Abstract
The flower of Hedychium coronarium possesses highly specialized floral organs: a synsepalous calyx, petaloid staminodes and a labellum. The formation of these organs is controlled by two gene categories: floral organ identity genes and organ boundary genes, which may function individually or jointly during flower development. Although the floral organogenesis of H. coronarium has been studied at the morphological level, the underlying molecular mechanisms involved in particular organ morphologies that emerge in flower development still remain poorly understood. Here, we used comparative transcriptomics combined with Real-time quantitative PCR to investigate gene expression patterns of ABC-class genes in H. coronarium flowers, as well as the homolog of PETAL LOSS (HcPTL). Our studies found that stamen/petal identity or stamen fertility in H. coronarium was not necessarily correlated with the differential expression of HcAP3 and HcAG. We also found a novel spatio-temporal expression pattern for HcPTL mRNA, suggesting it may have evolved a lineage-specific role in the morphogenesis of the Hedychium flower. Our study provides a new transcriptome reference and a functional hypothesis regarding the role of a boundary gene in organ fusion that should be further addressed through phylogenetic analyzes of this gene, as well as functional studies.
Highlights
The flower of Hedychium coronarium possesses highly specialized floral organs: a synsepalous calyx, petaloid staminodes and a labellum
Here, we used comparative transcriptomics combined with Real-time quantitative PCR and mRNA in situ hybridization to investigate gene expression patterns of ABC-class genes in H. coronarium flowers, as well as the homolog of the organ boundary gene PETAL LOSS (HcPTL). qRT-PCR detection showed that HcAP3 and HcAG were expressed in both the petaloid staminode and the fertile stamen. mRNA in situ hybridization showed that HcPTL was expressed in developing meristems, including cincinnus primordia, floral primordia, common primordia and almost all new initiating floral organ primordia
We found a novel spatio-temporal expression pattern for HcPTL mRNA, suggesting it may have evolved a lineage-specific role in the morphogenesis of the Hedychium flower
Summary
The flower of Hedychium coronarium possesses highly specialized floral organs: a synsepalous calyx, petaloid staminodes and a labellum. The formation of these organs is controlled by two gene categories: floral organ identity genes and organ boundary genes, which may function individually or jointly during flower development. A typical Zingiberaceae flower possesses four concentric whorls of floral organs: the outer perianth whorl (whorl 1) which consists of three sepals; the inner perianth whorl (whorl 2) composed of three petals; a single fertile stamen and five staminodes comprise the androecial whorl (whorl 3), in which 2–4 petaloid staminodes normally fuse to form a distinctive labellum; and the innermost whorl (whorl 4), which bears a tricarpellary pistil. While the floral organogenesis of H. coronarium has been studied in depth at the morphological level [4], the underlying molecular mechanisms involved in its floral organ development are still unknown
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