Promoters are key regulators of gene expression, and their sequences determine the specific expression levels of the associated genes. The level, location, and manner of gene expression are regulated by the promoter, so a thorough understanding of promoters is of great importance for understanding the expression patterns of corresponding genes.
Some genes encode important classes of transcription factors, which play crucial roles in developmental and regulation of multicellular eukaryotes. CUC2 is a gene which encodes the NAC domain transcription factor required for establishing boundaries around plant organ primordia. Recent studies have helped to clarify the relevant mechanisms in model plants (i.e., Arabidopsis thaliana, Solanum lycopersicum, Zea mays, and Medicago truncatula). However, because most tree genomes are generally larger and highly heterozygous and repetitive genomes, research into genes function of tree species has progressed slowly. Hence, the promoter and function of the birch BpCUC2 gene have not been fully characterized.
In this study, we constructed a pBpCUC2::LUC recombinant vector for birch transgenic using an agrobacterium-mediated transformation procedure and generated pBpCUC2::LUC transgenic birch plants, and analyzed LUC expression levels in the buds, leaves, stems, and roots using qRT-PCR. We observed that LUC was most highly expressed in the buds, which is consistent with the fact that CUC2 is a boundary-specific gene. We also found that our results were similar for Arabidopsis, as the AtCUC2 gene is also highly expressed in the apex, suggesting that BpCUC2 may have the same function in apical meristem as AtCUC2.
Additionally, a yeast one-hybrid system involving a birch cDNA library was used to identify the regulator that interacts with the auxin response element of the promoter. The regulation of the transcription factors is mainly divided into transcriptional regulation, post-transcriptional regulation, and post-translational regulation. Transcription factors bind to cis-acting elements in the promoter of specific genes. Identifying important cis-acting elements in the promoter of specific target genes is important for characterizing the regulation of gene expression levels and which is of transcriptional regulation.
Using a yeast one-hybrid assay, we screened for proteins that interact with the BpCUC2 promoter. We identified three development-related proteins including 14-3-3 protein, ribosomal protein L3 (RPL3) and soluble inorganic pyrophosphatase-like isoform X1. These genes were related to growth and development indicating that BpCUC2 may also be associated with growth and development in Betula platyphylla × Betula pendula.
The results of this study provide novel insights into birch BpCUC2 expression characteristics and the upstream regulatory genes and represent a solid foundation for future investigations of BpCUC2 functions.
These findings are described in the article Analysis of the promoter features of BpCUC2 in Betula platyphylla × Betula pendula, published in the journal Plant Cell, Tissue and Organ Culture (PCTOC). This work was led by Chaoyi Liu from Northeast Forestry University.