Distinct double flower varieties in Camellia japonica exhibit both expansion and contraction of C-class gene expression

Abstract

BackgroundDouble flower domestication is of great value in ornamental plants and presents an excellent system to study the mechanism of morphological alterations by human selection. The classic ABC model provides a genetic framework underlying the control of floral organ identity and organogenesis from which key regulators have been identified and evaluated in many plant species. Recent molecular studies have underscored the importance of C-class homeotic genes, whose functional attenuation contributed to the floral diversity in various species. Cultivated Camellia japonica L. possesses several types of double flowers, however the molecular mechanism underlying their floral morphological diversification remains unclear.ResultsIn this study, we cloned the C-class orthologous gene CjAG in C. japonica. We analyzed the expression patterns of CjAG in wild C. japonica, and performed ectopic expression in Arabidopsis. These results revealed that CjAG shared conserved C-class function that controls stamen and carpel development. Further we analyzed the expression pattern of CjAG in two different C. japonica double-flower varieties, ‘Shibaxueshi’ and ‘Jinpanlizhi’, and showed that expression of CjAG was highly contracted in ‘Shibaxueshi’ but expanded in inner petals of ‘Jinpanlizhi’. Moreover, detailed expression analyses of B- and C-class genes have uncovered differential patterns of B-class genes in the inner organs of ‘Jinpanlizhi’.ConclusionsThese results demonstrated that the contraction and expansion of CjAG expression were associated with the formation of different types of double flowers. Our studies have manifested two different trajectories of double flower domestication regarding the C-class gene expression in C. japonica.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0288-1) contains supplementary material, which is available to authorized users.

Global gene expression defines faded whorl specification of double flower domestication in Camellia

“…Previous studies in Camellia characterized the expression of A-, and C- function genes and suggested that double flower domestication were involved in multiple pathways 27 . Interestingly, the expression of C function ortholog ( CjAG ) displayed opposite patterns in petals of formal and anemone doubles (expression of CjAG suppressed in formal double, but upregulated in anemone double) 27 . Despite the extensive knowledge on genetic regulation of floral development in the model plant species, it remains unclear how the floral patterns in cultivated Camellia were achieved.

Figure 1Comparative transcriptomics analysis in wild and doubled camellias.

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Ranunculacean flower terata: Records, a classification, and some clues about floral developmental genetics and evolution

“…For example, in filled flowers, stamens and carpels are replaced by sepals and petals; according to the ABC model, C-class gene expression is expected to be affected in the innermost whorls. Such a hypothesis has been confirmed in filled flowers of Camellia japonica (Sun et al, 2014) and Ipomoea nil (Nitasaka, 2003). Similarly, double flowers with an increased number of petals and/or petaloid stamens and a decrease in stamen number, may correspond to mutation(s) shifting the expression domain of C-class genes.…”

“…Similarly, double flowers with an increased number of petals and/or petaloid stamens and a decrease in stamen number, may correspond to mutation(s) shifting the expression domain of C-class genes. Such a shift in the expression domain of AG homologues has been described in species with double flowers belonging to Rosa sp, Prunus lannesiana, Camellia japonica and Lilium (Dubois et al, 2010;Liu et al, 2013;Sun et al, 2014;Akita et al, 2008Akita et al, , 2011. In the Orchidaceae family, the characterization of genes from the extended ABCE model, with a focus on the B-class genes has given clues about the genetic origin of peloric flowers in some species.…”

Floral Morphology and MADS Gene Expression in Double-flowered Japanese Evergreen Azalea

“…Thus, attenuated Cclass function could increase petal development, inhibit stamen development, and also increase the floral organ number, which is consistent with the formation of double flowers. Double-flowered phenotypes result from C-function repression in a number of horticultural plants, including Gentiana scabra (Nakatsuka et al, 2015), Camellia japonica (Sun et al, 2014), Petunia hybrida (Noor et al, 2014), and Cyclamen persicum (Tanaka et al, 2013). Therefore, it is likely that the double flowers of Japanese azalea cultivars result from lost or impaired C-function genes.…”

“…In addition to transgenic flowers, the double-flowered cultivar 'Shibaxueshi' (Camellia japonica) is a typical formal double type with petals from the outer layer to the inside. Furthermore, the stamens and carpels were missing and the expression levels of CjAG in floral buds were markedly reduced, suggesting that the loss of CjAG expression is involved in double flower development (Sun et al, 2014). In Cyclamen double-flowered cultivars, the lack of CpAG1 expression causes the homeotic conversion of stamens and carpels into petals (Tanaka et al, 2013).…”