The photon menace: kleptoplast protection in the photosynthetic sea slug Elysia timida

Absorption of excessive light by photosymbiotic organisms leads to the production of reactive oxygen species that can damage both symbiont and host. This is highly relevant in sacoglossan sea slugs that host functional chloroplasts ‘stolen’ from their algal foods (kleptoplasts), because of limited repair capacities resulting from the absence of algal nuclear genes. Here, we experimentally demonstrate (i) a host-mediated photoprotection mechanism in the photosynthetic sea slug Elysia timida, characterized by the closure of the parapodia under high irradiance and the reduction of kleptoplast light exposure; and (ii) the activation of a reversible xanthophyll cycle in kleptoplasts, which allows excessive energy to be dissipated. The described mechanisms reduce photoinactivation under high irradiance. We conclude that both host-mediated behavioural and plastid-based physiological photoprotective mechanisms can mitigate oxidative stress induced by high light in E. timida. These mechanisms may play an important role in the establishment of long-term photosynthetically active kleptoplasts.

This work was supported by Programa Investigador, contract IF/00899/2014; by R&D project HULK - PTDC/BIA-ANM/4622/2014 – POCI-01-0145-FEDER-016754 funded by Fundo Europeu de Desenvolvimento Regional (FEDER), through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI), and by national funds (OE); and by support to CESAM through UID/AMB/50017/2019 (Fundação para a Ciência e a Tecnologia/Ministério da Ciência, Tecnologia e Ensino Superior, FCT/MCTES). P.C. was funded by FCT in the scope of the framework contract foreseen in numbers 4, 5 and 6 of article 23 of the Decree-Law 57/2016, of 29 August, changed by Law 57/2017, of 19 July.

Peer reviewed