A novel hybrid seed production technology based on a unilateral cross-incompatibility gene in maize

Hybrid seed production technology (SPT) using genic recessive male sterility is of great importance in maize breeding. Here, we report a novel SPT based on a maize unilateral cross-incompatibility gene ZmGa1F with an extremely low transgene transmission rate (TTR). Proper pollen-specific ZmGa1F expression severely inhibits pollen tube growth leading to no fertilization. The maintainer line harbors a transgene cassette in an ipe1 male sterile background containing IPE1 to restore ipe1 male fertility, ZmGa1F to prevent transgenic pollen escape, the red fluorescence protein encoding gene DsRed2 for the separation of male sterile and fertile seeds, and the herbicide-resistant gene Bar for transgenic plant selection. When the maintainer line is selfed, gametes of ipe1/transgene and ipe1/- genotypes are produced, and pollen of the ipe1/transgene genotype is not able to fertilize female gametes due to pollen tube growth inhibition by ZmGa1F. Subsequently, seeds of ipe1/ipe1 and ipe1/transgene genotypes are produced at a 1:1 ratio and could be separated easily by fluorescence-based seed sorting. Not a single seed emitting fluorescence is detected in more than 200,000 seeds examined demonstrating that the pollen-tube-inhibition (PTI)-based TTR is lower than what has been reported for similar technologies to date. This PTI-based SPT shows promising potential for future maize hybrid seed production.