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

Double flowers in cultivated camellias are divergent in floral patterns which present a rich resource for demonstrating molecular modifications influenced by the human demands. Despite the key principle of ABCE model in whorl specification, the underlying mechanism of fine-tuning double flower formation remains largely unclear. Here a comprehensive comparative transcriptomics interrogation of gene expression among floral organs of wild type and "formal double" and "anemone double" is presented. Through a combination of transcriptome, small RNA and "degradome" sequencing, we studied the regulatory gene expression network underlying the double flower formation. We obtained the differentially expressed genes between whorls in wild and cultivated Camellia. We showed that the formation of double flowers tends to demolish gene expression canalization of key functions; the faded whorl specification mechanism was fundamental under the diverse patterns of double flowers. Furthermore, we identified conserved miRNA-targets regulations in the control of double flowers, and we found that miR172-AP2, miR156-SPLs were critical regulatory nodes contributing to the diversity of double flower forms. This work highlights the hierarchical patterning of global gene expression in floral development, and supports the roles of "faded ABC model" mechanism and miRNA-targets regulations underlying the double flower domestication.