The Evolutionary Pathways of the Circadian Rhythms through Phylogenetical Analysis of Basal Circadian Genes

Abstract

Circadian rhythm is the endogenous clock in organisms that regulates the performance of various physiological and metabolic events in accordance with the periodic oscillating changes in the environment, especially the periodic light-dark cycle. The clock has endowed organisms with the ability in anticipating environmental changes allowing them to adjust their survival strategies accordingly, promoting their selective fitness. However, the evolutionary path and the emergence of such an intricate and vital system remain elusive. The article aims to analyse the molecular architecture and components of the circadian clock among three kingdoms of plants, animals, fungi, and their unicellular ancestors, revealing the possible emergence of the circadian clock from the primordial circadian rhythm of prokaryotes to complicated rhythms seen in multicellular organisms. In comparative genetic analyses of the circadian clocks, researchers have identified homologs in the circadian genes of multicellular organisms with their unicellular ancestors, indicating prior emergence of the circadian clock than multicellularity. In addition, comparative genetic studies among fungi, animal, and plant circadian clocks implied that the emergence of circadian rhythms across the kingdoms resulted from convergent evolution due to the significant selective advantages concomitant with the circadian clock. Furthermore, the article also reviewed methods of gene transferring laterally, including horizontal gene transfer and endosymbiotic gene transfer, which may explain the overall similarities in the transcription-translation feedback mechanism among the many circadian rhythms. However, while genetic transfer among distantly related organisms enhanced biodiversity and biological innovations in nature, whether the horizontal changes of genetic materials contribute to the similar feedback loop of the circadian clock still requires further research to determine.