The classical ABC model of floral development was proposed in 1991 to describe the genetic specification of floral organ identity, using data from the eudicots Arabidopsis thaliana and Antirrhinum majus (Bowman et al., 1991; Coen and Meyerowitz, 1991). Since then, studies across angiosperms have revealed that this model can be modified to reflect the gene networks underlying specification of floral organ identity in different angiosperm lineages.

 

The conservation of this model was investigated in the mycoheterotrophic monocot Lacandonia schismatica. This species is endemic to the Lacandon rainforest in Mexico. It is exceptional among angiosperms in that it has “inside-out” flowers: instead of having a central whorl of carpels surrounded by stamens, this taxon is characterized by 2-4 stamens surrounded by many carpels. Expression analyses revealed that B-class and C-class genes, which in Arabidopsis are expressed together in the third whorl to confer stamens, are expressed in the centermost whorl in Lacandonia, consistent with the presence of stamens. Furthermore, the proteins encoded by these genes have conserved interactions with each other and demonstrate functional conservation when expressed in Arabidopsis homeotic mutants. These data suggest that these genes have conserved functions in specifying stamen identity in Lacandonia and support the hypothesis that spatial shift in B-function is what makes these flowers “inside-out.”

--Kelsie Morioka

References

Alvarez-Buylla, E., et al. 2010. B-Function Expression in the Flower Center Underlies the Homeotic Phenotype of Lacandonia schismatica (Triuridaceae). Plant Cell 22:3543-3559.

 

Bowman, J.L., Smyth, D.R., Meyerowitz, E.M. 1991. Genetic interactions among floral homeotic genes of Arabidopsis. Development 112:1-20.

 

Coen, E.S. and Meyerowitz, E.M. 1991. The war of the whorls: genetic interactions controlling flower development. Nature 353:31-37.

 

(photo from) Vergara-Silva, F., et al. 2003. Inside-out flowers characteristic of Lacandonia schismatica evolved at least before its divergence from a closely related taxon, Triuris brevistylis. International Journal of Plant Sciences 164:345-357.