Comparative analysis of tree peony petal development by transcriptome sequencing

The tree peony (Paeonia suffruticosa) is an important ornamental flowering plant in China, with the shape of its flowers affecting its ornamental, and therefore, commercial value. Few studies have, however, looked at the molecular factors regulating flower organ development in tree peony. To identify flower shape-related candidate genes, we used transcriptome sequencing to comparatively analyze tree peony during petal development. A total of 16.77 Gb of clean data were assembled and 59,616 unigenes were identified with an N50 value of 1291 bp and a mean size of 888 bp. Fifty-seven percent of the all unigenes identified (33,919 unigenes) were annotated in six databases, where 22,154 unigenes were categorized into 64 gene ontology functional terms, 10,584 unigenes were assigned to 25 clusters of orthologous classifications, and 13,245 unigenes were classified into 127 reference pathways. After differential expression analysis of the unigenes, a total of 4224 differentially expressed genes were identified, of which 1886 unigenes were up-regulated and 2338 down-regulated between the two samples (petals in bud stage and petals in full blooming stage). Seventy-one candidate genes related to petal development were detected and classified into four groups. We believe that a complicated network exists during petal development and that these genes may be involved in petal formation and development in different pathways. This study offers a global survey of petal development in tree peony and will supply valuable information for future molecular studies of flowering development in tree peony.