Differential expression of silicon transporter genes in frustule formation of the marine diatom Thalassiosira eccentrica LIMS-PS-3165

Abstract

Diatoms are photosynthetic unicellular organisms surrounded by silica-based cell walls known as frustules. Given their widespread distribution in aquatic systems and their prolific nature, diatoms play a pivotal role in global silica cycling. Silicon transporter (SIT) proteins play a critical role in this process by facilitating the import and intracellular transport of dissolved silica. Therefore, it is important to understand the mechanisms controlling the uptake and utilization of silica below the concentration range of Si, where free diffusion of Si is insufficient for proliferation. In our investigation, we observed varied frustule synthesis responses of Thalassiosira eccentrica LIMS-PS-3165 under different nutrient limitations through fluorescence labeling of newly synthesized frustules. Additionally, we examined the expression patterns of SIT genes following silicon replenishment and analyzed the sequences of two SITs, TeSIT1/2 and TeSIT3, from T. eccentrica. Upon silicon resupply after a period of silicon deprivation, TeSIT1/2 transcription was downregulated, whereas TeSIT3 expression remained unaffected. Analysis of the predicted amino acid sequences revealed that TeSIT1/2 and TeSIT3 share 10 transmembrane domains and two conserved GXQ motifs, indicating structural similarities and differences in their silicon transport mechanisms. These findings enhance our understanding of silicon transport responses in T. eccentrica under nutrient-limited conditions and contribute to broader knowledge of silica biogeochemistry in diatoms.