Partners and International Organizations
(English)
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AT, BE, CH, CZ, DE, DK, ES, FR, HU, IE, IT, NL, NO, PL, PT, RS, SK, UK
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Abstract
(English)
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Apomixis (asexual) reproduction through seeds is a fascinating developmental process with a tremendous potential for plant breeding and crop production. It leads to the formation of clonal offspring by conservation of the maternal genotype. Any complex genotypes, including high yielding F1 hybrids and potentially hybrid vigour, can be fixed over subsequent generations. Although apomixis is common in more than 400 plant species, it is not represented in major crop plants. Engineering of apomixis into crops has been attempted over the last years. However, it has proven difficult due to the limiting knowledge of the developmental programs regulating both sexual and apomictic reproduction. Apomixis and sexual reproduction are closely related. Apomixis is likely caused by a deregulation of the sexual pathway (1). During sexual reproduction, the megaspore mother cell (MMC) is the first cell of the female reproductive lineage. It is committed to meiotic fate. Typically, only one meiotic product, the functional megaspore, survives and gives rise to the mature embryo sac harbouring the two female gametes (egg cell, central cell). Embryo and endosperm development initiates after double fertilization. In apomictic species only a few key developmental steps are altered: The first cell of the apomictic germline, the apomictic initial cell (AIC), omits or aborts meiosis to give rise to an unreduced gametophyte. Subsequently the embryo develops by parthenogenesis from an unfertilized egg cell. To study the transcriptional basis underlying apomictic reproduction, we use Boechera gunnisoniana as apomictic model that is closely related to Arabidopsis thaliana. In this species endosperm development requires central cell fertilization, while embryos are formed by parthenogenesis (98%, N = 84), based on flow cytometry on individual seeds (4). As no reference genome for this species is available, we generated a reference transcriptome based on RNA isolated from microdissected ovule tissues using RNA-Seq. The assembled sequences were annotated by Blast2GO and BLAT allowing functional categorization and identification of Arabidopsis homologues (4). Cell-type specific transcriptome analysis was done by a combination of laser microdissection with microarray analysis or RNA-Seq analyses, allowing the identification of >12'000 genes each expressed in the Boechera AIC, egg and central cell. For the respective cell types of interest, transcriptome analyses were done before in Arabidopsis, allowing comparisons between sexuality and apomixis (2-3, 5). Interestingly, statistical analyses identified differential activity of a number of pathways in Boechera and Arabidopsis reproductive lineages, including cell cycle, hormonal pathways, epigenetic regulation, and transcriptional regulation. In addition, enriched activity of spermine and spermidine synthesis and certain signal transduction pathways is a feature of the apomictic as compared to the sexual germline. In summary, our study provides important new insights into the transcriptional basis underlying apomixis.
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