Led by Dr Natasha Yelina, the Crop Breeding Technologies Group based at the Crop Science Centre is developing novel breeding technologies in legume crops to enhance the production of new cultivars adapted to changing climatic conditions, as well as having sustainable yields. Legumes are economically and agronomically important crops in the UK and worldwide due to their proteinaceous seeds and their ability to enhance soil fertility, making them important crops in rotation and intercropping with cereals. The group works on legumes of importance to both high- and low-income countries.
The group focuses on meiosis, a cell division during sexual reproduction resulting in haploid gametes, egg and sperm. During meiosis parental chromosomes exchange parts in a process called recombination, or crossover. As a result, traits from both parents are reassorted before being passed on to offspring. This leads to new qualities in crops, such as yield, nutrient content, resilience to pests and adaptation to abiotic stresses and is the basis for selective breeding. The current challenges for researchers and crop breeders lie within the limitations of meiotic recombination. Not all characteristics are equally amenable to meiotic reassortment, which leaves up to a third of the genetic material unavailable for breeding and results in lengthy and costly breeding programmes.
Breakthroughs in the field, including the group's recent work, have identified mechanisms that control trait reassortment. The group aims to deepen mechanistic understanding of meiotic recombination control and translate the wealth of this knowledge into impactful breeding. To gain a deeper fundamental understanding of meiosis and translate this knowledge into step-changing breeding technologies in legume crops and beyond, the group is addressing the following questions:
How can we boost trait reassortment in crops?
Trait reassortment during meiosis results from crossovers which start as double-strand breaks on the genomic DNA and are repaired in a multistep process highly conserved across all eukaryotes. In plants only ~5% of meiotic double-strand breaks are repaired as crossovers, while the remaining ~95% are repaired as non-crossovers with limited impact on trait reassortment. Working in model plants, we and others have discovered crossover modifiers: pro- and anti-crossover factors that compete against each other during meiotic double-strand break repair, mismatch-repair factors, proteins that determine chromosome organisation during meiosis, epigenetic marks and chromatin. Modulating expression of crossover modifiers individually or in combinations is a way to boost crossovers and expedite crop pre-breeding because increasing the number of possible trait combinations translates into fewer generations of plants and individuals required to obtain cultivars with desired qualities. We are now working to identify best strategies to boost crossovers in legume crop pre-breeding using soybean as a model. In the longer term, we are aiming to develop these strategies into widely accessible breeding technologies.
What determines a crossover?
Despite discoveries of crossover modifiers and tremendous progress in understanding of what controls meiotic crossovers, there are two big unanswered questions in the field: i) what makes crossover ‘hotspots’ – several-kilobase-long genetic intervals where crossover frequencies are 10- to 100-fold higher than in the crossover-suppressed ‘coldspots’ and ii) how to efficiently ‘unlock’ genetic variation in crossover-suppressed heterochromatin-rich regions that in crops can harbour up to 20-30% of functional genes. We aim to address these questions by CRISPR-based engineering where we test whether targeted recruitment of pro-crossover factors to the DNA or erasure of crossover-inhibiting heterochromatin marks, can ensure crossovers. We aim to find out whether this approach can lead to de novo crossovers both in ‘hotspots’ and ‘coldspots’. We hope that in the future this knowledge can become game-changing in crop breeding allowing us to incorporate previously ‘locked’ traits into breeding programmes and to overcome linkage drag, or co-inheritance of agronomically useful and undesired traits.
Why are reproduction, meiosis and crossovers affected by temperature?
Elevated temperatures affect spermatogenesis and reduce fertility in humans, insects and plants. In crops sperm (pollen) abortion leads to yield losses. Meiosis, one of the key components contributing to fertility, and crossovers are temperature-sensitive, however, mechanisms behind this are poorly understood. Adaptation to temperature stress can occur naturally: some wild relatives of cultivated crops, for example, cowpea, maintain fertility under elevated temperatures. We hypothesize that this adaptation is, at least in part, due to adaptation of meiosis to heat and further hypothesize that temperature-sensitivity of meiosis can be modulated genetically. We are using forward genetics approaches in Arabidopsis and cowpea to identify mechanisms behind the sensitivity and adaptation of meiosis, crossovers and fertility to elevated temperatures. In the longer term we aim to use this mechanistic understanding to develop climate-smart crops.
