Genomic adaptations to an endolithic lifestyle in the coral-associated alga Ostreobium

• DOI: 10.1016/j.cub.2021.01.018
• Publication Date: 2021-02-06T12:57:46Z
• Authors: Cintia Iha; Katherine E. Dougan; Javier A. Varela; Viridiana Avila; Christopher J. Ja...; Kenny A. Bogaert; Yibi Chen; Louise M. Judd; Ryan Wick; Kathryn E. Holt; Marisa M. Pasella; Francesco Ricci; Sonja I. Repetti; Mónica Medina; Vanessa R. Marcelino; Cheong Xin Chan; Heroen Verbruggen
• Keywords: Holobiont; Coral bleaching

SummaryThe green algaOstreobiumis an important coral holobiont member, playing key roles in skeletal decalcification and providing photosynthate to bleached corals that have lost their dinoflagellate endosymbionts.Ostreobiumlives in the coral’s skeleton, a low-light environment with variable pH and O□ availability. We present theOstreobiumnuclear genome and a metatranscriptomic analysis of healthy and bleached corals to improve our understanding ofOstreobium’s adaptations to its extreme environment and its roles as a coral holobiont member. TheOstreobiumgenome has 10,663 predicted protein-coding genes and shows adaptations for life in low and variable light conditions and other stressors in the endolithic environment. This alga presents a rich repertoire of light-harvesting complex proteins but lacks many genes for photoprotection and photoreceptors. It also has a large arsenal of genes for oxidative stress response. An expansion of extracellular peptidases suggests thatOstreobiummay supplement its energy needs by feeding on the organic skeletal matrix, and a diverse set of fermentation pathways allow it to live in the anoxic skeleton at night.Ostreobiumdepends on other holobiont members for vitamin B12, and our metatranscriptomes identify potential bacterial sources. Metatranscriptomes showedOstreobiumbecoming a dominant agent of photosynthesis in bleached corals and provided evidence for variable responses among coral samples and differentOstreobiumgenotypes. Our work provides a comprehensive understanding of the adaptations ofOstreobiumto its extreme environment and an important genomic resource to improve our comprehension of coral holobiont resilience, bleaching and recovery.