Abstract
An analysis of the expression and activity of silicon transporters (SITs) was done on synchronously growing cultures of the diatom Thalassiosira pseudonana to provide insight into the role these proteins play in cellular silicon metabolism during the cell cycle. The first SIT-specific polyclonal peptide antibody was generated and used in the immunoblot analysis of whole-cell protein lysates to monitor SIT protein levels during synchronized progression through the cell cycle. Peaks in SIT protein levels correlated with active periods of silica incorporation into cell wall substructures. Quantitative real-time PCR on each of the three distinct SIT genes (TpSIT1, TpSIT2, and TpSIT3) showed that mRNA levels for the most highly expressed SIT genes peaked during the S phase of the cell cycle, a period prior to maximal silicon uptake and during which cell wall silicification does not occur. Variations in protein and mRNA levels did not correlate, suggesting that a significant regulatory step of SITs is at the translational or posttranslational level. Surge uptake rates also did not correlate with SIT protein levels, suggesting that SIT activity is internally controlled by the rate of silica incorporation. This is the first study to characterize SIT mRNA and protein expression and cellular uptake kinetics during the course of the cell cycle and cell wall synthesis, and it provides novel insight into SIT regulation.
Highlights
Silicon is an important element in biology, from bacteria to humans [7]
SITs were first identified in the late 1990s [32, 34], but until now, tools for an in-depth characterization of protein, mRNA, and uptake activities during the cell cycle were not available
Biochemical, molecular, and physiological tools were used to characterize the patterns of SIT protein and mRNA expression and relate that information to silicon uptake activity
Summary
Silicon is an important element in biology, from bacteria to humans [7]. The hydrated form of silicon, called silicic acid, is considered an important nutrient for plant growth [23, 54], and silica, the polymerized form of silicon, is used by certain plants for rigidity, fungal resistance, and defense against grazers. One of the largest groups of silicifying organisms is diatoms, unicellular, eukaryotic phytoplankton that use silica as a cell wall material. These organisms are found predominantly in aquatic environments but are capable of living in soils and ice. Diatoms play a dominant role in silicon biogeochemistry [49, 63], and because they are estimated to contribute 20% of global primary production [49], they play an important role in the global carbon cycle. Once the valve is completely formed, it is exocytosed and the daughter cells separate This intimate connection between cell wall synthesis and the cell cycle results in a tight coupling of silicon metabolism and cell division.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
