Male Apomixis: An Alternative Strategy to Synthetically Engineer Clonal Seed Formation in Plants

Apomixis is a specialized form of plant reproduction, in which clonal seeds are generated through a developmental reprogramming of the sexual pathway. Based on its ability to fixate genotypes over successive generations, apomixis is considered the holy grail for plant breeding, particularly with respect to hybrid fixation. Since apomixis has not been retrieved in major crop species, research is mainly focussed on the genetic engineering of apomixis and hence on the identification of genes that underlie its major components.

Here, we present an alternative method to genetically engineer clonal seed formation; namely ‘male apomixis’. In this process, male meiosis is converted into a mitotic division and resulting clonal pollen are used to fertilize eggs that selectively eliminate their own genome input. By this way, clonal seeds are formed without the need for apomeiotic eggs. Recent studies have shown that parent-specific genome elimination (GE) can be obtained by uniparental changes in centromeric chromatin status. We here demonstrate that male apomeiosis, on the other hand, can be obtained by the combined loss of AtSPO11-1 and JAS; two proteins essential for meiotic recombination and reductional cell division, respectively. In addition, we show that the use of these pollen in the fertilization of a GE line yields diploid plants that fully retain the genomic make-up of the original pollen donor. As such, these findings demonstrate that the combined loss of JAS and AtSPO11-1 is sufficient to confer male apomeiosis and hence provides a molecular basis for the synthetic engineering of ‘male apomixis’ in plants.