Gerbera

Abstract: The ornamental plant Gerbera hybrida bears complex inflorescences with morphologically distinct floral morphs that are specific to the sunflower family Asteraceae. We have previously characterized several MADS box genes that regulate floral development in Gerbera. To study further their behavior in higher order complex formation according to the quartet model, we performed yeast two- and three-hybrid analysis with fourteen Gerbera MADS domain proteins to analyze their protein-protein interaction potential. The exhaustive pairwise interaction analysis showed significant differences in the interaction capacity of different Gerbera MADS domain proteins compared to other model plants. Of particular interest in these assays was the behavior of SEP-like proteins, known as GRCDs in Gerbera. The previously described GRCD1 and GRCD2 proteins, which are specific regulators involved in stamen and carpel development, respectively, showed very limited pairwise interactions, whereas the related GRCD4 and GRCD5 factors displayed hub-like positions in the interaction map. We propose GRCD4 and GRCD5 to provide a redundant and general E function in Gerbera, comparable to the SEP proteins in Arabidopsis. Based on the pairwise interaction data, combinations of MADS domain proteins were further subjected to yeast three-hybrid assays. Gerbera B function proteins showed active behavior in ternary complexes. All Gerbera SEP-like proteins with the exception of GRCD1 were excellent partners for B function proteins, further implicating the unique role of GRCD1 as a whorl- and flower-type specific C function partner. Gerbera MADS domain proteins exhibit both conserved and derived behavior in higher order protein complex formation. This protein-protein interaction data can be used to classify and compare Gerbera MADS domain proteins to those of Arabidopsis and Petunia. Combined with our reverse genetic studies of Gerbera, these results reinforce the roles of different genes in the floral development of Gerbera. Building up the elaborate capitulum of Gerbera calls for modifications and added complexity in MADS domain protein behavior compared to the more simple flowers of, e.g., Arabidopsis.

Abstract: • Chalcone synthase (CHS) is the key enzyme in the first committed step of the flavonoid biosynthetic pathway and catalyzes the stepwise condensation of 4-coumaroyl-CoA and malonyl-CoA to naringenin chalcone In plants, CHS is often encoded by a small family of genes that are temporally and spatially regulated Our earlier studies have shown that GCHS4 is highly activated by ectopic expression of an MYB-type regulator GMYB10 in gerbera (Gerbera hybrida) • The tissue- and development-specific expression patterns of three gerbera CHS genes were examined Virus-induced gene silencing (VIGS) was used to knock down GCHS1 and GCHS4 separately in gerbera inflorescences • Our data show that GCHS4 is the only CHS encoding gene that is expressed in the cyanidin-pigmented vegetative tissues of gerbera cv Terraregina GCHS3 expression is pronounced in the pappus bristles of the flowers Expression of both GCHS1 and GCHS4 is high in the epidermal cells of gerbera petals, but only GCHS1 is contributing to flavonoid biosynthesis • Gerbera contains a family of three CHS encoding genes showing different spatial and temporal regulation GCHS4 expression in gerbera petals is regulated post-transcriptionally, at the level of either translation elongation or protein stability

Abstract: We have developed a regeneration method and an Agrobacterium-mediated transformation protocol for the commercially important ornamental plant Gerbera hybrida. Pieces of petioles of the red variety Terra Regina were cocultivated with a disarmed Agrobacterium tumefaciens vector containing a nearly full-length antisense cDNA encoding gerbera chalcone synthase under the control of CaMV 35S promoter, and a nos-nptII marker gene. The transformed cells were selected on the basis of kanamycin resistance and regenerated into flowering plants. Introduction of the antisense cDNA blocked anthocyanin synthesis and resulted in a dramatically altered flower pigmentation in some of the transformants.