Circular RNAs in microalgae: Uncovering their biological significance

Circular RNAs (circRNAs) have recently garnered significant attention due to their emerging regulatory roles across eukaryotic organisms. These non-coding RNA molecules are generated through a non-canonical back-splicing mechanism that covalently joins the 5' and 3' ends, resulting in a closed-loop structure. Although the complete functional landscape of circRNAs remains to be elucidated, advances in RNA sequencing technologies and computational biology have accelerated their identification and functional annotation in both plant and mammalian systems. CircRNAs are increasingly implicated in the regulation of key cellular and metabolic processes, including transcription, translation, protein-protein interactions, cellular proliferation, development, and stress responses, thereby contributing to homeostasis and survival. In this study, we present a comprehensive overview of circRNA biogenesis, structural features, biological roles, and bioinformatic tools used for their prediction in eukaryotes. However, no prior studies have systematically characterized circRNAs in microalgae. To address this gap, we analyzed RNA-seq datasets from three phylogenetically distinct microalgal species (e.g., Chlamydomonas reinhardtii, Dunaliella salina, and Phaeodactylum tricornutum) using the CIRI2 pipeline to identify putative circRNAs. Our analysis revealed candidate circRNAs potentially involved in essential biological pathways, including RNA transcription regulation, mRNA splicing, translational control, chlorophyll function, cytochrome c maintenance, and various post-transcriptional and post-translational modifications. These findings offer novel insights into the regulatory landscape of circRNAs in microalgal species and lay the groundwork for future functional investigations.