The double-corolla phenotype in the Hawaiian lobelioid genus Clermontia involves ectopic expression of PISTILLATA B-function MADS box gene homologsReportar como inadecuado

The double-corolla phenotype in the Hawaiian lobelioid genus Clermontia involves ectopic expression of PISTILLATA B-function MADS box gene homologs - Descarga este documento en PDF. Documentación en PDF para descargar gratis. Disponible también para leer online.


, 3:26

First Online: 01 November 2012Received: 30 May 2012Accepted: 05 September 2012


BackgroundThe Hawaiian endemic genus Clermonti a Campanulaceae includes 22 species, 15 of which, the double-corolla species, are characterized by an extra whorl of organs that appear to be true petals occupying what is normally the sepal whorl. Previous research has shown that the presence of homeotic petaloid organs in some other plant groups correlates with ectopic expression of B-function MADS box genes, but similar core eudicot examples of apparent groundplan divergence remain unstudied. B-function genes, which are not normally expressed in the sepal whorl, are required for determination and maintenance of petal identity. Here, we investigate the potential role of altered B-function gene expression contributing to the morphological diversity of this island genus.

ResultsWe examined the morphology and developmental genetics of two different species of Clermontia, one of which, C. arborescens, has normal sepals while the other, C. parviflora, has two whorls of petal-like organs. Scanning electron microscopy of cell surface morphologies of first and second whorl organs in the double-corolla species C. parviflora revealed conical epidermal cells on the adaxial surfaces of both first and second whorl petaloid organs, strongly suggesting a homeotic conversion in the former. Phylogenetic analysis of Clermontia species based on 5S ribosomal DNA non-transcribed spacer sequences indicated a probable single and geologically recent origin of the double-corolla trait within the genus, with numerous potential reversals to the standard sepal-petal format. Quantitative polymerase chain reaction analysis of homologs of the B-function genes PISTILLATA PI, APETALA3 and TOMATO MADS 6 indicated ectopic expression of two PI paralogs in the first whorl of C. parviflora; no such homeotic expression was observed for the other two genes, nor for several other MADS box genes involved in various floral and non-floral functions. In the standard sepal-petal species C. arborescens, ectopic expression of PI homologs was not observed. In C. parviflora, the upregulation of PI homologs was precisely restricted to the perianth and stamen whorls, excluding a simple overexpression phenotype. In situ hybridization analysis of C. parviflora material similarly showed first and second whorl PI homolog expression in developing flower buds.

ConclusionsOur morphological and gene expression data strongly suggest that a drastic and heritable phenotypic change, at the level of floral groundplan, can originate from a homeotic mutation that is likely regulatory, being under precise spatiotemporal control as opposed to having pleiotropic characteristics. The uniqueness of this trait among core eudicots could be linked to increased ecological viability in an unstable island environment, a chance event which need not have posed any immediate adaptive benefit. We argue that the evolutionarily young morphological radiation of Clermontia may form a model system for general understanding of mechanisms of larger-scale angiosperm diversification in past, similarly unstable environments, in which small regulatory changes may have been responsible for modern-day groundplan differences.

KeywordsMyofascial pain Trigger points Neck-shoulder pain Health status AbbreviationsBpbase pairs

qPCRquantitative PCR

RT-PCRreverse-transcriptase polymerase chain reaction

5S-NTS5S ribosomal DNA non-transcribed spacer.

Electronic supplementary materialThe online version of this article doi:10.1186-2041-9139-3-26 contains supplementary material, which is available to authorized users.

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Autor: Katherine A Hofer - Raili Ruonala - Victor A Albert


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