Abstract
BZR transcription factors play essential roles in plant growth and environmental stimuli, and they are also the positive regulators of Brassinosteroid (BR) signal transduction in diverse plants. In addition, BZR TFs, as crucial regulators of BR synthesis, may have multiple stress-resistance functions and their related regulatory mechanisms have been well illustrated in model plants. Here, we carried out a genome-wide identification of BZR members in Chinese pear (Pyrus bretschneideri) and identified 13 members. By comparative analysis in five Rosaceae genomes, BZR members in the pear genome may have undergone large-scale duplication events during evolution. Purifying selection played an important role in almost all of the orthologous and paralogous gene pairs. According to the expression analysis of the PbBZRs during fruit development, three PbBZRs were selected for detailed analysis. Transcriptional activation assays presented that PbBZR1 repressed the promoters of P. bretschneideri lignin biosynthetic genes, such as PbCES9, PbCOMT3, and PbHCT6. Our study traces the evolution of BZR gene family members in Rosaceae genomes and illustrates that the rates of gene loss and gain are far from equilibrium in different species. At the same time, our results suggest that PbBZR1 may be involved in the negative regulation of lignin biosynthesis.
Highlights
Brassinosteroids (BRs) refer to a class of plant-specific steroidal hormones, which play important roles in response to environmental signaling and regulate various growth and developmental processes, including root development, vascular-differentiation, vascular development and senescence, photomorphogenesis, and cell elongation (Clouse et al, 1996; Li and Chory, 1997; Ye et al, 2010; Clouse, 2011)
No systematic, in-depth study of the BZR gene family has been reported in five Rosaceae species, including F. vesca, P. mume, P. persica, P. communis, and P. bretschneideri
The chromosome numbers of F. vesca, P. mume and P. persica were 14, 16 and 16, respectively, while the chromosome number of both P. communis and P. bretschneideri was 34 (Shulaev et al, 2011; Zhang et al, 2012; Verde et al, 2013; Wu et al, 2013; Chagné et al, 2014), implying that the members of BZR gene family might have undergone an expansion corresponding to chromosome number variation
Summary
Brassinosteroids (BRs) refer to a class of plant-specific steroidal hormones, which play important roles in response to environmental signaling and regulate various growth and developmental processes, including root development, vascular-differentiation, vascular development and senescence, photomorphogenesis, and cell elongation (Clouse et al, 1996; Li and Chory, 1997; Ye et al, 2010; Clouse, 2011). PbBZR1 in Pyrus bretschneideri Fruit highly conserved N-terminal domain with DNA-binding activity in vitro and in vivo (He et al, 2005; Yin et al, 2005). The BZR1 DNA binding domain is the most conserved region of the BZR1 proteins and is encoded by the first exon of each gene (He et al, 2005). There is an atypical basic helix-loop-helix DNA binding motif at the N-terminal of BZR1 and BES1, which can bind to E-box (CANNTG) and BRRE (CGTGT/CG) elements, respectively (He et al, 2005; Yin et al, 2005)
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