ANTISENSE INHIBITION OF FLAVONOID BIOSYNTHESIS IN PETUNIA ANTHERS RESULTS IN MALE-STERILITY

Inhibition of flower pigmentation in transgenic petunia plants was pre viously accomplished by expressing an antisense chalcone synthase (chs ) gene under the control of the cauliflower mosaic virus (CaMV) 35S pr omoter. This chimeric gene was not effective in inhibiting pigmentatio n in anthers, presumably because the viral CaMV 35S promoter was insuf ficiently expressed in cell types of this organ in which the pigments are produced. Insertion of the anther box, a homologous sequence found in other genes expressed in anthers, resulted in a modified expressio n pattern driven by this promoter, as monitored by the beta-glucuronid ase (gus) gene. In addition to the basic CaMV 35S expression pattern i n anthers, GUS activity was observed in tapetum cells when the modifie d promoter was fused to the gus gene. This promoter construct was subs equently used to drive an antisense chs gene in transgenic petunia, wh ich led to the inhibition of pigment synthesis in anthers of five of 3 5 transformants. Transgenic plants with white anthers were male steril e due to an arrest in male gametophyte development. This finding indic ated that flavonoids play an essential role in male gametophyte develo pment.