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HyLife Report Summary

Project ID: 339113
Funded under: FP7-IDEAS-ERC
Country: Germany

Mid-Term Report Summary - HYLIFE (Exploiting hybrids between annual and perennial plant species to identify genes conferring agronomically important traits)

Plants differ tremendously in their life span. Many species live for less than a year and reproduce only once during their life cycle, while others live for hundreds of years and reproduce every year. These different life histories are referred to respectively as annual and perennial. We are studying the genetic and molecular basis of the differences between annual and perennial plants with the aim of using this information to modify the behavior of crops. Fortunately, although there are many differences between plants exhibiting these two life histories, they can diverge relatively quickly in evolution so that closely related sister species can be annual and perennial. We have utilized this feature to perform inter-species crosses between annual and perennial species in the Arabis genus of the Brassicaceae (cabbage) family and are using the segregation of chromosomal segments in the progeny of this cross to identify genes conferring agronomically important life-history traits.
The first objective of the proposal was to make a library of plants containing defined segments of the annual Arabis montbretiana genome introgressed into the perennial Arabis alpina. High through put modern DNA sequencing approaches were used to identify which parts of the annual genome were in the perennial plant. These approaches depended on the annotated genomes of both species that we generated in the project. Interestingly, although the annual and perennial species are very closely related the perennial genome is over a 100 million base pairs larger than the annual genome, and there might be a selection for annuals to have smaller genomes. A small set of 40 lines that have inherited different chromosomal regions from the annual species has been established, and in these lines almost the whole A. montbretiana genome is present in segments in the perennial A. alpina.
The project focuses on three phenotypes associated with divergence of annual and perennial plants. These are all related to reproduction, because when the annual reproduces it forms many flowers and seeds until it dies, whereas the perennial strictly limits the extent and duration of flowering to ensure that it survives to the next year. The traits we study are variation in senescence on flowering, differences in duration of flowering and alterations in the number of branches that undergo flowering. During the genetic experiments that were necessary to construct the introgression lines, plants showing phenotypes of interest were identified. One family was identified that showed a striking difference in the duration of flowering. This line flowers after exposure to cold, as do both parents, but only forms a few flowers and then the shoot reverts to forming leaves and continues to grow vegetatively. Therefore, in this line the stability of the transition to flowering and reproduction has been disrupted and the duration of flowering is reduced. Recently using genome engineering with the CRISPR-cas9 system in the perennial species, we showed that mutations in a specific transcription factor also have this effect on the duration of flowering, and suggest that the introgressed segment of the annual genome might impair the activity of the flowering pathway containing this transcription factor. A second line of interest shows a severe delay in flowering compared to Arabis alpina. The segment of the annual genome present in this plant therefore affects the second trait of interest related to the extent of flowering and the number of branches that undergo the transition. The effect of the A. montbretiana genomic segment is clearly genetically dominant over the parental A. alpina, and we have identified in this segment two genes that are present in the annual A. montbretiana genome but have been deleted from the perennial A. alpina genome. We propose that these two genes confer this difference in flowering behavior.
Therefore, in the first period of this grant we have made progress towards understanding the genetic basis of differences between closely related annual and perennial species. By sequencing the genomes of both species we can compare their gene content and can test the functional significance of the differences we observe using introgressions of the annual genome into the perennial. These experiments are providing understanding of reproductive traits that contribute to seed yield in crop plants.

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