Conditional Male Fertility in Chalcone Synthase-Deficient Petunia

Abstract

Transgenic petunia plants with suppressed chalcone synthase gene expression produce abnormal anthers devoid of flavonoid pigments. Although viable pollen is produced, pollen germination and tube growth are severely reduced both in vivo and in vitro. This results in plants that are self-sterile. Pollen from the transgenic plants is partially rescued by inbred V26 stigmas, resulting in seed set that is approximately 30% of normal. Female fertility in the transgenic petunia is unaffected by the lack of flavonoids. We propose the term conditional male fertility (CMF) to describe the state in which viable but flavonoid-deficient pollen does not function in self-crosses and is partially functional on wild-type stigmas. Although this condition has attributes of both male sterility and self-incompatibility, it is clearly different. This observation in petunia has similarities to the earlier report of Coe et al. (1981) that most pollinations made with chalcone synthase (CHS)-deficient maize pollen were unsuccessful. The possibility that normal development of the male gametophyte requires flavonoid synthesis in many or all higher plants is discussed. The dominant CHS deficiency and male sterility in petunia, taken together with the recessive CHS deficiency and male sterility in maize, suggest that flavonoid synthesis in the sporophyte rather than the gametophyte is required for fertility.