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Title: Genomic localization of the maize cross-incompatibility gene, Gametophyte factor 1 (ga1)

item Bloom, Josie
item Holland, Jim - Jim

Submitted to: Maydica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2012
Publication Date: 2/25/2012
Citation: Bloom, J.C., Holland, J.B. 2012. Genomic localization of the maize cross-incompatibility gene, Gametophyte factor 1 (ga1). Maydica. 56:1782.

Interpretive Summary: Gametophyte factors are naturally occurring genes in maize that can be used to prevent pollination of special varieties by other types of corn. Currently, most popcorn varieties have a gene called Ga1 that prevents them from being pollinated by dent corn. Thus, a farmer can grow popcorn in a field adjacent to dent corn and still produce a pure crop of popcorn. Organic corn growers are interested in using these genes to isolate organic corn production fields from nearby transgenic corn hybrids. In this study we genetically mapped the chromosomal location of Ga1. Using the genome sequence of maize and other modern maize genomics tools, we were able to pinpoint a region on chromosome 4 that contains 13 genes, one of which is expected to be Ga1. Further high-resolution genetic analysis is required to determine which of the 13 genes is Ga1. Knowing the sequence containing Ga1 will help breeders to use marker-aided selection to incorporate Ga1 into different varieties.

Technical Abstract: Gametophyte factors in maize (Zea mays L.) mediate pollen-pistil interactions that confer preferential fertilization of some pistil genotypes by pollen carrying compatible alleles. Non-Mendelian segregation ratios caused by gametophyte factors have been observed in maize since the early 1920’s. In this study, we mapped the ga1 locus by analyzing segregation distortion and QTL for seed set in recombinant inbred lines from the cross B73 × Hp301. High density genotyping-by-sequencing markers were used to delineate the position of ga1 to a 2.6 Mbp region of the B73 reference sequence (AGP version 2). We also mapped ga1 based on its inheritance in backcross generations between W22 (ga1) and a near-isogenic line carrying ga1 on a chromosome segment introgressed from a popcorn variety. The chromosome blocks introgressed from popcorn into W22 were identified with a high-density SNP assay. We created simple sequence repeat markers targeting sequences linked to ga1 to track its inheritance in the W22 backcross populations. Recently, other researchers independently mapped ga1 in crosses of Chinese dent and popcorn lines, and we compared our results to theirs with reference to the B73 reference sequence. All lines of evidence were consistent, with the intervals containing ga1 among all studies overlapping in a 2.2 Mbp interval on chromosome 4 containing 13 predicted genes.