Genomic level views of novel floral organ morphology

Abstract

Across the angiosperms there are many examples of independently derived, novel floral organs. The presence of such structures results in five or more distinct floral organ identities, which is difficult to reconcile with the canonical ABC model. In the emerging model system Aquilegia there are five differentiated floral organ types: petaloid sepals, spurred petals, stamens, staminodia and carpels. This morphology would seem to require modifications of the ABC model, namely the capacity to specify two types of petaloid organs as well as a fifth organ identity. Detailed expression studies of the three APETALA3 (AP3) paralogs and one PISTILLATA (PI) homolog in Aquilegia demonstrate that each organ type expresses a specific combination of genes. Furthermore, RNAi-mediated knock-down of B homolog function has found that these loci are essential to staminodium, stamen and petal identity, but play only subtle developmental roles in the petaloid sepals. Our findings show that pre-existing floral organ identity programs can be partitioned and modified to produce additional organ types. As an extension of this work, we are using RNAi to knock down the function of each AP3 paralog independently, which has revealed evidence for both suband neofunctionalization. To complement our candidate gene approach, we are using Illumina-based sequencing of homeotic mutants as well as laser microdissected samples to gain greater insight into the genetic basis of identity and developmental elaboration in the novel floral organs of Aquilegia.