Elucidating molecular mechanisms of chloroplast biogenesis and operation: protein translocation and regulation

Plastids are a diverse family of plant organelles with numerous functions that are vital for plant growth. The family includes chloroplasts (responsible for photosynthesis), and a range of non-photosynthetic variants such as starch-containing amyloplasts in seeds, tubers and roots, carotenoid-rich chromoplasts in flowers and fruits, and chloroplast-precursor organelles in dark-grown plants called etioplasts [1]. Most plastid proteins are encoded by the nuclear genome and synthesized in the cytosol as precursors with N-terminal targeting peptides.

Import of precursors into chloroplasts is mediated by the TOC-TIC translocons [1]. Remarkably, these translocons are directly regulated by the ubiquitin-proteasome system via a process termed chloroplast-associated protein degradation (CHLORAD) [1].

We identified a ubiquitin E3 ligase in the plastid outer membrane called SP1, and showed that it targets TOC components for degradation [2]. We subsequently showed that SP1 is part of a broader system (termed CHLORAD) which incorporates a protein ‘retro translocation’ system; this extracts target proteins from chloroplasts to enable their degradation in cytosolic proteasomes [2]. By regulating protein import, CHLORAD controls the plastid’s proteome, functions and developmental fate (e.g., which plastid variant is formed) [1].

These discoveries suggested novel crop improvement strategies [3]. However, many mechanistic details of the CHLORAD pathway remain to be elucidated.

Our research is focused on the biogenesis of chloroplasts (plastids) in plants. Particular areas of interest are the import into chloroplasts of nucleus-encoded proteins, and ubiquitin-dependent proteolysis via a process called CHLORAD (chloroplast-associated protein degradation). As a DPhil student in our group, you would be part of a well-funded research team that is conducting pioneering research in these areas. Details of the project would be defined through discussions between the student and supervisor.

We seek to understand the molecular mechanisms governing chloroplast protein homeostasis in plants, focusing in particular on protein import via the TOC-TIC translocon complexes, and proteolytic regulation of these complexes by the CHLORAD system. To do this, we apply a full spectrum of molecular, cellular, genetic, biochemical, structural and bioinformatic approaches, and we study the model plant Arabidopsis thaliana as well as a range of crop species.

The exact methods and approaches that we use depends on the project and the specific questions being addressed.

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This project is part of the DPhil in Biology programme, and is not a funded course at the University of Oxford; as such, students are expected to explore options for funding. However, we anticipate being able to offer around 6 full graduate scholarships to incoming DPhil students in 2027/28.

You will be automatically considered for several Oxford scholarships, which cover fees and stipend, if you fulfil the eligibility criteria and submit your graduate application by 6 January 2026. Scholarships are awarded based on academic achievement and potential to excel as a DPhil student.

For further details about searching for funding as a graduate student visit the graduate study information on our website.

For full entry requirements and eligibility information, please see the main admissions page.