Floral organ transcriptome in Camellia sasanqua provided insight into stamen petaloid

Abstract

Background: The cultivated Camellia sasanqua forms a divergent double flower pattern, and the stamen petaloid is a vital factor in the phenomenon. However, the regulation mechanism remains largely unclear.

Results: Here, a comprehensive comparative transcriptome analysis of the wild-type, "semi-double", "peony double", and "rose double" was performed. The cluster analysis of global gene expression level showed petal and stamen difficulty separable in double flower. The crucial pathway and genes related to double flower patterns regulation were identified by pairwise comparisons and weighted gene coexpression network (WGCNA). Divergent genes expression, such as AUX1 and AHP, are involved in plant hormone signaling and photosynthesis, and secondary metabolites play an important role. Notably, the diversity of a petal-specific model exhibits a similar molecular signature to the stamen, containing extensin protein and PSBO1, supporting the stamen petaloid point. Moreover, the expansion of class A gene activity influenced the double flower formation, showing that the key function of gene expression was probably demolished.

Conclusions: Overall, this work confirmed the ABCE model and provided new insights for elucidating the molecular signature of double formation.

Keywords: ABCE model; Camellia sasanqua; Double flower; Petaloid stamen; Phytohormone; Transcriptome.

Fig. 1

Phenotype divergence of C. sasanqua wild-type (single flower) and cultivated double flowers. A The diagram illustrates the four whorls of the floral organ in C. sasanqua, including carpel, stamen, petal, and sepal. B Whole flower comparison among single flower, semi-double, rose double, and peony double

Fig. 2

The transcription divergence of the floral organ. A Venn plots of DEGs among homologous organs of different flower patterns, the red mark indicates a specified comparison group. B The highly enriched GO terms and their distributions among comparisons. The number indicate the overlap mark in (A). C The highly enriched KEGG pathway and their distributions among comparisons. The numbers indicate the overlap mark in A

Fig. 3

Weighted gene coexpression network analysis of floral organ. A Correlation between the gene model and the petal, stamen, and sepal of different flower patterns in the coexpression network. The correlation coefficient and the p-value are shown within each cell. The right panel is a color scale for correlating module traits from -1 to 1. B The expression heatmap of all genes in model grey60. Yellow and blue indicate high and low expression levels, respectively. C The correlation network of the grey60 module with the high edge weight as visualized by Cytoscape. D The top 10 enriched GO terms in the grey60 model. E The top 10 enriched KEGG pathways in the grey60 model

Fig. 4

Expression heatmap of the DEGs involved in plant hormone pathways. RNA-seq data were normalized based on the mean expression value of each gene, yellow and blue indicate high and low expression levels, respectively

Fig. 5

Identification and expression analysis of MADS-box genes. A Phylogenetic tree of MADS-box genes in C. sasanqua and Arabidopsis. The colored region indicated the ABCE model genes subgroups. B The expression heatmap of ABCE class genes in C. sasanqua, yellow and blue, indicate high and low expression levels, respectively

Fig. 6

The expression levels of 5 genes at different tissues for RT-qPCR and the RNA-Seq experiment, red and blue indicated RT-qPCR and transcriptome data, respectively