The increasing demand for food, in the context of a changing climate and deteriorating environments, will be one of the major challenges facing society in the coming decades. To strengthen global food security plant scientists and breeding companies seek to develop new crop varieties that produce a higher yield in harsher and changing environments. However, as breeding a new variety currently takes on average 10 years, the predicted changes in food demand and climate are only several breeding cycles away. Therefore, there is an urgent need to reduce the time to produce a new crop variety. In ERC Consolidator grant SynthHotSpot, we are investigating the molecular control of meiotic recombination using the model plant Arabidopsis. We have identified the gene HEI10, which encodes a conserved meiotic ubiquitin E3 ligase, as a major regulator of crossover numbers. For example, we have found that natural genetic polymorphisms in HEI10 are strongly associated with quantitative variation in crossover frequency between Arabidopsis populations. Importantly, during this work we discovered that HEI10 is highly dosage-sensitive and introduction of additional copies of this genes more than doubled crossovers throughout the Arabidopsis chromosome arms. As HEI10 is conserved not just in plants, but in fungi and animals, this may provide a gene target to manipulate crossover numbers in diverse species. The proof of concept idea that has been developed in this work is to investigate whether increasing HEI10 copy number in bread wheat is sufficient to elevate recombination frequency and thereby accelerate breeding. Crossover frequency is particularly limiting in the extremely large, hexaploid bread wheat genome, which is one of our most important crops. Our strategy is that this platform technology will be licenced to breeding companies to be incorporated into their crop improvement strategies and programs.
As proposed we have generated mapping populations with transgenic wheat lines transformed with HEI10 transgene, using a cross between the Fielder and Chinese Spring backgrounds. Multiple HEI10 F1 plants were generated and self-fertilized to generate F2 progeny, alongside control plants. DNA was extracted from these plants and each sample was genotyped using a ‘Breeder’s Array’ of ~25,000 genetic markers. These were used to identify crossover numbers and locations in the HEI10 population compared to the control. However, counter to our expectation we did not observe significant difference in recombination levels between the transgenic HEI10 and control untransformed populations. Hence, these data do not recapitulate the effect observed in the model plant Arabidopsis thaliana. Possible reasons for this include that an insufficient degree of overexpression was achieved, which may be compounded by wheat being hexaploid and so having three HEI10 copies in wild type (compared to diploid Arabidopsis which has just a single HEI10 copy). Second, the role of HEI10 in recombination may be different in wheat due to other features, for example the large difference in genome size, meaning that HEI10 does not limit recombination in this species. Our current work to address these question is to identify additional transgenic wheat lines with greater levels of HEI10 overexpression and repeat recombination assays. Second we have transformed a diploid, dicot crop (tomato) with HEI10, which may be more easier to translate our findings in Arabidopsis into. In the course of the project we have worked with IP Pragmatics to develop a business case for our technology, which I will be presenting to a major industrial player (BASF) in November 2019 to explore potential ways to collaborate.
The work we have performed has led to progress beyond state of the art, as we now have a greater appreciation of the likely roles that genome size and ploidy play in crop species and how easily HEI10 will be found to translate from the model species Arabidopsis. My strategic aim is to develop technologies, including HEI10, that transform the way breeders combine genetic variation in crop improvement programs. Ultimately I aim that breeding is accelerated and novel crop varieties will result, which are required to meet the challenges faced by an increasing population size and climate change.
