IDENTIFICATION OF A 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID SYNTHASE GENE LINKED TO THE FEMALE (F) LOCUS THAT ENHANCES FEMALE SEX EXPRESSION IN CUCUMBER

Sex determination in cucumber (Cucumis sativus L.) is controlled large ly by three genes: F, m, and a. The F and m loci interact to produce m onoecious (M_f_) or gynoecious (M_F_) sex phenotypes. Ethylene and fac tors that induce ethylene biosynthesis, such as 1-aminocyclopropane-1- carboxylate (ACC) and auxin, also enhance female sex expression. A gen omic sequence (CS-ACS1) encoding ACC synthase was amplified from genom ic DNA by a polymerase chain reaction using degenerate oligonucleotide primers. Expression of CS-ACS1 is induced by auxin, but not by ACC, i n wounded and intact shoot apices. Southern blot hybridization analysi s of near-isogenic gynoecious (MMFF) and monoecious (MMff) lines deriv ed from diverse genetic backgrounds revealed the existence of an addit ional ACC synthase (CS-ACS1G) genomic sequence in the gynoecious lines . Sex phenotype analysis of a segregating F-2 population detected a 10 0% correlation between the CS-ACS1G marker and the presence of the F l ocus. The CS-ACS1G gene is located in linkage group B coincident with the F locus, and in the population tested there was no recombination b etween the CS-ACS1G gene and the F locus. Collectively, these data sug gest that CS-ACS1G is closely linked to the F locus and may play a piv otal role in the determination of sex in cucumber flowers.