Resistance to the Gal-M gametophyte factor in maize: A genetic solution to an undervalued risk

Authors: JONES, ZACHARY - North Carolina State University; GOODMAN, MAJOR - North Carolina State University; Krakowsky, Matthew

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2015
Publication Date: 7/24/2015
Citation: Jones, Z., Goodman, M., Krakowsky, M.D. 2015. Resistance to the Gal-M gametophyte factor in maize: A genetic solution to an undervalued risk. Euphytica. 206(3):785-791.

Interpretive Summary: The silks on a corn ear, the female flower on the corn plant, are pollinated by wind-carried pollen from tassels, the male flowers of the corn plant. Under normal circumstances it is not possible to selectively exclude certain types of pollen from fertilizing the silks, resulting in a need for temporal or geographic isolation if purity of seed is desired, as it is with organic and specialty type (popcorn, sweetcorn, etc.) corn production. The most commonly used system of pollen isolation in corn relies primarily on a gene known as Ga1 (gametophytic incompatibility-1), and this system prevents a plant with the dominant allele (Ga1) from being pollinated by a plant with the recessive allele (ga1), which is present in almost all US commercial field corn hybrids. This system is used in popcorn to allow for planting of popcorn and field corn in close proximity, but the system can be overcome if the field corn contains the Ga1-m allele, which is found in many commercial corn varieties in Mexico. As more “exotic” corn is introduced into US field corn breeding programs, the odds are good that the Ga1-m allele will appear in commercial field corn hybrids, allowing them to overcome the pollen barrier and pollinate popcorns and other specialty corns that were developed with the isolation barrier. Here we report on the existence of genetic factors that can prevent fertilization by pollen containing the Ga1-m allele and therefore preserve the reproductive isolation system. These factors were discovered in Mexican landraces, particularly specialty corns (sweet corns), and may just be a small sample of what is present in the collections held in germplasm banks.

Technical Abstract: Due to maize’s wind-driven pollination, non-target pollen contamination is problematic for producers and breeders. Maize gametophyte factors have long been used to produce selectively pollinating phenotypes. The use of these factors is the cornerstone of commercial popcorn production, and they are used for a large range of other purposes, including preventing contamination by genetically modified pollen in organic production. However this system is at great risk from another allele at the Gametophyte Factor 1 locus, Ga1-m, which overcomes the selectively pollinating phenotypes. To further complicate this problem, the risk posed by this allele has been under-assessed due to misinterpretation of the seminal work on the subject. Here we change the interpretation of this key study and report genetic resistance to the Ga1-m allele in maize. We found genetic resistance to the allele segregating in derived lines from four landraces, showed the resistance is heritable, and that it acts in full-strength and attenuated versions. Additionally, we have suggested the validity of evolutionary-based inquiry into our plant genetic resources, and provided some validation of this effort. Our results provide the first report of genetic resistance to pollination by the Ga1-m allele, providing an option to continue the use of genetic barriers to non-target pollination. A source of resistance to the Ga1-m allele allows research to be conducted about the allele itself, allowing for research into the possible existence of multiple versions of the allele and distribution of these. We anticipate our research will be a starting point for identification of additional sources of resistance to the Ga1-m allele, specifically in popcorn production, where it is most immediately needed to prevent pollen contamination, as well as the eventual localization and mapping of the resistance alleles. We also believe the suggestion of evolutionary-based inquiry into plant genetic resources will provide a highly effective method for identification of specific traits, but will need more extensive validation.