Recently, the group of Haibin Zhang published a research article titled "Genetic adaptations of sea anemone to hydrothermal environment" in Science Advances (TOP). This study has deciphered the chromosome-level genome of the deep-sea anemone Alvinactis idsseensis sp. nov., which inhabits the hydrothermal vents of the Central Indian Ridge (Edmond). The results elucidate the survival mechanisms of anemones in the extreme environment of deep-sea hydrothermal vents.

Deep-sea hydrothermal vents are characterized by extreme temperatures and pressures, high concentrations of metal ions, toxic chemicals, and perpetual darkness, but a large number of organisms thrive here, establishing a unique and fascinating ecosystem. Edmond and Kairei are two hydrothermal vents on the Central Indian Ridge, exhibit a high degree of geographic connectivity. The content of various metal ions (such as Fe ²⁺, Mn ²⁺, Cu ²⁺, Zn ²⁺, Cd ²⁺, and Pb ²⁺) in them is much higher than that of the surrounding seawater. This anemone is the dominant species living in the Edmond hydrothermal vent. It is commonly found in the surrounding areas of sulfide-rich hydrothermal vents (with a habitat temperature of 1 ~ 2℃). It mainly obtains nutrition by preying on blind shrimps  but there are few studies on the adaptation mechanism of this anemone to extreme environments . 

Figure 1 Sampling information

Through comparative genomic analysis, the research team found that 736/31 gene families in the anemone genome were significantly expanded/contracted. The expanded gene families are primarily associated with metal ion binding, cell membranes, and stress responses. Notably, the MTP gene family, related to metal ion tolerance, has expanded significantly. Transcriptome analysis revealed that the majority of MTP genes are predominantly expressed in the tentacles. Given the limited research on MTPs in invertebrates, to better understand the functions of MTPs, researchers utilized a yeast expression system for functional validation. The results demonstrated that yeast cells harboring MTPs could only grow in media containing high concentrations of Fe²⁺ and Mn²⁺. This evidence confirms that MTPs can help the anemone tolerate high concentrations of Fe ²⁺ and Mn ²⁺ in the Edmond hydrothermal vent environment.

Although Fe²⁺ is an essential component of biological functional such as oxygen transport in all organisms, excessive iron can lead to the production of peroxides. Therefore, maintaining cellular iron homeostasis is crucial for the normal molecular functions of living organisms. This study found that the fech gene detected positive selection signal sites (P283H) and mutation sites (N279H) in the highly conserved ferrochelatase domain, indicating that the fech gene may increase the ability of the anemone to bind iron or other metal ions. In addition, it was found that genes related to the formation of Fe-S clusters ( nfs and fxn ) were positively selected, and the collaboration between these genes may play an important role in maintaining cellular metal ion homeostasis in this anemone.

Figure 2 Adaptability of deep-sea anemones to metal ions

High hydrostatic pressure can affect cell membrane fluidity, protein stability, DNA structure, and cytoskeleton. This study combined the published deep-sea anemones (Paraphelliactis xishaensis ) genome, and found that 22 gene families had co-expanded in the two deep-sea anemones. Enrichment analysis found that these gene families were related to DNA repair and cell membranes . To further analyze the impact of high hydrostatic pressure on cell membrane function, the researchers compared the total lipid content of this anemone and shallow-water sea anemones and found that these two anemones had a higher content of polyunsaturated fatty acids than shallow-sea anemones. Interestingly, multiple genes involved in the synthesis of unsaturated fatty acids (fasn, acss3, pfi, and Rv3720) have changed, among which fasn in the Mariana snailfish Pseudoliparis swirei genome, which may be a convergent evolution of deep-sea organisms to cope with high hydrostatic pressure.

Figure 3 Adaptation to high hydrostatic pressure in deep-sea anemones

This study also discovered that this anemone may enhance its infrared sensing capabilities through more sensitive opsins to aid in the predation of blind shrimp in dark environments. Additionally, it possesses a complete set of circadian rhythm pathway genes, which may contribute to its survival in hydrothermal vent environments.