CHROMELIM

"Chromosome elimination in plant wide hybrids – explaining the phenomenon and applying lessons from a model system in Hordeum to problems of speciation, gene introgression and breeding new crop plants."

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 Obiettivo del progetto (Objective)

'Complete uniparental chromosome elimination occurs in some plant interspecific and intergeneric hybrid combinations. This phenomenon precludes viable hybrids from developing and results in haploid embryo formation of only one of the parents. It is, therefore, a major barrier for introgressing desirable traits from wild species into crop plants and breeding new crop species. We will investigate selective elimination of parental chromosomes during the development of hybrid embryos by using crosses in the genus Hordeum as a model since the degree of chromosome retention is influenced by parental genotype and environmental conditions after fertilisation. Once the crosses are made our aims are first, to establish whether a genome dosage exists to promote or retard elimination; second, to characterise the tissue-specific nature of elimination; and third, to identify which barley chromosomes are involved in elimination. We will use combined immunostaining methods and cytogenetic analyses to determine the activity and location of the highly conserved histone H3-like centromeric protein A (CENH3), which acts as a regulator of the mitosis-dependent elimination process. The knowledge gained should result in immense benefits accruing to agriculture by allowing the prediction of suitable crosses for either haploid or hybrid plants, both of which can be used in practical plant breeding programmes. Furthemore, we will make a huge step forward in our understanding of the interaction of parental genomes in newly-formed hybrids to provide valuable new insights into species evolution.'

Introduzione (Teaser)

Developing new improved varieties of crop from different species or genera is one way of introducing desirable traits from wild relatives. However, the process is sometimes hindered by complete elimination of the chromosome complement of one of the parent strains.

Descrizione progetto (Article)

To capitalise on the genetic products of evolution for survival, the Chromelim project investigated selective elimination of parental chromosomes during the development of hybrid embryos. The team used crosses with Hordeum, a genus that includes commercially grown barley, and Hordeum vulgare (H. vulgare) as well as about 30 species of grasses native to temperate regions.

Project scientists assessed the effects of variables such as parental genotype and temperature on chromosome stability and chromatin properties. To do this, they bred hybrids from wild representatives H. bulbosum and H. marinum.

Chromelim scientists found that unlike H. vulgare and H. bulbosum hybrid embryos, there was no effect due to temperature on chromosome elimination or retention. When analysed according to genomic in situ hybridisation, all seven chromosomes from each parent were present.

At the molecular level, the highly conserved histone H3-like centromeric protein A (CENH3) acts as a regulator of the mitosis-dependent elimination process. The scientists looked at the chromosomes using indirect immunostaining at the 2C stage of cell division, when there are representatives of both parental chromosome groups but they have not yet replicated.

Determining the precise activity and location of CENH3 would be a major breakthrough in plant breeding. Chromelim researchers found that in this wild hybrid, there was no major reorganisation of the activity of this key protein.

Hybridisation of crops frequently results in loss of the 'nuts and bolts' genes that confer immunity to disease in wild ancestors. Being able to reintroduce these traits would be a major advantage in the plant breeding sector.