Dr James Higgins and Professor Ed Louis
Wheat accounts for 20% of the calories and protein consumed by humans and is the largest crop in the UK, but yields have plateaued and are susceptible to decline due to extreme weather conditions. Wheat breeding is a numbers game; the more crosses generated, the greater the chance of generating useful trait combinations. However, breeding is dependent on the frequency and distribution of crossovers (CO) that are few in number (1-3 per chromosome pair) and skewed towards the chromosome ends, so even with a large number of crosses, desired combinations may not be attained. CO initiation sites are not limited in the genome by location or number, but only ~2% mature into COs, suggesting potential within the system to increase recombination.
In humans, mutations in the RECQ genes, Bloom’s syndrome helicase (BLM) and Werner’s helicase (WRN) are associated with premature ageing and early onset of cancer. RECQs are conserved throughout eukaryotes and repair DNA by homologous recombination. In Arabidopsis thaliana, the BLM orthologues (RECQ4a/RECQ4b) function redundantly as anti-recombinases during meiosis. Arabidopsis does not contain a WRN ortholog, but we have recently identified one in wheat (RECQ7), that is a pro-CO factor. RECQ4 is an anti-CO factor, so the two proteins may function antagonistically in processing DNA recombination intermediates. In wheat we have isolated knockout mutants of RECQ4 and RECQ7 as well as generating RECQ7 overexpression lines that require analysis for altered recombination patterns. We will use state-of-the-art super-resolution fluorescence microscopy in conjunction with immunolocalisation and a panel of antibodies developed in the lab that target specific proteins in the CO pathway. Using this approach we will be able to determine the spatio-temporal dynamics of recombination protein loading on meiotic chromosomes. Molecular markers will also be utilised to monitor recombination frequency. To gain a fundamental insight into the function of the RECQ helicases, budding yeast will also be employed as a model organism to determine the effect on recombination of RECQ4 and RECQ7 across two different kingdoms. Budding yeast possesses a RECQ4 ortholog (SGS1), but not a RECQ7 ortholog, similarly to Arabidopsis, which may reflect genome size, chromosome structure or chromatin environment. There are three outstanding questions that will be investigated in this PhD project:
Q1. How does RECQ7 function as a pro-recombinase in homologous DNA repair?
Q2. Does RECQ4 act as an anti-recombinase during meiosis in wheat?
Q3. Can we determine an antagonistic mechanism of action between RECQ4 and RECQ7 using both wheat and budding yeast?
The project will be directly translated into crops as well as providing fundamental knowledge on homologous DNA repair mechanisms in eukaryotes. You will be trained in all modern techniques in an active research lab, with the opportunity for training in external collaborative labs.