Project Number: 3096-21000-021-011-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Dec 1, 2021
End Date: Nov 30, 2025
The objective is to develop a two-line hybrid breeding system using a nuclear male sterile mutant, ms8, and it's corresponding WT gene.
We have isolated a stable nuclear male sterile mutant (ms8), identified the gene, and developed a novel transgenic approach to produce 100% male sterile seeds. This new technology can circumvent the need for breeding male sterile (A)/Maintainer (B) pair or the Restorer (R) lines and create hybrids between any two lines, rather than limited to between A/B pair and R lines as in the conventional three-line breeding system. The greatest challenge to developing two-line breeding systems using nuclear male sterile mutant is to produce 100% male sterile plants because the heterozygous plant produces ¼ male sterile and ¾ fertile plants. All current strategies to develop two-line breeding system are based on rescuing the male sterility with a transgene followed by seed sorting to remove seeds containing the transgene (An et. al. 2020, PANS 117:23499). In large-scale seed production, seed sorting can’t guarantee the complete removal of the seeds with transgene, which can be a major regulatory concern for the two-line breeding systems. Our method is far superior in that we can produce 100% male sterile plants free of transgene without seed sorting. We will create a bridge plant that is homozygous for the ms8 mutation but hemizygous for the transgene construct. The transgene construct carries the wild Ms8 gene driven by its native promoter and the cytotoxic Barnase gene driven by a late-stage pollen-specific gene promoter. The wild type Ms8 gene will rescue the male sterility of the bridge plant, and the Barnase gene will kill the pollen with the transgene, leaving only pollens with the ms8 mutation. These pollens will be used to pollinate the plants homozygous for the ms8 mutation, producing seeds that are 100% male sterile and are free of the transgene. These pure ms8 seeds can be used as a female parent to produce hybrids with any other sorghum lines to produce a wide range of hybrids.