Chan:Research

Chan Lab

Department of Plant Biology at UC Davis

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Centromeres: Controllers of Inheritance We study the fundamental biology of genetic inheritance, and aim to manipulate it for practical benefit. Centromeres control chromosome segregation during cell division, because they are the loci at which chromosomes attach to spindle microtubules via the kinetochore protein complex. Centromere DNA in most plants and animals consists of megabases of simple tandem repeats. These sequences can be dispensable for centromere function. Instead, the centromere is epigenetically specified by CENH3, a centromere-specific histone H3 variant that replaces conventional H3 in centromeric nucleosomes, and is essential for recruiting other kinetochore proteins. The plant Arabidopsis thaliana is ideal for studying chromosome segregation, because it combines facile genetics and cytology with large centromeres that are similar to those vertebrate cells (by contrast, laboratory yeasts have very small centromeres). We have discovered that centromere differences between two parents can cause massive chromosome segregation errors when their genomes meet in the fertilized zygote. In extreme cases, a large fraction of viable progeny are haploids containing only chromosomes from their wild-type parent. When Arabidopsis plants expressing altered CENH3 proteins are crossed to wild type, chromosomes from the mutant parent are eliminated, yielding haploid progeny. 3) Engineering centromeres to produce haploid plants Haploid plants that are converted back into diploids can greatly accelerate plant breeding. Such “doubled haploids” produce instant homozygous lines from heterozygous F1s, a process that normally takes 8-10 generations of inbreeding. We have discovered a simple method for producing haploid plants through seed by manipulating CENH3. Haploids are easily converted to diploids, so Arabidopsis geneticists can produce large populations of plants with chromosomes from only one parent. We have written a detailed protocol that describes how to produce Arabidopsis haploid plants, available at http://tinyurl.com/ArabidopsisHaploidProtocol Our method has key advantages over current procedures that often require tissue culture and are limited to specific species or genotypes. As CENH3 is found in all eukaryotes, the procedure should theoretically work in any plant species. To learn more about our technology, please see this website. Chromosome spread from metaphase II of meiosis photographed by Ravi. DNA is stained with DAPI, and five pairs of sister chromatids can be seen on either side of the meiocyte (cytokinesis in Arabidopsis is delayed until after meiosis II).