Articles
MOLECULAR ANALYSIS OF FLORAL ORGAN DIFFERENTIATION IN GERBERA HYBRIDA
As an article of trade, it ranked sixth in sales through the Dutch auctions in 1991. In Asteraceae, typical specialized features are found both at the level of inflorescence development and of floral organ differentiation.
The former is indicated by the presence of different flower types, and the latter by the special anatomy of sepal (calyx), corolla and the fused anthers.
In order to investigate these differentiation processes at a molecular level, we have taken two opposite approaches.
We have identified a gene that senses the distribution of regulatory molecules inherent for the anatomy of the composite inflorescence.
In Gerbera hybrida, this distribution is displayed in the various patterns of anthocyanin pigmentation of different varieties.
We analyzed gene expression affecting two enzymatic steps, chalcone synthase (CHS) and dihydroflavonol-4-reductase (DFR), of the anthocyanin pathway in five gerbera varieties.
The dfr expression profiles reflect anthocyanin pigmentation at levels of organ identity, flower type and regionally within an organ, while the chs expression varies only occasionally.
In the future we are focusing on the molecular control of dfr expression.
The gerbera dfr is a representative of a hierarchically terminal gene that codes for an enzyme of the secondary metabolism.
The differentiation itself of floral organs is initiated by a combinatorial action of a set of regulatory genes that operate at a high hierarchial level, in the shoot apical meristem reprogrammed to a reproductive phase.
As is the basic structure of the flower, these homeotic, or MADS-box, genes are conserved among flowering plants both in their structure and function.
As a result of differential cDNA library screening between regions of the corolla, we have been able to identify a regulatory gene belonging to the MADS-box family (most closely related to fbp2 of petunia) that operates both during floral organ determination and differentiation.
We believe that by investigating both the regulation of genes that are controlled at different anatomical levels, and the regulatory genes acting from organ determination downstream, we may gradually establish in a complex inflorescence the cascade of gene action from the homeotic genes down to genes that code for enzymes.