Karyological consequences of remote inter-species cross-hybridisations
Research on inter-species hybrids including crop plants generated new important insights into evolutionary chromosome dynamics, and novel genotypes along with the know-how for maintenance and application.
Coix lacryma-jobi. L.
In general, all living and fossilised organisms of the same eukaryotic species have the identical basic chromosome number, and all its individuals with a complete complement are euploid. Individuals with deviating chromosome numbers are aneuploid exceptions. This fundamental pattern of species-specific basic chromosome numbers has served since its discovery as a very supportive tool for describing individuals taxonomically and attributing them to appropriate infra-specific ranks as well as delimiting their species per se. However, horizontal chromosome transfer (addition, substitution, translocation) via inter-species cross-hybridisation and succeeding mechanisms that restore fertility and stabilize transmission to offspring can generate new basic numbers leading to dysploid plant species. Besides chromosomes or chromosome segments in the genetic background of a different species, supernumerary B-chromosomes have been found to contribute to significant genome size variation in several species. Plant speciation is often characterised by a process of continuous increase of the genome size, which allows for a reorganisation of the linkage group system of an enlarged genome. Because of the long timescale of these processes involved in speciation, hybridisation experiments between very remotely related genotypes can produce plant material that is suited for observing inter-genomic interactions and stress response reactions at chromosome level (e.g. linkage rearrangements). These generated genotypes simulate and condense the involved adaptive processes in a few generations almost comparable to a time-lapse observation. Data on the dynamics of organisation and behaviour of chromosomes will empower a better understanding of the evolution course including the steps toward speciation at the level of the chromosome and support the evo/devo research in the Jodrell Laboratory on selected taxa with potentially nutriceutical and pharmaceutical importance as part of Kew’s breathing planet programme.
Our research into the behaviour of chromosomes in alien genetic backgrounds is accomplished by using the B-chromosome as a model. We investigate genome-wide genetic interactions and chromosome restructuring. Remote inter-species hybridisation experiments allowed us to transfer chromosomes and chromosome segments of maize (Zea mays L.) into different varieties of common oats (Avena sativa L.). We observe this plant material for chromosome structure reshuffling, basic chromosome number changes and genome size alterations. In focusing the experiments on investigating meiotic and gametophytic chromosome behaviour by using molecular and cytogenetic methods including in situ hybridization techniques we have produced and will continue to produce further knowledge and better understanding of homologous/homoeologous relationships, and regular versus irregular behaviour of standard and supernumerary plant chromosomes in the context of reproduction biology, especially in the genetic background of an alien species. The project also includes the development of practical guidelines for efficient chromosome engineering in different plant species (e.g. Coix L.) and inter-species hybrids, seed management and worldwide distribution. The usefulness of our oat-maize chromosome addition plants has been shown by numerous international applications, including the International Whole Maize Genome Sequencing Project, physiological and molecular genetic maize research. Our chromosome addition plants have also been very helpful for widening the genetic variability of oats for improving resistance against severe pathogens and diseases aiming at ecological plant cultivation supporting conservation programmes.
Key papers published since 2006.
1. Kynast, R.G. & Riera-Lizarazu, O. (2011). Development and use of oat-maize chromosome additions and radiation hybrids. Meth. Mol. Biol. 701, 259-284
2. Kynast, R.G., Joseph, J.A., Phillips, R.L. & Rines, H.W. (2010). Metaphase I pairing of B-chromosomes of Zea mays L. in the alien genetic background of Avena sativa L. Maize Genet Coop Newsletter 84, 1-14
3. Rines, H., Phillips, R., Kynast, R., Okagaki, R., Galatowitsch, M., Huettl, P., Stec, A., Jacobs, M., Suresh, J., Porter, H. & Walch, M. (2009). Addition of individual chromosomes of maize inbreds B73 and Mo17 to oat cultivars Starter and Sun II: maize chromosome retention, transmission, and plant phenotype. Theor. Appl. Genet. 119, 1255-1264
4. Kynast, R.G., Galatowitsch, M.W., Hanson, L., Huettl, P.A., Lüpke, L., Phillips, R.L. & Rines, H.W. (2008). Maternal and paternal transmission to offspring of B-chromosomes of Zea mays L. in the alien genetic background of Avena sativa L. Maize Genet. Coop Newsletter 82, 19-21
5. Kynast, R.G., Galatowitsch, M.W., Huettl, P.A., Phillips, R.L. & Rines, H.W. (2007). Adding B-chromosomes of Zea mays L. to the genome of Avena sativa L. Maize Genet. Coop Newsletter 81, 17-19
Project partners and collaborators
Phillips, Ronald (UMN, Saint Paul, MN, USA)
Rines, Howard (UMN, Saint Paul, MN, USA)
Riera-Lizarazu, Oscar (OSU, Corvallis, OR, USA)