Abstract
Floral organs that take on the characteristics of petals can occur in all whorls of the monocot order Zingiberales. In Canna indica, the most ornamental or 'petaloid' parts of the flowers are of androecial origin and are considered staminodes. However, the precise nature of these petaloid organs is yet to be determined. In order to gain a better understanding of the genetic basis of androecial identity, a molecular investigation of B- and C-class genes was carried out. Two MADS-box genes GLOBOSA (GLO) and AGAMOUS (AG) were isolated from young inflorescences of C. indica by 3' rapid amplification of cDNA ends polymerase chain reaction (3'-RACE PCR). Sequence characterization and phylogenetic analyses show that CiGLO and CiAG belong to the B- and C-class MADS-box gene family, respectively. CiAG is expressed in petaloid staminodes, the labellum, the fertile stamen and carpels. CiGLO is expressed in petals, petaloid staminodes, the labellum, the fertile stamen and carpels. Expression patterns in mature tissues of CiGLO and CiAG suggest that petaloid staminodes and the labellum are of androecial identity, in agreement with their position within the flower and with described Arabidopsis thaliana expression patterns. Although B- and C-class genes are important components of androecial determination, their expression patterns are not sufficient to explain the distinct morphology observed in staminodes and the fertile stamen in C. indica.
Highlights
A landmark accomplishment in plant developmental biology was the proposition of the ABC model of flower organ identity
The CiAG sequence is similar to the AG-like family in comparison to other MADS-box genes in GenBank including A. oblongifolia (ABB92624), A. hainanensis (AAT99428), A. thaliana (NP_567569), O. sativa (ACY26070) and N. tabacum (Q43585), and it is most similar to AoAG (DQ286724) from A. oblongifolia (Gao et al 2006) and AhMADS6 (AY621155) from A. hainanensis (Song et al 2010) (Fig. 2A)
CiGLO is similar in sequence to the GLOBOSA subfamily in comparison to other MADS-box genes from GenBank including Canna sp. (GU594945), A. oblongifolia (ABB92623), A. hainanensis (AAT99429), A. thaliana (NP_197524), O. sativa (NP_001045012) and N. tabacum (Q03416)
Summary
A landmark accomplishment in plant developmental biology was the proposition of the ABC model of flower organ identity. This model provides a framework for describing a conserved pattern of gene expressions associated with the specification of floral organs in model species (Bowman et al 1991; Coen and Meyerowitz 1991). Studies in other angiosperm lineages generally support the idea that the expression patterns described by the ABC model are widely conserved, at least among eudicots. The extent to which the eudicot-based ABC model of flower organ identity describes floral morphologies in monocots is still not well understood (Ambrose et al 2000)
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