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

Ikuko Yuyama; Tomihiko Higuchi; Takuma Mezaki; Hisako Tashiro; Kazuho Ikeo

doi:10.3389/fphys.2022.806171

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

Front Physiol. 2022 Apr 11:13:806171. doi: 10.3389/fphys.2022.806171. eCollection 2022.

Authors

Ikuko Yuyama¹, Tomihiko Higuchi², Takuma Mezaki³, Hisako Tashiro⁴, Kazuho Ikeo⁴

Affiliations

¹ Graduate School of Science and Technology for Innovation, Yamaguchi University, Yamaguchi, Japan.
² Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan.
³ Kuroshio Biological Research Foundation, Otsuki, Japan.
⁴ Department of Genomics and Evolutionary Biology, National Institute of Genetics, Mishima, Japan.

Abstract

Algal symbionts of corals can influence host stress resistance; for example, in the Pacific Ocean, whereas Cladocopium (C-type) is generally dominant in corals, Durusdinium (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 Cladocopium- and Durusdinium-harboring Acropora solitaryensis (C-coral and D-coral, respectively) and algal photosystem functioning (F _v /F _m ) under bleaching conditions (high temperature and light stress) were compared. Stress treatment caused algal photoinhibition that the F _v /F _m 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.

Keywords: Acropora solitaryensis; Cladocopium; Durusdinium; RNA-seq; coral bleaching; endosymbiosis.