seq experiment conducted on P. acuta following heat exposure [38] as being the most responsive and stable, respectively. The transcript sequences used for primer designs were validated to be associated with corals only as reported in Poquita-Du et al [38]. The full list of candidate genes is shown in Table 1.…”

“…List of genes of interest (GOIs) and internal control genes (ICGs) (*) with their corresponding functional profile (biological process) and primer designs. Transcript sequences from Poquita-Du et al [38] that matched selected GOIs were consolidated for alignment by gene for primer design. Primers for each gene were designed using the online tool by NCBI that incorporated Primer3 and BLAST (https://www.ncbi.nlm.nih.gov/tools/primer-blast/, June 2017), specifying "Pocillopora acuta" in the target organism field.…”

Local acclimatisation‐driven differential gene and protein expression patterns of Hsp70 in Acropora muricata: Implications for coral tolerance to bleaching

“…The highest relative levels of host hsp70 were recorded in near‐coast and reef samples collected in summer 2016. Results are in line with laboratory and field studies that reported increases in hsp expression following high heat‐light stress (reviewed in Louis et al., 2017; Poquita‐Du et al., 2019; Traylor‐Knowles et al., 2017; Zhang et al., 2018).…”

New genus and species record of reef coral Micromussa amakusensis in the southern South China Sea

“…Also a well-studied 'lab rat' for experimental work in the Indo-Pacific (e.g. Ben-Haim et al 2003;Cumbo et al 2013;Poquita-Du et al 2019a), many P. damicornis-like colonies have been confirmed to be P. acuta at multiple localities, including Japan (Kitano et al 2015), Philippines (Torres and Ravago-Gotanco 2018), Singapore (Poquita-Du et al 2017), American Sāmoa (Montgomery et al 2019), Austral and Cook Islands (Mayfield et al 2015), and Hawai'i (Johnston et al 2018). These discoveries have wide-ranging impacts, even for the evaluation of species conservation status (see Agapow et al 2004;Mace 2004;Ely et al 2017).…”