Instead of forming an elongated inflorescence bearing ebracteate flowers like most members of the family, Idahoa, Leavenworthia, and Ionopsidium produce flowers in the axils of bract-leaves and do so without noticeable internode elongation. A phylogenetic analysis shows that these three genera independently evolved these phenotypes. In the long run we hope to determine the developmental and genetic basis for these evolution events.

Based on work in Arabidopsis the genes LEAFY and APETALA1 seem to be good candidates for involvement in at least some aspects of the phenotype. To date we have focused on LFY. A former post-doc Guoping Shu  (Shu et al. 2000) looked at the comparative expression of this gene in Ionopsidium acaule using in situ hybridization, finding an unusual expression pattern involving expression in vegetative shoot apical meristems (SAM).

We have cloned and sequenced LFY genes from a number of different species. Ho-Sung Yoon cloned LFY and 3' and 5' sequences from the three rosette-flowering lineages and introduced these into Arabidopsis plants that are homozygous mutant at the endogenous LFY locus. He found (Yoon and Baum, 2004) that the Ionopsidium acaule transgene (IacLFY) had no effect on plant architecture.  The Leavenworthia crassa gene (LcrLFY) causes the production of terminal flowers. One of the two Idahoa scapigera genes (IscLFY1: we are now conducting the equivalent experiment for IscLFY2) caused the production of flowers resembling ap1 mutants and of some shoots with compressed internodes and extra floral bracts.  Ho-Sung also examined the expression driven by the 5' non-coding sequences of the three transgenes in Arabidopsis. The IacLFY enhancer/promoter drove expression just like the control AthLFY, the LcrLFY promoter drove expression in the SAM (explaining terminal flower production), whereas the IscLFY1 promoter drove expression that resembled AthLFY except for a lack of expression in petals and sepals (explain the ap1 phenotype).

Post-doc Marek Sliwinski and research specialist Yolibeth Rangel are conducting additional transgenic experiments to look at those regions of the four LFY loci responsible for the transgenic phenotypes and altered expression of reporter genes.  Future work will involve: (1) analogous experiments for other candidate genes (e.g., AP1, TFL1, JAG); (2) more detailed studies of architectural variation within Ionopsidium; (3) exploratory use of a transgenomic strategy to identify genes responsible for phenotypic differences between different species of Brassicaceae.