Cyclin B gene and its cell cycle-dependent differential expression in the toxic dinoflagellate Alexandrium fundyense Atama Group I/Clade I

Cell cycle regulation is the intrinsic determinant of phytoplankton population dynamics since cell division in unicellular organisms directly leads to population growth. Central in the regulatory engine are cyclin/CDK complexes. Cyclin B, which is highly accumulated during the G2 and M phases (often combined as G2M) of the cell cycle, can be a growth rate marker useful for harmful algal bloom research. In this study, we isolated the full-length cDNA of a cyclin B-like gene from the toxic dinoflagellate Alexandrium fundyense Atama Group I/Clade I (Afcyc, 1669 bp). The deduced protein sequence (AFCYC, 455 amino acids) is closest (68% similarity) to, and phylogenetically clustered with the mitotic cyclin documented in Lingulodinium polyedrum. This sequence contains two cyclin-specific domains, the destruction box and the cyclin B signature motif, verifying that it is cyclin B. Using quantitative reverse transcription PCR (RT-qPCR), we characterized the dynamics of Afcyc expression throughout the cell cycle. Afcyc transcript abundance was over 6-fold higher in the G2M phase than in other cell cycle phases, and showed a positive correlation with the percentage of cells in the G2M phase. Our results suggest (1) the mitotic cyclin-based cell cycle regulation is likely conserved in gonyaulacoid dinoflagellates; (2) Afcyc is transcriptionally regulated, and (3) Afcyc is a candidate growth marker for monitoring the growth rates of A. fundyense Atama Group I/Clade I.