Hibberd Group: The evolution of C4 photosynthesis gene expression
Supervisor
Professor Julian Hibberd
Brief Summary
This project aims to test whether the MYC-MYB module that generates bundle sheath preferential expression in the C3 model Arabidopsis thaliana is conserved in the C4 species G. gynandra and whether it is responsible for driving bundle sheath preferential expression of C4 genes.
Project Summary
C4 photosynthesis arose after evolution altered the expression of genes encoding enzymes already found in ancestral C3 species (Hibberd and Covshoff, 2010). This involved both boosting expression levels and restricting expression to either mesophyll or bundle sheath cells. The spatial partitioning of photosynthesis allowed plants to generate an increased concentration of CO2 around RuBisCO to largely avoid the wasteful process of photorespiration, and under warm, dry conditions allowing C4 plants to be amongst the most efficient on the planet (Sage et al., 2011). As a consequence of this it has been proposed that engineering the C4 pathway into C3 crops such as rice could lead to increased yields (Hibberd et al. 2008; von Caemmerer et al. 2012). However, many of the mechanisms underlying these changes in gene expression are still not well understood.
The C4 pathway appears to have evolved repeatedly from the ancestral C3 state by co-opting existing molecular mechanisms from C3 leaves (Reyna-Llorens & Hibberd 2017). We recently identified a mechanism controlling bundle sheath preferential expression in C3 Arabidopsis (Dickinson, Kneřova et al., 2020) that involves MYC and MYB transcription factors (TFs) binding to closely spaced TF binding motifs to generate bundle sheath preferential expression. Orthologs of the transcription factors responsible are present in the closest C4 relative to Arabidopsis, Gynandropsis gynandra, and multiple bundle sheath preferential C4 genes have closely spaced MYC and MYB TF binding sites in their promoters. However, we do not know whether this mechanism is involved in generating the bundle sheath preferential expression of these C4 genes in G. gynandra. This project aims to test whether the MYC-MYB module that generates bundle sheath preferential expression in Arabidopsis is conserved in the C4 species G. gynandra and whether it is responsible for driving bundle sheath preferential expression of C4 genes.
What will the successful application do?
Use of bioinformatic tools to identify closely spaced MYC and MYB binding sites in the promoters of bundle sheath preferential candidate genes from G. gynandra. Use reporter genes as well as gene editing to test these promoters. Transiently express constructs in G. gynandra to test whether regions of promoters containing MYC and MYB motifs are responsible for driving bundle sheath preferential expression. Undertake stable transformation of both A. thaliana and G. gynandra, to allow more detailed insight into their regulatory characteristics. Develop a strategy to identify other transcription factors that control mesophyll of bundle sheath expression in leaves. Develop skills associated with project management and independence.