Male and female flowers of the dioecious plant sorrel show different patterns of MADS box gene expression.

Abstract

Male and female flowers of the dioecious plant sorrel (Rumex acetosa) each produce three whorls of developed floral organs: two similar whorls of three perianth segments and either six stamens (in the male) or a gynoecium consisting of a fertile carpel and two sterile carpels (in the female). In the developing male flower, there is no significant proliferation of cells in the center of the flower, in the position normally occupied by the carpels of a hermaphrodite plant. In the female flower, small stamen primordia are formed. To determine whether the organ differences are associated with differences in the expression of organ identity genes, cDNA clones representing the putative homologs of B and C function MADS box genes were isolated and used in an in situ hybridization analysis. The expression of R A D l and RADP (two different DEFlClENS homologs) in males and females was confined to the stamen whorl; the lack of expression in the second, inner perianth whorl correlated with the sepaloid nature of the inner whorl of perianth segments. Expression of R A P l (a PLENA homolog) occurred in the carpel and stamen whorls in very young flower primordia from both males and females. However, as soon as the inappropriate set of organs ceased to develop, R A P l expression became undetectable in those organs. The absence of expression of R A P l may be the cause of the arrest in organ development or may be a consequence.

Origin and evolution of petals in angiosperms

“…In the hexamerous flower the sepals are arranged in two whorls of three and often become differentiated morphologically, especially at fruiting, closely resembling a trimerous flower (Ronse De Craene 2010). Ainsworth et al (1995) found no B-gene expression in the perianth of Rumex, but confuse petals with sepals in suggesting that sepaloidy is the result of a secondary restriction of petaloidy in the 'petals'. However, the flower in Polygonaceae is basically apetalous.…”

“…Albert et al 1998, Kramer et al 1998, Lamb & Irish 2003, Ronse De Craene 2007, Rasmussen et al 2009, Irish 2009). These studies have focussed on the canonical ABC(DE) model to explain the molecular control of floral organ identities.…”

“…In general, homologues of eudicot AP3 and PI are found in monocots (Gao et al 2006) and shifting boundaries in the expression of these B-class MADS-box genes have been hypothesised to explain the transition between a differentiated perianth and an undifferentiated perianth comprised of petaloid tepals (Albert et al 1998, Kramer et al 2003). This has been illustrated for Liliales (e.g.…”

“…The result of this compression is a potential to increase the number of perianth parts and to ultimately develop a biseriate perianth (cf. Venkata Rao 1963, Drinnan et al 1994, Albert et al 1998, Ronse De Craene 2007 3F) and bracts may occasionally fuse with sepals (e.g. Macro carpaea: Albert et al 1998).…”

“…In addition two other gene classes have later been identified: D-class genes control ovule development and Eclass genes act as mediators in the development of all floral organ identities (see Pelaz et al 2000, Theissen 2001, Becker & Theissen 2003. With reference to petal development, the B-class MADS-box genes PISTILLATA (PI) and APETA-LA3 (AP3) or GLOBOSA (GLO) and DEFICIENS (DEF) in Arabidopsis and Antirrhinum respectively have been shown to be of particular importance: (1) B-class MADS-box genes are generally expressed in the second whorl petals of a differentiated perianth in core eudicots (see Albert et al 1998, Kim et al 2004, 2005a, Ronse De Craene 2007. (2) In the absence of the C-class MADS-box gene AGAMOUS (AG) or its orthologs, activity of B-class MADS-box genes is necessary for development of the petal in the second whorl of the flower (Jack et al 1992, Mizukami & Ma 1992, Bradley et al 1993, Goto & Meyerowitz 1994.…”