Genes for the Regulation of Sex Differentiation and Male Fertility in Mercurialis annua L.

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Abstract
The sex determination of Mercurialis annua L. (2n = 16) was analyzed. Three genes—A1B1, and B2—control reproductive organogenesis. Maleness is induced by two complementary genes: A and one of the B genes. Male strength, which is expressed by sensitivity to “feminizing” cytokinin phytohormones, is controlled by the B genes: B1 associated with B2 induces resistance, dominant B1 induces intermediate sensitivity, and B2 alone induces high sensitivity. A or both recessive B genes induce femaleness. A “sex series” of purified homozygous or heterozygous genotypes for these genes was constructed. Twelve genotypes that induce total stamen sterility, semisterility, and restored fertility also were constructed. They are homozygous dominant or recessive for the sterility inducer gene / or for the fertility restorer genes:R1 alone induces partial restoration, R1 and R2 restore total fertility, and R2 alone is inactive. These genes act in sensitive S cytoplasm. Constructed female genotypes carrying these determinants were easily masculinized by auxins. Physiological and genetic data showed that both systems interact. Femaleness and various degrees of sterility were induced by cytokinins, and maleness by auxins. I propose that these genes control the phytohormone balances that induce these phenotypes and use these strains to test the hypothesis. Comparisons with other systems of sex determination are discussed.

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