EVIDENCE FOR A COMMON SEX DETERMINATION MECHANISM FOR PISTIL ABORTIONIN MAIZE AND IN ITS WILD RELATIVE TRIPSACUM

Cultivated maize (Zea mays) and several other members of the Tribe And ropogoneae produce unisexual florets. In maize, the formation of two s taminate florets in each spikelet on the tassel and a single pistillat e floret in each spikelet on the ear includes a pistil abortion proces s that requires the action of the TASSELSEED2 gene. In Eastern gamagra ss (Tripsacum dactyloides) the GYNOMONOECIOUS SEX FORM1 gene appears t o perform a similar role in pistil abortion. These genes were shown to be homeologs by restriction fragment length polymorphism mapping and by the failure of the gsf1 and ts2 alleles to complement one another i n intergeneric hybrids. Molecular analysis of the gsf1 allele shows th at it is caused by a 1.4-kb deletion mutation. Both TASSELSEEDZ and GY NOMONOECIOUS SEX FORM1 show similar expression patterns in subepiderma l cells of pistils just before abortion. These results suggest that th e formation of staminate florets in the Andropogoneae represents a mon ophyletic trait.