Regulation of cell cycle-related gene expression by blue light and its effects on the growth and gametogenesis of Saccharina japonica gametophytes

As an economically and ecologically important seaweed inhabiting the subtidal zone, the growth and development of kelp Saccharina japonica are regulated by various environmental factors including blue light. However, studies on the mechanisms underlying the regulation of blue light on kelp gametophyte are still very poor. This study compared the reproductive development rate of S. japonica gametophytes under different blue light exposure durations and found blue light can promote the transition of S. japonica gametophytes from vegetative growth (cell mitosis) to gametogenesis (gamete cell differentiation), with a 12-h blue light exposure being the most efficient. To investigate the role of cell cycle-related genes during gametogenesis of S. japonica gametophytes, Cyclin, CDK, E2F/DP and RBR were first identified in S. japonica. By analyzing cis-acting elements, conserved domains, and phylogenetic relationships of the E2F/DP family, we found that the E2F/DP family had the highest number of light-responsive cis-acting elements and was well conserved in brown algae. RNA-seq data were used to reveal the expression changes of cell cycle-related genes during the gametogenesis. RT-qPCR further corroborated the expression patterns revealed by RNA-seq data, and especially the expression of gene SjRBR fluctuated significantly during the process of blue light-induced gametogenesis. Based on the expression patterns of the aforementioned cell division-related genes at different developmental stages of the gametophyte, we hypothesize that these genes may play a crucial role in regulating the vegetative growth and gametogenesis of the gametophyte. These findings will further enhance our understanding of cell fate determination in multicellular organisms and will also contribute to improving the efficiency of kelp seedling culture techniques based on gametophyte clone.