The Evolution of Silicon Transport in Eukaryotes

Area of Science:

• * Evolutionary biology
• * Biogeochemistry
• * Molecular biology

Background:

• * Biosilicification, the creation of biological silica structures, is vital in many life forms and global cycles.
• * The evolutionary origins of silicon (Si) transporters, essential for this process, are not well understood.
• * Existing research points to the SIT family in diatoms and related SIT-L transporters in other organisms.

Purpose of the Study:

• * To investigate the evolutionary history of silicon transporters.
• * To identify SIT and SIT-L families across diverse eukaryotic lineages, including silicified and nonsilicified organisms.
• * To explore the evolutionary relationship between transporter structure and biosilicification.

Main Methods:

• * Bioinformatic analysis of SIT and SIT-L gene families in various eukaryotes and bacteria.
• * Phylogenetic analysis to infer evolutionary relationships and structural evolution of transporters.
• * Comparative genomics to identify Lsi2-like genes in siliceous and nonsiliceous organisms.

Main Results:

• * SIT and SIT-L transporters are widespread in eukaryotes and bacteria, with SIT structures evolving multiple times independently from SIT-Ls.
• * A second transporter family, Lsi2-like genes, is also broadly distributed, with distinct groups found in plants, diatoms, sponges, and choanoflagellates.
• * Both transporter families likely play a significant role in biosilicification across diverse lineages.

Conclusions:

• * The SIT/SIT-L and Lsi2 transporter families have an ancient origin and are fundamental to eukaryotic biosilicification.
• * These transporters may have initially evolved to mitigate silicon toxicity in Precambrian oceans.
• * Reductions in oceanic silicon levels during the Phanerozoic era likely led to gene losses, shaping the distribution of these transporters today.