Sex and Agriculture

Zusammenfassung:

Deregulation of reproductive pathways, as induced by interspecific hybridization between sexual species, has been hypothesized as a mechanism which could induce apomictic seed production.  To test this, we have compared the transcriptomic profiles of microdissected live ovules at four developmental stages between a diploid sexual and diploid apomictic Boechera.  We sequenced over 2 million SuperSAGE tags, and identified:  (1) heterochronic tags, (2) stage-specific tags, and (3) sex-specific and apomixis-specific tags.  Corresponding gene sequences were mined from sexual and apomictic flower-derived cDNA libraries generated using 454 technology.  Most heterochronic and stage-specific tags were significantly downregulated during early apomictic ovule development, and 110 were associated with reproduction.  In contrast, most late stage-specific tags were upregulated in the apomictic ovules, the result of increased gene copy number in apomictic (hexaploid) versus sexual (triploid) endosperm.  Finally, we show that apomixis-specific gene expression is characterized by a significant overrepresentation of transcription factor activity.  As the diploid apomict analysed here is an ancient hybrid, these data support the postulated link between hybridization and asexuality, and provide a biogeographical explanation for multiple evolutionary origins of apomixis in the genus Boechera.