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

Abstract

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.

Breaking the mold: understanding the evolution and development of lateral organs in diverse plant models

“…Stamens are highly modified lateral organs that, in most angiosperms, have lost their laminar expansion, resulting in narrow filaments topped by bulbous microsporangia. Recent work hypothesizes that the lack of laminar expansion results from unbalanced expression of adaxial/abaxial factors [47]. Functional studies are needed to test hypothesis, but this model of altering organ shape by modifying polarity is consistent with what has been seen in highly modified leaves.…”

Comparative analysis of whole flower transcriptomes in the Zingiberales

“…Throughout the evolution of the Zingiberales, the number of fertile stamens is drastically reduced from 5–6 fertile stamens in the banana lineages to one or fertile stamen in the ginger clade. This reduction in fertile stamen number is inversely correlated to an increase in petaloidy, in which the infertile androecial members laminarize (flatten) and develop into petal-like organs ( Almeida, Yockteng & Specht, 2015 ) ( Fig. 1B ).…”

Expression and Function Studies of CYC/TB1-Like Genes in the Asymmetric Flower Canna (Cannaceae, Zingiberales)

“…In flowers of the Zingiberalean ginger families (Costaceae, Zingiberaceae, Cannaceae, and Marantaceae), petaloid staminodes account for the "showy" aspect of the floral display, taking on the role and function typically held by petals. The androeciumderived "petaloid" structures are, however, different from secondwhorl petals in their appearance and epidermal cell morphology (Almeida et al, 2015), indicating that mechanisms making a petaloid structure may not be homologous across the whorls. In this research, the genomic presence and expression of endogenous CYC/TB1-like genes was studied to determine their potential role in generating petaloid structures and thereby effecting overall patterns of floral symmetry.…”