A BHLH TRANSCRIPTION FACTOR MEDIATES ORGAN, REGION AND FLOWER TYPE-SPECIFIC SIGNALS ON DIHYDROFLAVONOL-4-REDUCTASE (DFR) GENE-EXPRESSION INTHE INFLORESCENCE OF GERBERA-HYBRIDA (ASTERACEAE)

The angiosperm family Asteraceae is characterized by composite inflore scences, which are highly organized structures consisting of different types of flowers. In order to approach the control of floral organ di fferentiation in Asteraceae at molecular level, we are studying regula tion of flavonoid biosynthesis in Gerbera hybrida. Dihydroflavonol-4-r eductase (dfr) expression is regulated according to anthocyanin pigmen tation patterns in ail tested gerbera varieties at several anatomical levels. We have isolated a promoter for one of the dfr genes, Pgdfr2. Gerbera plants transgenic for a Pgdfr2-uidA construct reveal that the activity of the Pgdfr2 promoter from one variety follows the pigmentat ion in other varieties which have different color patterns. It is thus evident that the observed complex regulation of dir expression occurs in trans. In order to identify the trans-acting regulators, we isolat ed a cDNA (gmyc1) homologous to the previously characterized genes enc oding bHLH-type regulators of the anthocyanin pathway in plants. the e xpression of gmyc1 in different varieties suggests that it has a major role in regulating dfr activity in corolla and carpel, but not in pap pus and stamen. Specifically in gerbera, the identical patterns of gmy c1 and dir expression in corolla tissue suggest that GMYC1 also regula tes dir expression in a region and flower type specific manner. Our st udies show that in gerbera GMYC1-dfr interaction is part of several de velopmental processes characteristic far Asteraceae (such as specifica tion of flower types across the composite inflorescence), whereas in o ther processes (such as differentiation of sepal as pappus) other regu lators control dfr expression to determine the spatial specificity.