Pectin methylesterase activities in reproductive tissues of maize plants with different haplotypes of the Ga1 and Ga2 cross incompatibility systems.

Total PME activity in reproductive tissues was related to haplotypes at maize cross incompatibility loci, suggesting that these loci function by controlling PME activity. In maize, the pollination outcome depends on the haplotypes of the interacting male gametophyte (germinated pollen) and female sporophyte (silk) at several cross-incompatibility loci. Functional alleles (-S haplotypes) of the cross-incompatibility loci Ga1 and Ga2, both encode two pectin methylesterases (PMEs), one that is expressed in silk and the other in pollen.

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.