Objective To study the molecular characteristics and expression pattern of constitutive photomorphogenesis and dwarf of Phyllostachys edulis ( PeCPD ), a kind of the key rate-limiting enzymes in biosynthesis of brasinosteroids, aiming at revealing the role of PeCPD in regulating the rapid growth of bamboo shoots and the response to light induction and stresses.

Method Primers were designed based on the CPD homologous sequence of PH01003419G0030 in the Bamboo Genome Database (BambooGDB) and used for PeCPD cloning. The bioinformatics method was used for further analyses, including the gene structure, the cis-elements, the basic physicochemical properties and the conserved domains of the protein encoded by PeCPD , the evolutionary relationships, and the gene expression patterns in different tissues. Quantitative real-time PCR (qRT-PCR) method was used to analyze the gene expression in different height shoots and that in leaves and roots under the circadian rhythm light conditions and stresses of drought and cold.

Result  PeCPD , a homologous gene of CPD in Ph. edulis was obtained, which cDNA was 1 584 bp in full-length including 5' untranslated region (UTR) 110 bp, 3' UTR 64 bp and coding sequence (CDS) 1 410 bp. The corresponding genomic sequence to the CDS was 2 796 bp containing 6 exons and 5 introns. PeCPD encoded a 470 aa protein with a molecular weight of approximately 52.2 kDa and the theoretical isoelectric point of 9.063. At the same time, the upstream sequence of PeCPD (1 999 bp) was obtained, which was completely consistent with the sequence in the database. Besides the basic elements of the promoter, the upstream sequence of PeCPD also contained a variety of environmentally relevant action elements, such as LTR involved in low temperature response, MBS in response to drought, and light responsive elements (AE-box and TCT-motif). Phylogenetic analysis based on the CPD amino acid sequences showed that Ph. edulis was clustered together with the monocotyledon plants such as Oryza sativa, Zea mays, Setaria italica and Brachypodium distachyon , which was closed to B. distachyon . Expression pattern analysis based on the transcriptome data demonstrated that PeCPD expressed obviously different in the seven tissues of Ph. edulis , with the highest level in 20 cm shoot and the lowest in root. The result of qRT-PCR showed that the expression level of PeCPD in shoots increased with the increasing height of bamboo shoots, those in leaves under the circadian rhythm light conditions demonstrated an increasing trend in the daytime and a decreasing trend at night (darkness). Under both drought and cold stresses, the expression of PeCPD in leaves and roots all showed similar trends of rising at first and falling then.

Conclusion CPD homologous gene ( PeCPD ) is obtained from Ph. edulis . The PeCPD is constitutively expressed in Ph. edulis . Moreover, its expression level in shoots increases with the increasing height of bamboo shoots, which suggests that PeCPD may regulate the growth of bamboo shoots by participating in the biosynthesis process of brasinosteroids. The expression of PeCPD in leaves shows circadian rhythm changes, indicating that it may be involved in the photomorphogenesis of Ph. edulis. The expression changes of PeCPD under drought and low temperature stresses indicate that PeCPD is helpful to improve the ability of bamboo to adapt to stresses.