Herbicide prometryn aggravates the detrimental effects of heat stress on the potential for mutualism of Symbiodiniaceae.

Ocean warming threatens the health of corals globally, and superimposed coastal environmental pollution can result in severe and irreversible coral bleaching. However, the responses of the coral symbiont Symbiodiniaceae to multiple stresses remain largely unknown. This study investigated the response of the coral symbiotic algae Cladocopium sp. to short-term exposure (4 days) to an environmentally relevant concentration (1 μg L) of the photosystem II (PSII) herbicide prometryn under heat stress (32 ℃) through physiological and omic analyses. These results showed that co-stress affected the photosynthetic efficiency of Cladocopium sp. negatively. Overproduction of reactive oxygen species and subsequent oxidative stress under co-stress activated distinct regulatory pathways in Cladocopium sp. Transcriptomic and proteomic analyses revealed that prometryn exacerbated heat stress-induced photosystem damage and reduced the regulatory capacity of Cladocopium sp. Moreover, co-stress disrupted energy metabolism, and further impaired nitrogen assimilation and nutrient transfer processes, potentially compromising the symbiotic potential between corals and Symbiodiniaceae. In summary, this study offers a valuable insight into understanding the molecular responses of Symbiodiniaceae to thermal and prometryn co-stress. It helps uncover the potential toxicity mechanisms induced by herbicide on coral symbionts in the context of climate change.