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BTT EAGER: Controlling meiotic recombination in crops by manipulating DNA methylation

Wojciech Pawlowski; Chris Franklin; Eugenio Sanchez Moran
Cornell University
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Meiotic recombination is a process in which two parental chromosomes, one from the father and one from the mother, physically exchange parts to give rise to the next generation during sexual reproduction. Recombination is a major force behind species evolution and genetic variation, and is the basis of nearly all plant and animal breeding. These crucial events are not evenly distributed along chromosomes. In particular, in many plant species with large genomes, including most crops, recombination tends to take place near chromosome ends. In contrast, central portions of chromosomes largely lack recombination, causing a major obstacle to crop breeding. The goal of this project is to better understand how modifying DNA in the cell affects meiotic recombination in crops. Recent advances in understanding recombination suggest that the distribution of recombination events on chromosomes can be altered by reducing DNA methylation, a special, naturally occurring type of modification of DNA molecules. This project will elucidate how exactly DNA methylation affects recombination. It will also examine whether DNA methylation can be artificially controlled during reproduction to change recombination patterns, which will be very useful for plant breeding. Gaining the ability to increase recombination in low-recombination regions of chromosomes will allow breeders to create novel combinations of genes that are located in these regions, and help them produce superior crop varieties. This project is conducted in collaboration with Drs. Chris Franklin and Eugenio Sanchez-Moran at the University of Birmingham, UK, as part of the Breakthrough Technologies to Advance Crop Breeding and Functional Genomics (BTT) initiative.

Recombination is initiated by the formation of numerous programmed double-strand breaks in chromosomal DNA, a small proportion of which are processed to form crossovers. Thus, the genetic variation generated by a single round of meiotic recombination is limited. Furthermore, the distribution of crossovers in plants with large genomes, which include most crops, is highly biased towards chromosomes ends. Extensive interstitial and centromere-proximal chromosome regions rarely recombine. Yet, these large genome areas contain roughly one-fifth of the genes in maize and even larger gene fractions in some other crops, which presents a serious impediment to plant breeding. Recent studies indicate that DNA methylation is a critical factor controlling which double-strand breaks become the sites of crossovers, thus shaping crossover landscape. However, the exact relationship between recombination and DNA methylation is not understood. This project seeks to elucidate how DNA methylation affects recombination patterns at the mechanistic level and lay foundations for methods to control crossover landscapes in crops by altering DNA methylation. To elucidate the effect of DNA methylation on meiotic recombination, a protocol to transiently alter DNA methylation patterns in meiosis using DNA methylation inhibitors will be developed. Chemically demethylated plants and selected mutants defective in DNA methylation will be used to determine which steps and processes of meiosis are altered by DNA methylation. The study will be conducted in maize and Brassica rapa, to explore the behavior of both monocot and dicot genomes.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Funding Source
United States Nat'l. Science Fndn.
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Sanitation and Quality Standards