GSE60105
Analysis of transcriptome sequences from two flower types of C. vulgaris
The production of heather (Calluna vulgaris) in Germany is highly dependent on cultivars with mutated flower morphology, the so-called diplocalyx bud bloomers. So far, this unique flower type of C. vulgaris has not been reported in any other plant species. The flowers are characterised by an extremely extended flower attractiveness, since the flower buds remain closed throughout the complete flowering season. The flowers of C. vulgaris bud bloomers are male sterile, because the stamens are missing. Furthermore, petals are converted into sepals. Therefore the diplocalyx bud bloomer flowers consist of two whorls of sepals directly followed by the gynoecium. A broad comparison of wild type and bud bloomer’s flowers was undertaken to identify genes differentially expressed in the bud flowering phenotype and in the wild type of C. vulgaris. Transcriptome sequence reads were generated using next generation 454 sequencing of two flower type specific cDNA libraries. In total, 360,000 sequence reads were obtained, assembled to 12,200 contigs, functionally mapped, and annotated. Transcript abundances in wild type and bud bloomer’s libraries were compared and 365 differentially expressed genes detected. Among these differentially genes, CvPI was identified which is the orthologue of the Arabidopsis B gene PISTILLATA (PI) and considered as the most promising candidate gene. Quantitative PCR was performed to analyse the gene expression levels of two C. vulgaris B genes CvPI and CvAP3 in both flower types. CvAP3 which is the orthologue of the Arabidopsis B gene APETALA (AP3) turned out to be ectopically expressed in sepals of wild type and bud bloomer flowers. CvPI expression was proven to be reduced in the flowers of bud blooming cultivars. Differential expression patterns of the B-class genes CvAP3 and CvPI were identified to cause characteristics of flower morphology in C. vulgaris wild type and bud blooming flowers leading to the following hypotheses: ectopic expression of CvAP3 is a convincing explanation for the formation of a completely petaloid perianth in the wild type and the “bud flowering” phenotype. In C. vulgaris, CvPI is essential for determination of petal and stamen identity. The characteristic transition of petals into sepals potentially depends on the observed deficiency of CvPI and CvAP3 expression in bud blooming flowers. However, the complete loss of stamens in bud blooming flowers remains to be explained. Overall design: two samples were analysed, each representing a flower type