Avani Dave, Jai Hind College
Dinoflagellates can be best described as a class of single-celled organisms forming a major constituent of the marine eukaryotes ecosystem that plays an essential role in aquatic primary production. That being said, several dinoflagellates are notorious for their harmful algal bloom (HAB) species, releasing high levels of marine toxins which lead to a damaged environment and undesired effects on human health. While they bring about deleterious environmental conditions for other organisms, dinoflagellates are known to successfully escape unfavourable conditions due to their cyst-forming abilities. This trait is considered to be an adaptation, allowing them to switch their inhabitation in the benthic division and in the water-current based on the conditions.
Out of the 2000 species of aquatic dinoflagellates, over 10 % form cysts during their lifespan. These cysts further help in the propagation of the species acting as a repertoire of cells. Pellicle and resting cysts are the two variants- the former having a thin cyst wall arising either sexually or asexually, and the latter having thick cyst walls arising sexually. The formation of pellicle cysts occurs naturally under stress-stimulus from the environment; this stimulus can be induced due to mechanical harm, nutritional deficiency, darkness, temperature changes, and/or infections.
Pieces of evidence from many in situ studies demonstrate that pellicle cyst production is hypothetically linked to light cycles. Considering the insufficient comprehension of the fundamentals of encystment, Guo, X., et al. conducted a study to understand the underlying molecular mechanisms that modulate cyst formation in dinoflagellates. In this study, transcriptome and metabolome analyses were carried out on pellicle cysts of Scrippsiella trochoidea induced by low temperature and darkness.
Results obtained from the study
No notable transcriptional reaction in the cyst was detected at 2 h, but observations at 5 h demonstrated tremendous reprogramming of the transcriptome and the metabolome. The gene-to-metabolite connection showed that the early stages of conversion from vegetative forms into pellicle cysts were an energy-requiring process, and brought about the activation of catabolic initiation, like glycolysis, β-oxidation, Krebs cycle, and oxidative phosphorylation, in order to deal with the stress induced by cold and darkness. That being said, after the vegetative cells were completely transformed into pellicle cysts, metabolism was highly lowered and was coupled with aggregation of sugars, PUFA, and amino acids which provided an extended survival. 56 differentially expressed genes assisting in the passage of signals were identified and showed that S. trochoidea acquired a cold-darkness stimulus. This stimulus triggered the pathways that needed in encystment. There was an increased expression of the genes that code for enzymes that mainly occurred during ROS, indicating that pellicle cysts actively respond to ROS. Along with these, the expression of many cell cycle genes was repressed, hinting towards the lack of growth. 11 DEGs related to the sexual mode of reproduction proposed that pellicle cysts or some of their components may be arising because of sexual reproduction.
Conclusion
Even though encystment is a complex mechanism, current age genetic analysis tools facilitate the elucidation of the various critical steps necessary in pellicle encystment. This study incorporated the transcriptome and metabolome analyses of pellicle cysts produced by S. trochoidea, allowing an in-depth understanding of the molecular basis of the intense cellular variations assisting in encystment. The outcome of this study has given essential insights into the expression of genes and metabolite profiles of pellicle cysts. This has laid the foundation for further delineation of pivotal regulatory genes and metabolites involved in encystment and excystment. Having a detailed comprehension of these characteristic traits makes it possible to supervise and control dinoflagellate blooms.
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Source: Guo, X., Wang, Z., Liu, L. et al. Transcriptome and metabolome analyses of cold and darkness-induced pellicle cysts of Scrippsiella trochoidea. BMC Genomics 22, 526 (2021). https://doi.org/10.1186/s12864-021-07840-7
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Author Info: Avani Dave is currently in the final year of her bachelor’s degree, majoring in Life Sciences. Holding a good academic and extra-curricular record, she is on a constant journey of acquiring exposure in her field of interest while simultaneously not limiting herself to just that. Avani likes studying Diseases and Syndromes and everything under this umbrella! That being said, she is adept at working across departments and promises to deliver.
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