Perspectives on MADS-box expression during orchid flower evolution and development.

Mariana Mondragón-Palomino

doi:10.3389/fpls.2013.00377

Abstract

The diverse morphology of orchid flowers and their complex, often deceptive strategies to become pollinated have fascinated researchers for a long time. However, it was not until the 20th century that the ontogeny of orchid flowers, the genetic basis of their morphology and the complex phylogeny of Orchidaceae were investigated. In parallel, the improvement of techniques for in vitro seed germination and tissue culture, together with studies on biochemistry, physiology, and cytology supported the progress of what is now a highly productive industry of orchid breeding and propagation. In the present century both basic research in orchid flower evo-devo and the interest for generating novel horticultural varieties have driven the characterization of many members of the MADS-box family encoding key regulators of flower development. This perspective summarizes the picture emerging from these studies and discusses the advantages and limitations of the comparative strategy employed so far. I address the growing role of natural and horticultural mutants in these studies and the emergence of several model species in orchid evo-devo and genomics. In this context, I make a plea for an increasingly integrative approach.

Highlights

The diverse morphology of orchid flowers and their complex, often deceptive strategies to become pollinated have fascinated researchers for a long time
In the present century both basic research in orchid flower evo-devo and the interest for generating novel horticultural varieties have driven the characterization of many members of the MADS-box family encoding key regulators of flower development
It was hard to explain the differences on their patterns of expression: while FBP2 was expressed in petals, stamens, carpels and at a very low level in sepals (Angenent et al, 1992), om1 was detected in the first and second perianth whorls of x Aranda “Deborah.” It was after 2000, when many more MADS-box genes from model species had been characterized and the phylogeny of this family was extensively investigated, that om1 was confirmed as a SEPALLATA3-like gene (Zahn et al, 2005) and expression of om1 orthologs DOMADS1 and DcOSEP1 from Dendrobium was confirmed in the perianth as well as in the gynostemium and ovary (Figures 1A,B) (Yu and Goh, 2000; Xu et al, 2006)

Summary

Introduction

The diverse morphology of orchid flowers and their complex, often deceptive strategies to become pollinated have fascinated researchers for a long time. The dimeric and multimeric interactions of orchid MADS domain proteins have been described in Oncidium “Gower Ramsey,” Dendrobium crumenatum, Phalaenopsis equestris and Cymbidium ensifolium (Hsu and Yang, 2002; Xu et al, 2006; Tsai et al, 2008; Chang et al, 2010; Wang et al, 2011; Chen et al, 2012) (Table 1, underlined gene names).

Results

Conclusion