Method of hybrid seed production using conditional female sterility

The present invention relates to the production of hybrid seed in plants. In particular, the invention relates to a method of hybrid seed production using as one parent of the hybrid a plant transformed with a chimeric gene which when expressed in the female reproductive structures yields a protein that catalyzes the conversion of an exogenously-applied protoxin to a toxin, thereby rendering fertilization ineffective. Also included in the invention is the use of the conditional female-sterile plants in combination with conditional male-sterile plants to more efficiently produce hybrid seed, chimeric genes useful for the invention, transgenic plants comprising the chimeric genes, and novel promoters useful for expression in the female reproductive structures of a plant. The present invention provides a method for hybrid seed production comprising producing a conditional female sterile plant comprising a female-preferential promoter operably linked to a coding sequence which encodes an enzyme which catalyzes the conversion of a protoxin to a toxin, interplanting the conditional female sterile plant with a male sterile plant, applying the protoxin to the conditional female sterile plant, and producing hybrid seed. Viable seed formation is prevented on the conditional female sterile plant as a result of the conversion of the protoxin to the toxin in the female reproductive structures, and pollen production is prevented on the male sterile plant, thus allowing interplanting of the two parents of the hybrid cross in order to provide more efficient pollen transfer. Also provided are expression cassettes useful in the invention, plants transformed with the expression cassette, and novel female-preferential promoters.