Inter-subfamily cybrid plants between wheat and maize, Zeawheat: production via an in vitro fertilization system, genome composition, and photosynthetic type.

Introducing genetic resources from distantly related plants is necessary to provide novel traits to crops. However, wide hybridization between wheat and other plants is limited by the elimination of non-wheat chromosomes during the development of interspecific zygotes. In this study, we produced allopolyploid wheat-maize hybrid zygotes with various gamete combinations using an in vitro fertilization system and monitored their developmental profiles. Hybrid zygotes produced by fusing a maize egg, a wheat egg, and a wheat sperm were successfully developed into fertile plants. Genome sequencing revealed that the regenerated plants were 'cytoplasmic hybrids' ('cybrids'), possessing a 'wheat' nuclear/plastid genome and a 'wheat'+'maize' mitochondrial genome. Genomic PCR on the cybrids showed stable transmission of the maize mitochondrial genome to the F2 generation, and fluorescence in situ hybridization analysis suggested the recombination of mitochondrial DNA between wheat and maize in the cells of the cybrids. CO2 compensation point and δ13C analysis suggested that the cybrids perform C3-type photosynthesis. These results demonstrate that stable wheat cybrid lines, termed Zeawheat, can be generated by fusing heterogeneous gametes in optimal combinations. This study provides novel insights into using mitochondrial genetic resources between C3 and C4 plants.