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Scientists elucidate molecular mechanisms behind dinoflagellate cyst dormancy

Dinoflagellates play crucial roles in aquatic ecosystems, particularly as major contributors to harmful algal blooms. They can enter a dormant stage, known as the resting cyst stage, that allows them to survive for extended periods—up to 150 years—in marine sediments. This dormancy is essential for their annual population dynamics, blooming cycles, and geographic expansion.

Despite the ecological importance of resting cysts, the molecular mechanisms governing their dormancy, viability maintenance, and germination in natural sediments remain largely unexplored.

To better understand this process, researchers from the Institute of Oceanology, Chinese Academy of Sciences (IOCAS), in collaboration with scientists from the University of Connecticut, investigated these mechanisms. They utilized a dinoflagellate mRNA-specific spliced leader as a "hook," along with single-molecule real-time sequencing and other physiological measurements.

This study was in Science Advances on February 7.

The researchers constructed three cDNA libraries based on DinoSL from field cyst assemblages and uncovered the genetic and metabolic mechanisms involved in cyst dormancy. They found that the vast majority of genes related to major metabolic and regulatory pathways, except for those related to photosynthetic pathways, remained transcriptionally active in cyst assemblages.

Moreover, the researchers identified "active" genes and pathways crucial for maintaining the viability and germination potential of dinoflagellate resting cysts buried in marine sediments.

"The broad active metabolic landscape observed in sediment-buried cyst assemblages highlights a vital aspect of the molecular machinery required for maintaining dormancy in cysts," explained Prof. Tang Yingzhong, the study's corresponding author.

Through metatranscriptomic analyses and subsequent hypotheses, the researchers gained deeper insights by examining laboratory-induced cysts in a representative cyst-producing dinoflagellate species. They discovered that autophagy is heightened during cyst dormancy, suggesting that alternative energy generation and cellular resource recycling are essential strategies for sustaining dormancy and viability.

Additionally, the researchers found that two classical phytohormones—abscisic acid (ABA) and gibberellic acid (GA)—have antagonistic roles in regulating cyst dormancy maintenance and release. The study demonstrated that low temperature and darkness, two environmental cues typically present in marine sediments, induce opposing effects on the biosynthesis and catabolism of ABA and GA. This results in elevated levels of ABA and reduced accumulation of GA, corresponding to deep dormancy in dinoflagellate cysts in natural environments.

This research enhances the understanding of the molecular mechanisms underlying the life cycle transitions and dormancy of dinoflagellates.