<b>A bHLH transcription factor mediates organ, region and flower type specific signals on dihydroflavonol‐4‐reductase (</b><i><b>dfr</b></i><b>) gene expression in the inflorescence of</b><i><b>Gerbera hybrida</b></i><b>(Asteraceae)</b>

<jats:title>Summary</jats:title><jats:p> <jats:bold>The angiosperm family Asteraceae is characterized by composite inflorescences, which are highly organized structures consisting of different types of flowers. In order to approach the control of floral organ differentiation in Asteraceae at molecular level, we are studying regulation of flavonoid biosynthesis in</jats:bold> <jats:italic> <jats:bold>Gerbera hybrida</jats:bold> </jats:italic> <jats:bold>. Dihydroflavonol‐4‐reductase (</jats:bold> <jats:italic> <jats:bold>dfr</jats:bold> </jats:italic> <jats:bold>) expression is regulated according to anthocyanin pigmentation patterns in all tested gerbera varieties at several anatomical levels. We have isolated a promoter for one of the</jats:bold> <jats:italic> <jats:bold>dfr</jats:bold> </jats:italic> <jats:bold>genes,</jats:bold> <jats:italic> <jats:bold>Pgdfr2</jats:bold> </jats:italic> <jats:bold>. Gerbera plants transgenic for a</jats:bold> <jats:italic> <jats:bold>Pgdfr2</jats:bold> </jats:italic> <jats:bold>‐</jats:bold> <jats:italic> <jats:bold>uidA</jats:bold> </jats:italic> <jats:bold>construct reveal that the activity of the</jats:bold> <jats:italic> <jats:bold>Pgdfr2</jats:bold> </jats:italic> <jats:bold>promoter from one variety follows the pigmentation in other varieties which have different color patterns. It is thus evident that the observed complex regulation of</jats:bold> <jats:italic> <jats:bold>dfr</jats:bold> </jats:italic> <jats:bold>expression occurs</jats:bold> <jats:italic> <jats:bold>in trans</jats:bold> </jats:italic> <jats:bold>. In order to identify the</jats:bold> <jats:italic> <jats:bold>trans</jats:bold> </jats:italic> <jats:bold>‐acting regulators, we isolated a cDNA (</jats:bold> <jats:italic> <jats:bold>gmyc1</jats:bold> </jats:italic> <jats:bold>) homologous to the previously characterized genes encoding bHLH‐type regulators of the anthocyanin pathway in plants. The expression of</jats:bold> <jats:italic> <jats:bold>gmyc1</jats:bold> </jats:italic> <jats:bold>in different varieties suggests that it has a major role in regulating</jats:bold> <jats:italic> <jats:bold>dfr</jats:bold> </jats:italic> <jats:bold>activity in corolla and carpel, but not in pappus and stamen. Specifically in gerbera, the identical patterns of</jats:bold> <jats:italic> <jats:bold>gmyc1</jats:bold> </jats:italic> <jats:bold>and</jats:bold> <jats:italic> <jats:bold>dfr</jats:bold> </jats:italic> <jats:bold>expression in corolla tissue suggest that GMYC1 also regulates</jats:bold> <jats:italic> <jats:bold>dfr</jats:bold> </jats:italic> <jats:bold>expression in a region and flower type specific manner. Our studies show that in gerbera GMYC1–</jats:bold> <jats:italic> <jats:bold>dfr</jats:bold> </jats:italic> <jats:bold>interaction is part of several developmental processes characteristic for Asteraceae (such as specification of flower types across the composite inflorescence), whereas in other processes (such as differentiation of sepal as pappus) other regulators control</jats:bold> <jats:italic> <jats:bold>dfr</jats:bold> </jats:italic> <jats:bold>expression to determine the spatial specificity.</jats:bold> </jats:p>