GRCD1, an AGL2-like MADS box gene, participates in the C function during stamen development in Gerbera hybrida

Despite the differences in flower form, the underlying mechanism in determi ning the identity of floral organs is largely conserved among different ang iosperms, but the details of how the functions of A, B, and C are specified varies greatly among plant species. Here, we report functional analysis of a Gerbera MADS box gene, GRCD1, which is orthologous to AGL2-like MADS box genes. Members of this group of genes are being reported in Various specie s in growing numbers, but their functions remained largely unsettled, GRCD1 expression is detected in all four whorls, but the strongest signal is see n in the developing stamen and carpel. Downregulating GRCD1 expression by a ntisense transformation revealed that lack of GRCD1 caused homeotic changes in one whorl only: sterile staminodes, which normally develop in whorl 3 o f marginal female florets, were changed into petals. This indicates that th e GRCD1 gene product is active in determining stamen identity. Transgenic d ownregulation of GRCD1 causes a homeotic change similar to that in the down regulation of the Gerbera C function genes GAGA1 and GAGA2, but one that is limited to whorl 3, Downregulation of GRCD1 expression does not reduce exp ression of GAGA1 or GAGA2, or vice versa; and in yeast two-hybrid analysis, GRCD1 is able to interact with GAGA1 and GAGA2. We propose that a heterodi mer between the GRCD1 and GAGA1/2 gene products is needed to fulfill the C function in whorl 3 in Gerbera.