Green to the fullest: Genes controlling the total chloroplast complement of photosynthetic cells

The entire biosphere relies on photosynthesis. In plants the bulk of photosynthesis is carried in leaf mesophyll cells, the chloroplast-filled version of plant ground tissue. Mesophyll cells contain, between the central vacuole and the plasma membrane, cytoplasm filled with a single layer of chloroplasts (1). Detailed microscopic, quantitative image analysis has observed that the proportion of the “plan area” of the cell occupied by chloroplasts in mesophyll cells in a wide range of plant species is essentially constant (2). This proportion of the cellular plan area occupied by the plan area of all of its chloroplasts has been called the “cellular chloroplast index”.

We don’t know how this chloroplast set-point is achieved. We have in the past shown that mutations which cause exaggerated light responses in tomato fruit also cause this set-point to increase (4). In leaf mesophyll cells, however, first clues on the control mechanisms came from the identification of reduced chloroplast coverage (rec) mutants in Arabidopsis thaliana (3). REC1, REC2, REC3 and FRIENDLY are a family of genes, the loss of all of which results in viable, pale plants whose mesophyll cells have about 40% of the chloroplast index of the wild type. Being able to control the chloroplast index of cells at will could have major applications in a range of plant science and technologies.

We aim at identifying genes whose loss or gain can boost the chloroplast index, by searching for suppressor mutations of the pale phenotype of rec mutants in Arabidopsis. Suppressor mutant screens have been greatly productive in chloroplast biology (see 4). This project will carry out searches for both loss-of-function and gain-of-function mutations, for which we have already developed or assembled the corresponding tools. This project will carry out both genetic screens. Once relevant mutants are identified, loss-of-function genes will be cloned by next-generation mapping by sequencing, while positive regulator mutants will be cloned using standard molecular genetic techniques. The characterisation of the mutants will also involve detailed quantitative microscopic analysis, using differential interference contrast, confocal and electron microscopy, and whole metabolomics analysis, using the state-of-the-art platforms at Royal Holloway.

The ultimate aim is to then transfer this knowledge by generating corresponding mutants in a fruit crop in which the plastid cellular index plays a fundamental role in determining lipophylic antioxidant production or cell-factory potential.

ENTRY REQUIREMENTS:

We are looking for high calibre students who have a UK Bachelor Degree with at least 2:1 in a relevant subject or overseas equivalent qualification. A master’s degree in a related subject would be advantageous. The candidate should have experience of practical laboratory work as well as having successfully completed a research project. English language requirements for Postgraduate Research degrees: IELTS 6.5 overall, writing 7.0, no other subscores lower than 5.5. Please refer to the following link on how to apply: https://www.royalholloway.ac.uk/studying-here/applying/postgraduate/how-to-apply/

When applying and in all correspondence, specify the project Title, project code (BiolSci2021-ELJPDF) and mention this Find-a-PhD advert. Shortlisted candidates will be contacted by the end of May. Interviews will be held online in the first week of June or shortly thereafter. Project supervisors welcome informal project enquiries via Find-a-PhD email.