Diatom plastids depend on nucleotide import from the cytosol

Area of Science:

• Marine biology
• Cell biology
• Biochemistry

Background:

• Diatoms possess complex plastids due to secondary endosymbiosis, differing from primary plastids in metabolic pathway distribution.
• Unlike higher plants, diatoms lack plastid nucleotide biosynthesis, necessitating external nucleotide import into the organelle.
• The mechanism for nucleotide entry into diatom plastids remains largely unknown.

Purpose of the Study:

• To identify and characterize nucleotide transporters (NTTs) responsible for nucleotide import into diatom plastids.
• To elucidate the function and localization of specific NTT isoforms in diatoms.

Main Methods:

• Bioinformatic analysis to identify putative nucleotide transporters (NTTs) in diatom genomes (Thalassiosira pseudonana, Phaeodactylum tricornutum).
• Green Fluorescent Protein (GFP)-based localization studies to determine NTT targeting within the plastid.
• Heterologous expression and functional characterization of identified NTT isoforms (NTT1, NTT2).

Main Results:

• A significant number of putative NTTs were identified in diatoms.
• NTT1 and NTT2 were localized to diatom plastid membranes, with NTT1 potentially entering via the stroma.
• NTT1 functions as a proton-dependent adenine nucleotide importer, while NTT2 mediates counter-exchange of nucleoside triphosphates.

Conclusions:

• Diatoms possess a specialized nucleotide transport system involving NTTs.
• NTT1 and NTT2 are crucial for supplying nucleotides to the complex diatom plastid.
• The identified NTTs share functional similarities with those in bacteria, not primary plastid transporters.