Reformation of tissue balls from tentacle explants of coral Goniopora lobata: self-organization process and response to environmental stresses.

Coral has strong regeneration ability, which has been applied for coral production and biodiversity protection via tissue ball (TB) culture. However, the architecture, morphological processes, and effects of environmental factors on TB formation have not been well investigated. In this study, we first observed TB formation from the cutting tentacle of scleractinia coral Goniopora lobata and uncovered its inner organization and architecture by confocal microscopy. We then found that the cutting tentacle TB could self-organize and reform a solid TB (sTB) in the culture media. Using chemical drug treatment and dissection manipulation approaches, we demonstrated that the mechanical forces for bending and rounding of the cutting fragments came from the epithelial cells, and the cilia of epithelial cell played indispensable roles for the rounding process. Environmental stress experiments showed that high temperature, not CO2-induced acidification, affected TB and sTB formation. However, the combination of high temperature and acidification caused additional severe effects on sTB reformation. Our studies indicate that coral TB has strong regeneration ability and therefore could serve as a new model to further explore the molecular mechanism of TB formation and the effects of environmental stresses on coral survival and regeneration.