Functional CTR-type Cu(I) transporters in an oceanic diatom

Area of Science:

• Marine biology
• Environmental science
• Molecular biology

Background:

• Copper concentration in marine environments varies significantly, impacting phytoplankton growth.
• Understanding copper transport mechanisms is crucial for marine species' survival and homeostasis.
• Molecular mechanisms of copper transport in marine species remain largely unknown.

Purpose of the Study:

• To investigate copper-responsive genes and uptake mechanisms in the marine diatom Thalassiosira oceanica.
• To elucidate how T. oceanica acclimates to a wide range of environmentally relevant copper concentrations.
• To identify specific copper transporters involved in maintaining copper homeostasis.

Main Methods:

• Studied copper uptake rates in T. oceanica at varying copper concentrations (0.012 to 12,900 pmol Cu/L).
• Identified and characterized four putative CTR-type copper transporter genes (ToCTR1, ToCTR2, ToCTR3a, ToCTR3b) from the diatom transcriptome.
• Analyzed gene expression patterns in response to different copper levels and tested gene function in a copper transport mutant yeast model (Saccharomyces cerevisiae ctr1Δctr3Δ).

Main Results:

• Demonstrated an inducible copper uptake pathway in T. oceanica, with uptake rates increasing significantly under copper limitation.
• Identified ToCTR genes sharing conserved features with high-affinity copper(I) transporters.
• Observed upregulation of CTR genes with decreasing copper concentrations, correlating with maintained growth rates; ToCTR3a/b restored growth and enhanced copper uptake in yeast mutants.

Conclusions:

• ToCTR3a and ToCTR3b function as high-affinity copper(I) transporters in T. oceanica.
• The identified ToCTR transporters collectively enable T. oceanica to survive in copper-depleted marine environments.
• This molecular machinery allows the diatom to effectively respond to natural variations in copper availability, maintaining cellular homeostasis.