Evolution of petaloidy in the zingiberales: An assessment of the relationship between ultrastructure and gene expression patterns

Background: The development of petal-like organs has occurred repetitively throughout angiosperm evolution. Despite homoplasy, it is possible that common underlying molecular mechanisms are repeatedly recruited to drive the development of petaloid organs. In Zingiberales, infertile, petal-like structures replace fertile stamens, resulting in petaloidy in androecial whorls. Assuming that androecial petaloidy is a shared derived characteristic, we expect to find common ultrastructure and molecular mechanisms underlying androecial petaloidy across Zingiberales. Results: We show that petaloidy in Zingiberales is associated with tightly packed, protruding epidermal cells. Expression patterns for candidate genes involved in petal identity differ between the petaloid organs of Costaceae v. Cannaceae, despite similar macro- and microscopic organization. For all candidate gene families analyzed, our data suggest at least one Zingiberales-specific duplication event. Conclusions: Our data suggest that the patterns of B-class gene expression across the Zingiberales do not correlate with the occurrence of petaloidy, indicating that androecial petaloidy might have evolved independently of B-class gene expression in some lineages. It is possible that gene duplication may play a role in the diversity of petaloid structures found throughout the Zingiberales. It is likely that Zingiberales petaloidy may also result from the deployment of genes other than those involved in specification of petal identity. Developmental Dynamics 244:1121–1132, 2015. © 2015 Wiley Periodicals, Inc.