[Research advances in communication interactions among the symbionts of "bacteria-zooxanthellae-coral"]

"Bacteria-zooxanthellae-coral" is a pair of typical triangular relationships in the marine ecosystem. There are complex flows of material, information, and energy in this system. The balance and stability of the symbionts is an important guarantee for maintaining the health of coral reef ecosystems. Many studies have been conducted on the interaction of coral symbionts in the past 20 years, which help clarify the material metabolism and nutrient exchange between "bacteria-zooxanthellae-coral" and their interaction with the environment. Due to the complexity of this symbiotic system, the mechanisms of some phenomena are still not well understood, especially for the communication among the symbionts. The interaction mediated by signal molecules is the internal driving force for the homeostatic maintenance and efficient operation of coral symbionts. In this review, we tried to summarize the latest research progress by focusing on the chemical signaling molecules in coral symbiotic system, including the communications between the bacteria and bacteria, bacteria and corals, bacteria and zooxanthellae, and zooxanthellae and corals. The main signals molecules include quorum sensing (QS) molecules, dimethylsulfoniopropionate (DMSP), glycans signals, lipid signals, and the noncoding RNAs. We focused on the functional mode and ecological significance of signal molecules in symbionts, and selectively exemplified microbial cooperation and competition mediated by QS signals, the interaction between bacteria and corals under the regulation of DMSP, and the response process of corals and zooxanthellae to noncoding RNAs under environmental stresses. We proposed the future research focus and possible directions, including the expansion of research dimensions, the application of new technologies and new methods, and the construction of ecological models. This work would help improve the understanding of interactions between "bacteria-zooxanthellae-coral". The exploration about the ways based on communication language would provide new ideas for the restoration and protection of coral reef ecosystems.