Diurnal variations in expression of photosynthesis-related proteins in the harmful Raphidophyceae Chattonella marina var. antiqua

Many biological features of Chattonella species display diurnal oscillations, but little is known about the corresponding cellular responses at the proteome level. In the present study, we hypothesized that the abundance of certain proteins would periodically fluctuate to suit the diurnal changes of biological processes in Chattonella cells. To test this hypothesis, we undertook proteomic analysis over 7 time points covering a 24-h period in C. marina var. antiqua cells at early stationary phase (12:00, 17:00, 20:00, 24:00 on day 8, and 05:00, 08:00, 12:00 on the following day). The protein profiles of C. marina var. antiqua cells collected from the diurnal cycle shared a majority of common protein spots. However, the expression of 16 out of 124 detected spots exhibited significant differences between light and dark periods and/or over the 7 time points of the diurnal cycle. The proteins of OEE, Cyt c553, and AtpB showed significantly higher expression levels in the light period, and generally were maximally expressed during the period of 12:00–17:00. The proteins of GAPDH and RPL12 generally showed higher expression levels in the dark period, and were maximally expressed during the period of 20:00–24:00. These findings support our hypothesis, and suggest that the periodic expressions of these proteins may be critical either for optimal cell utilization of resources or to maintain proper cell function throughout diurnal cycles.