Resumen de Molecular Analysis of Flower Bilateral Symmetry
J. A. P. Raimundo, R. Sobral, E. S. Coen, M. M. R. Costa
Bilateral symmetry in flowers has evolved independently multiple times in different speciesfrom radially symmetric ancestors. In Antirrhinum majus, bilateral symmetry of the flowerrequires the combined activity of four key genes: CYCLOIDEA (CYC), DICHOTOMA (DICH),RADIALIS (RAD) and DIVARICATA (DIV). We are currently analysing how these genes, allcoding for transcription factors, interact to establish an asymmetric pre-pattern in theAntirrhinum flower meristem and exploring the extent to which these processes are conserved inArabidopsis, a species with radial symmetric flowers.CYC, DICH and RAD are expressed dorsally in floral primordia and promote dorsal petal andstamen identity. DIV is expressed all round the floral primordium, even though it has only aphenotypic effect in the ventral region of the flower. Genetic and molecular studies haverevealed that RAD is a direct target of CYC and antagonises the activity of DIV. RAD and DIVcode for two related MYB-like genes and they are thought to compete for a common DNAbindingsite or co-factor. The DNA consensus binding sequence for DIV was obtained byrandom binding-site selection and we showed that RAD does not antagonise DIV throughcompetitive binding to DNA, implying that the antagonism may involve interactions with otherproteins. In a yeast 2-hybrid screen, two novel MYB-like proteins (RIPs, RAD-InteractingProteins) were identified that interact with both RAD and DIV. The transcript abundance andlocalization of the RIPs was analysed by RT-PCR and in situ hybridization and the subcelularlocalization of the RIPs, RAD and DIV proteins was determined using transient assays intobacco leaf epidermis.The RIP proteins belong to a new class of MYB-like proteins present in dicots, monocots andbryophytes. In order to understand the role of this gene family during evolution, we arecharacterising the five RIP-like genes of Arabidopsis. We have analysed their expression patternby RT-PCR, analysed insertion mutant plants and generated over-expression lines.
