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Professor Julian Hibberd


Brief Summary

We discovered that Myb-related transcription factors (Du et al., 2013) play a previously unknown role in chloroplast development. This project aims to elucidate the underlying molecular mechanism and test the extend of its conservation during land plant evolution.


Project Summary

Chloroplasts, the site of photosynthesis in plant cells, are fundamental to life on the planet. Chloroplasts originated from an endosymbiotic event between a cyanobacterium and an eukaryotic cell over one billion years ago. The endosymbiotic cyanobacterium progressively lost independence and as a consequence multiple genes that allow chloroplast biogenesis are now encoded by the nuclear genome. However, the only known transcription factors belong to the Golden2-Like and GATA families - GATA Nitrate-inducible carbon metabolism-involved (GNC) and Cytokinin-Responsive GATA Factor 1 (CGA1) (Cackett et al., 2021; Waters et al., 2009). Importantly, mutant alleles in both GLK and CGA1/GNC possess partially functional chloroplasts indicating that there are additional unidentified players controlling chloroplast development. 

We used Marchantia as a platform to identify novel regulators of chloroplast development. In Marchantia genetic studies are made easier, compared to angiosperms, by its small gene families, lack of redundancy and a dominant haploid phase in its life cycle. Marchantia also provides a unique platform for live-tissue microscopy where chloroplast can be easily visualised and tracked. We identified a Myb-related transcription factor (TF) with a previously unknown role in chloroplast development in Marchantia. By using RNA sequencing analysis, we also identified a series of candidate genes that are potential targets of the identified Myb-related TF. Orthologs of the identified Marchantia Myb-related TF are present in all other land plant sequenced genomes examined. This observation suggests that its role in chloroplast development may be conserved in other land plants including angiosperms. 

This project aims to elucidate the mechanism underlaying chloroplast development regulation by Myb-related TFs in Marchantia and test the extent of conservation in angiosperms


What will the successful application do? 

Use CRISPR/Cas9 genome editing to generate knockout mutants to test the function of the Myb-related TF candidate targets. Characterize the phenotypes using advanced microscopy and physiological assays to elucidate the function of the genes. Assess the functional relationship between the candidates by generating double mutants, performing complementation experiments and generating gene reporter lines. Perform a forward genetic screen to identify suppressors of the MYB related pathway. Perform ChIP-sequencing analysis to identify additional targets. Develop a strategy to identify the role of orthologs in angiosperms using Arabidopsis thaliana as an experimental system and test the extent of functional conservation during land plant evolution. Develop skills associated with project management and independence.