Potential Impact of Apomixis on Crop Production and Food Security.

Asexual reproduction through seeds simply defines apomixis.  Apomixis is a reproductive process that occurs naturally in over 400 species but not in any major crop plants.  Attempts to introgress apomixis from wild relatives into crop species have faced obstacles such as ploidy barriers, linkage drag, and negative effects on seed set.  Nevertheless, materials generated through these attempts have been invaluable for achieving a better understanding of this reproductive phenomenon and identifying candidate genes for components of apomixis that may be engineered to synthesize apomixis in crops in the future.  Evidence for a candidate gene for parthenogenesis recently was generated.  A BABY BOOM-like (BBML) gene from the Apospory Specific Genomic Region (ASGR) of Pennisetum squamulatum was identified from sequenced bacterial artificial chromosome clones that contained markers linked to the ASGR.  The gene is predicted to encode an AP2-domain-containing transcription factor.  Similar genes from other species have been shown to play a role in cell proliferation, particularly during embryogenesis.  When transformed into sexual tetraploid pearl millet (P. glaucum), ASGR-BBML causes egg cells to develop into embryos in the absence of fertilization.  Parthenogenesis of reduced eggs has led to the recovery of dihaploid progeny from tetraploid pearl millet.  When properly regulated, this gene can be used to promote embryo development from reduced or unreduced eggs, processes with utility for doubled haploid breeding or clonal reproduction through apomixis, respectively.  Either process could facilitate breeding for improved varieties while the latter would improve access to hybrids in developing countries given their ability, as apomicts, to breed true.