Expression of a symbiosis-specific gene in Symbiodinium type A1 associated with coral, nudibranch and giant clam larvae

M Mies; C R Voolstra; C B Castro; D O Pires; E N Calderon; P Y G Sumida

doi:10.1098/rsos.170253

Expression of a symbiosis-specific gene in Symbiodinium type A1 associated with coral, nudibranch and giant clam larvae

R Soc Open Sci. 2017 May 24;4(5):170253. doi: 10.1098/rsos.170253. eCollection 2017 May.

Authors

M Mies¹, C R Voolstra², C B Castro^{3

4}, D O Pires^{3

4}, E N Calderon^{4

5}, P Y G Sumida¹

Affiliations

¹ Oceanographic Institute, University of São Paulo, Praça do Oceanográfico 191, 05508-120 São Paulo, SP, Brazil.
² Red Sea Research Center, Division of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology, 23955-6900 Thuwal, Saudi Arabia.
³ Museu Nacional, Universidade Federal do Rio de Janeiro, Quinta da Boa Vista, s/n, 20940-040 Rio de Janeiro, RJ, Brazil.
⁴ Instituto Coral Vivo, Rua dos Coqueiros, 87-45807-000 Santa Cruz Cabrália, BA, Brazil.
⁵ Núcleo em Ecologia e Desenvolvimento Socioambiental de Macaé, Universidade Federal do Rio de Janeiro, Av São José do Barreto, 764-27965-045 Macaé, RJ, Brazil.

Abstract

Symbiodinium are responsible for the majority of primary production in coral reefs and found in a mutualistic symbiosis with multiple animal phyla. However, little is known about the molecular signals involved in the establishment of this symbiosis and whether it initiates during host larval development. To address this question, we monitored the expression of a putative symbiosis-specific gene (H⁺-ATPase) in Symbiodinium A1 ex hospite and in association with larvae of a scleractinian coral (Mussismilia hispida), a nudibranch (Berghia stephanieae) and a giant clam (Tridacna crocea). We acquired broodstock for each host, induced spawning and cultured the larvae. Symbiodinium cells were offered and larval samples taken for each host during the first 72 h after symbiont addition. In addition, control samples including free-living Symbiodinium and broodstock tissue containing symbionts for each host were collected. RNA extraction and RT-PCR were performed and amplified products cloned and sequenced. Our results show that H⁺-ATPase was expressed in Symbiodinium associated with coral and giant clam larvae, but not with nudibranch larvae, which digested the symbionts. Broodstock tissue for coral and giant clam also expressed H⁺-ATPase, but not the nudibranch tissue sample. Our results of the expression of H⁺-ATPase as a marker gene suggest that symbiosis between Symbiodinium and M. hispida and T. crocea is established during host larval development. Conversely, in the case of B. stephanieae larvae, evidence does not support a mutualistic relationship. Our study supports the utilization of H⁺-ATPase expression as a marker for assessing Symbiodinium-invertebrate relationships with applications for the differentiation of symbiotic and non-symbiotic associations. At the same time, insights from a single marker gene approach are limited and future studies should direct the identification of additional symbiosis-specific genes, ideally from both symbiont and host.

Keywords: ATPase; Tridacna; larval ecology; scleractinia; sea slug; zooxanthellae.