AUTHOR=Yuyama Ikuko , Higuchi Tomihiko , Mezaki Takuma , Tashiro Hisako , Ikeo Kazuho 

TITLE=Metatranscriptomic Analysis of Corals Inoculated With Tolerant and Non-Tolerant Symbiont Exposed to High Temperature and Light Stress

JOURNAL=Frontiers in Physiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2022.806171

DOI=10.3389/fphys.2022.806171

ISSN=1664-042X

ABSTRACT=<p>Algal symbionts of corals can influence host stress resistance; for example, in the Pacific Ocean, whereas <italic>Cladocopium</italic> (C-type) is generally dominant in corals, <italic>Durusdinium</italic> (D-type) is found in more heat-resistant corals. Thus, the presence of D-type symbiont likely increases coral heat tolerance, and this symbiotic relationship potentially provides a hint to increase the stress tolerance of coral–algal symbioses. In this study, transcriptome profiles of <italic>Cladocopium-</italic> and <italic>Durusdinium</italic>-harboring <italic>Acropora solitaryensis</italic> (C-coral and D-coral, respectively) and algal photosystem functioning (<italic>F</italic><sub><italic>v</italic></sub><italic>/F</italic><sub><italic>m</italic></sub>) under bleaching conditions (high temperature and light stress) were compared. Stress treatment caused algal photoinhibition that the <italic>F</italic><sub><italic>v</italic></sub>/<italic>F</italic><sub><italic>m</italic></sub> value of Symbiodiniaceae was immediately reduced. The transcriptome analysis of corals revealed that genes involved in the following processes were detected: endoplasmic reticulum (ER) stress, mitophagy, apoptosis, endocytosis, metabolic processes (acetyl-CoA, chitin metabolic processes, etc.), and the PI3K-AKT pathway were upregulated, while DNA replication and the calcium signaling pathway were downregulated in both C- and D-corals. These results suggest that unrepaired DNA and protein damages were accumulated in corals under high temperature and light stress. Additionally, some differentially expressed genes (DEGs) were specific to C- or D-corals, which includes genes involved in transient receptor potential (TRP) channels and vitamin B metabolic processes. Algal transcriptome analysis showed the increased expression of gene encoding photosystem and molecular chaperone especially in D-type symbiont. The transcriptome data imply a possible difference in the stress reactions on C-type and D-type symbionts. The results reveal the basic process of coral heat/light stress response and symbiont-type-specific coral transcriptional responses, which provides a perspective on the mechanisms that cause differences in coral stress tolerance.</p>