The maize Ga1-s allele confers protection against ga1 pollen in popcorn and dent corn

Authors: Moran Lauter, Adrienne; Edwards, Jode; Scott, Marvin

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2022
Publication Date: 12/2/2022
Citation: Moran Lauter, A., Edwards, J.W., Scott, M.P. 2022. The maize Ga1-s allele confers protection against ga1 pollen in popcorn and dent corn. Scientific Reports. 12. Article 20809. https://doi.org/10.1038/s41598-022-25261-8.
DOI: https://doi.org/10.1038/s41598-022-25261-8

Interpretive Summary: Puramaize is the trademark for maize hybrids that are marketed to organic corn growers and contain a genetic system called Ga1 that reduces contamination by GMO pollen. The Ga1 system has been used in popcorn for decades to reduce unwanted pollen contamination. We compared the effectiveness of the Ga1 system in Puramaize and popcorn and found that while popcorn is slightly better overall, both are highly effective at preventing unwanted pollinations compared to hybrids that do not have the Ga1 system. Differences in effectiveness were attributed to genes that modify the effect of the Ga1 system, rather than differences in the Ga1 system itself. This information is important for making regulatory decisions regarding the need for GMO testing. Currently Puramaize and Popcorn are subject to different GMO testing requirements. These data suggest that with adequate field testing during development of Puramaize hybrids, they could be subject to the same GMO testing requirements as popcorn. This would reduce the cost of production of organic corn and organic corn products.

Technical Abstract: Because corn pollen can be carried great distances by air currents, maintaining genetic purity of corn grain is challenging. The challenge is substantially reduced in popcorn, which typically carries the Ga1-s allele that prevents pollination by ga1 plants, which includes the vast majority of non-popcorn commercial maize varieties in the U.S. This allele can be transferred into dent corn varieties where it has been shown to reduce unwanted pollinations for example, pollination of organic corn by GMO varieties. The effectiveness of the Ga1-s allele in popcorn and in dent corn has never been compared. This comparison is important because the popcorn and dent corn are regulated differently with regard to GMO contamination. We compared the degree of pollen exclusion of six commercial popcorn hybrids, six Ga1-s dent corn hybrids and four normal dent corn hybrids in a replicated field trial for their ability to exclude ga1 pollen using an extremely sensitive field-based assay for contamination of unwanted pollen. While both popcorn and Ga1-s dent corn had significantly better pollen exclusion than normal dent corn, popcorn had significantly better pollen exclusion than Ga1-s dent corn. Significant variation in pollen exclusion among hybrids suggests that careful screening may allow identification of Ga1-s hybrids with pollen exclusion comparable to that of popcorn. Examination of DNA sequences did not reveal any sequence differences among the Ga1-s alleles used in this study, suggesting that variation in pollen exclusion is influenced by the presence of modifier genes, rather than variation in Ga1-s alleles. The information in this study will support the development of gene purity regulations based on the ability to exclude unwanted pollen, potentially decreasing regulatory costs and increasing genetic purity of organic corn.