Variation in degree of pollen exclusion for ga1-s unilateral cross incompatibility in temperate maize breeding populations

Fertilization and kernel development are crucial for breeding and agronomic production of maize (Zea mays L.), which is prone to outcrossing. Because of this tendency, a major issue for organic corn farmers is to maintain genetic purity of their crop. One way to maintain this purity is to use a unilateral cross incompatibility system such as Ga1-s. However, lack of complete pollen exclusion has been reported in Ga1-s heterozygotes, complicating introgression of this trait into breeding germplasm. A systematic, quantitative evaluation of pollen exclusion rates in breeding lines would greatly facilitate use of this system. The purpose of this study is to quantitatively evaluate exogenous ga1 pollen exclusion of a diverse set of Ga1-s/ga1 F1 hybrids representing the stiff stalk and nonstiff stalk heterotic groups, and the Iowa Synthetic Corn Borer population. Differences between genotypes but not heterotic groups were observed when applying exogenous ga1 pollen onto heterozygotes possessing the same Ga1-s allele, indicating there are epistatic interactions between Ga1-s and modifier loci in the ga1 parents tested.This article is published as Boerman, Nicholas A., Adrienne N. Moran Lauter, Jode W. Edwards, and M. Paul Scott. "Variation in degree of pollen exclusion for ga1‐s unilateral cross incompatibility in temperate maize breeding populations." Agrosystems, Geosciences & Environment 4, no. 4 (2021): e20220. doi:10.1002/agg2.20220.Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted

The Ga1 locus of the genus Zea is associated with novel genome structures derived from multiple, independent nonhomologous recombination events

The Ga1 locus controls cross-incompatibility between field corn and popcorn. The Ga1-S haplotype contains 2 types of pectin methylesterase (PME) genes, ZmPme3 and several copies of ZmGa1P that are expressed in silk and pollen, respectively. The ga1 haplotype contains nonfunctional tandem repeat sequences related to ZmPme3 and ZmGa1P. This haplotype can cross-pollinate freely and is widely present in field corn. The primary objective of this study is to characterize the repeat sequences from a diverse collection of maize and teosinte lines and use this information to understand the evolution of the Ga1 locus. First, we characterized the complexity of the Ga1 genome region in high-quality maize genome assemblies that led to their categorization into 5 groups based on the number and type of PME-like sequences found at this region. Second, we studied duplication events that led to the ga1 and Ga1-S repeats using maximum likelihood phylogenetic reconstruction. Divergence estimates of the ga1 haplotype suggest that the duplication events occurred more than 600 KYA whereas those in Ga1-S occurred at 3 time points, i.e. >600, ∼260, and ∼100 KYA. These estimates suggest that the ga1 and Ga1-S tandem duplication events occurred independently. Finally, analysis of ZmPme3 and ZmGa1P homologs in Zea and Tripsacum genomes suggests that ga1 and Ga1-S repeats originated from an ancestral pair of PME genes that duplicated and diverged through 2 evolutionary branches prior to the domestication of maize.This article is published as Amruta R Bapat, Adrienne N Moran Lauter, Matthew B Hufford, Nicholas A Boerman, M Paul Scott, The Ga1 locus of the genus Zea is associated with novel genome structures derived from multiple, independent nonhomologous recombination events, G3 Genes|Genomes|Genetics, Volume 13, Issue 11, November 2023, jkad196, https://doi.org/10.1093/g3journal/jkad196.This work is written by (a) US Government employee(s) and is in the public domain in the US