Protein import into secondary plastids of haptophytes

Zuzana RUSNOK

Bachelor's thesis

Import proteinů do sekundárních plastidů haptofytů

Abstract:

Protein import into the plastid is a crucial step that ensures the survival of plastid-bearing organisms. In primary plastids, proteins only need to cross two membranes to reach the plastid stroma. The situation is more complicated in secondary complex plastids, which are typically enveloped in four membranes. Such topology requires the evolution of distinct transport mechanisms and precise targeting signals to ensure reliable protein import. This thesis focuses on haptophytes, a group of marine algae possessing a red complex plastid. In recent years, many discoveries have been made regarding protein import into these plastids, including the discovery of an ERAD-derived translocon (SELMA) situated in the second outermost membrane (the periplastidial membrane). However, haptophytes have been often overlooked in these studies, and no satisfactory functional annotation of the components forming their translocation machineries is available. I collected datasets from five haptophyte representatives across all currently accepted classes and conducted a bioinformatic analysis of selected components of the translocation machineries. In this thesis, I present a functional annotation of these components, curated using various bioinformatic tools, such as TargetP, SignalP and DeepLoc. A short conserved motif, that appears to be specifically associated with proteins targeted into one of the intermembrane compartments, was noticed. It could help identify proteins specifically targeted to this space. Experimental verification of this motif's function and protein targeting could be the focus of future studies.

Abstract:

Protein import into the plastid is a crucial step that ensures the survival of plastid-bearing organisms. In primary plastids, proteins only need to cross two membranes to reach the plastid stroma. The situation is more complicated in secondary complex plastids, which are typically enveloped in four membranes. Such topology requires the evolution of distinct transport mechanisms and precise targeting signals to ensure reliable protein import. This thesis focuses on haptophytes, a group of marine algae possessing a red complex plastid. In recent years, many discoveries have been made regarding protein import into these plastids, including the discovery of an ERAD-derived translocon (SELMA) situated in the second outermost membrane (the periplastidial membrane). However, haptophytes have been often overlooked in these studies, and no satisfactory functional annotation of the components forming their translocation machineries is available. I collected datasets from five haptophyte representatives across all currently accepted classes and conducted a bioinformatic analysis of selected components of the translocation machineries. In this thesis, I present a functional annotation of these components, curated using various bioinformatic tools, such as TargetP, SignalP and DeepLoc. A short conserved motif, that appears to be specifically associated with proteins targeted into one of the intermembrane compartments, was noticed. It could help identify proteins specifically targeted to this space. Experimental verification of this motif's function and protein targeting could be the focus of future studies.

Keywords

Haptophyta, protein import, secondary plastids, functional annotation

Language used: English

Date on which the thesis was submitted / produced: 10. 5. 2026

Accessible from:: 31. 12. 2999

Thesis defence

• Date of defence: 2. 6. 2026
• Supervisor: Mgr. Vojtěch Žárský, Ph.D.

University of Ostrava

Faculty of Science

Bachelor programme / field:
Biology / Systematic Biology and Ecology