Heterologous expression of Populus euphratica CPD (PeCPD) can repair the phenotype abnormity caused by inactivated AtCPD through restoring brassinosteroids biosynthesis in Arabidopsis

To get insights into the functional difference of CPD (constitutive photomorphogenesis and dwarfism) between herb and woody plants, a full-length Populus euphratica L. cDNA homologous to Arabidopsis thaliana CPD (AtCPD), named PeCPD, was introduced to Arabidopsis thaliana cpd mutant (CM) and corresponding wild type (WT), resulting in a series of CM-PeCPD and WT-PeCPD transgenic lines. All the CM-PeCPD lines differentially displayed evident restoration in phenotype and fertility compared to cpd mutant, but still showed differences from WT in some respects. All the WT-PeCPD lines displayed obvious overexpression phenotype compared to WT plants. The transcription levels (TLs) of PeCPD in the CM-PeCPD lines were positively correlated, and that in the WT-PeCPD lines uncorrelated, with the level of their phenotype restoration/change. In the CM-PeCPD lines, the TLs of AtDWF4, AtBR6OX2 and AtTCH4 were negatively, and of AtBAS1 and AtSAUR-AC1 positively correlated with PeCPD TLs, whereas in the WT-PeCPD lines, their TLs were uncorrelated, and positively or negatively correlated to PeCPD TLs. The level of total endogenous BRs was basically negatively correlated to the level of phenotype restoration/change and PeCPD TLs in the PeCPD transgenic plants. The findings indicate that PeCPD also plays important role in regulation of plant growth and development through participating in BR biosynthesis.