Abstract
Plant bZIP group I transcription factors have been reported mainly for their role during vascular development and osmosensory responses. Interestingly, bZIP29 has been identified in a cell cycle interactome, indicating additional functions of bZIP29 in plant development. Here, bZIP29 was functionally characterized to study its role during plant development. It is not present in vascular tissue but is specifically expressed in proliferative tissues. Genome-wide mapping of bZIP29 target genes confirmed its role in stress and osmosensory responses, but also identified specific binding to several core cell cycle genes and to genes involved in cell wall organization. bZIP29 protein complex analyses validated interaction with other bZIP group I members and provided insight into regulatory mechanisms acting on bZIP dimers. In agreement with bZIP29 expression in proliferative tissues and with its binding to promoters of cell cycle regulators, dominant-negative repression of bZIP29 altered the cell number in leaves and in the root meristem. A transcriptome analysis on the root meristem, however, indicated that bZIP29 might regulate cell number through control of cell wall organization. Finally, ectopic dominant-negative repression of bZIP29 and redundant factors led to a seedling-lethal phenotype, pointing to essential roles for bZIP group I factors early in plant development.
Highlights
Transcription factors (TFs) represent one of the most for 9% of the protein-encoding gene pool
To investigate the spatio-temporal expression pattern of bZIP29 during plant development, 2 kb upstream of the start codon was used as the promoter fragment to drive the expression of a green fluorescent protein (GFP)–β-glucuronidase (GUS) reporter
BZIP29 showed very specific expression patterns (Fig. 1), mainly restricted to proliferative tissues, while no expression was detected in vascular tissues. bZIP29 was highly expressed in the root meristem of the primary root (Fig. 1A)
Summary
Transcription factors (TFs) represent one of the most for 9% of the protein-encoding gene pool TFs are mostly classified according to their model plant Arabidopsis thaliana (Arabidopsis), TFs account DNA-binding domains. The eukaryotic kingdom is characterized by the presence of a basic region–leucine zipper (bZIP) domain. The basic region binds DNA, while the leucine zipper motif is required for dimerization. During plant evolution, this family of TFs has expanded greatly. In Arabidopsis, 75 bZIP TFs have been identified, which were clustered into subgroups based on sequence similarity in their basic region and the presence of additional conserved motifs (Jakoby et al, 2002). Up to 82 bZIP TFs are present in Arabidopsis (Qu and Zhu, 2006), being involved in a plethora of biological processes (Alves et al, 2013; Llorca et al, 2014)
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