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

Yingkun Sun,Xinlei Li,Jiyuan Li,Hengfu Yin,Zhengqi Fan,Zhongchi Liu

doi:10.1186/s12870-014-0288-1

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.

Highlights

Double 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 deduced protein sequence of CjAG was used to search for closest homologs against different plant species, and according to the result, CjAG was shown to be a member of AG family of MADS-box genes
We found that CjAG was highly conserved among all selected AG family orthologs by sequence alignment analysis (Figure 1A), and two AG motifs located at the Cterminal regions were identified (Figure 1A) which supported that CjAG was an ortholog of AG in C. japonica

Summary

Introduction

Double 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 following studies have elaborated this model to ABC(DE) in which D function controls ovule development and E function (SEP, SEPALLATA family genes) encodes co-factors of A, B, and C floral organ identity genes [10,11,12]. It is much clear in recent years that ‘A function’ might be only specific to Brassicaceae family, and the remaining features of the model seem widely conserved among flowering plants [12,13,14]

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Discussion

Conclusion