The identification of three novel genes involved in the rapid-growth regulation in a marine diatom, Skeletonema costatum.

In order to understand the molecular mechanism of growth regulation in phytoplankton and to develop novel growth-status indicators, a subtraction cDNA library was constructed by using the mRNA extracted from Skeletonema costatum in the rapid-growth stage (RG stage), and three RG-stage-related cDNA fragments, RG#14, RG#25, and RG#42, were obtained. According to the results of sequence analysis, RG#42 belonged to the MCM2-7 protein family, and the other two fragments, RG#14 and RG#25, were novel molecules. Under continuous illumination, these RG-stage-related mRNA expression levels increased from 100- (RG#14 and RG#42) to 1,000-fold (RG#25) with increasing growth rate. Furthermore, under a diel rhythm of light (light-dark = 12:12 h), the daily mean mRNA abundances of RG#14 and RG#25 in the exponential phase also differed from those in the late-stationary phase. However, such differences between these growth phases were not observed in the mRNA levels of RG#42 and PCNA. This study not only provided a new way to investigate the regulatory mechanisms of cell growth but also offered a possibility of employing these gene fragments as indicators to monitor the growth status of phytoplankton in the marine environment.