Abstract
The function of the bZIP transcription factors is strictly dependent on their ability to dimerize. Heterodimerization has proven to be highly specific and is postulated to operate as a combinatorial mechanism allowing the generation of a large variety of dimers with unique qualities by specifically combining a small set of monomers; an assumption that has not yet been tested systematically. Here, the interaction pattern and the transactivation properties of 16 Arabidopsis thaliana bZIPs are examined in transiently transformed Arabidopsis protoplasts to deliver a perspective on the relationship between bZIP dimerization and function. An interaction matrix of bZIPs belonging to the C, G, H, and S1 bZIP groups was resolved by Bimolecular Fluorescent Complementation (BiFC) coupled to quantitative flow cytometric analysis, while an extensive GUS reporter gene assay was carried out to determine the effect of different bZIP pairs on the expression of four different known bZIP-targeted promoters. Statistical data treatment and complementary bioinformatic analysis were performed to substantiate the biological findings. According to these results, the 16 bZIPs interact in three isolated networks, within which their members dimerize non-specifically and exhibit a significant level of functional redundancy. A coherent explanation for these results is supported by in silico analysis of differences in the length, structure and composition of their leucine zippers and appears to explain their dimerization specificity and dynamics observed in vivo quite well. A model in which the bZIP networks act as functional units is proposed.
Highlights
The regulation of the gene expression is essential for plant growth and differentiation, as it adjusts the proteome to varying needs in response to environmental and developmental cues
The subset of basic region/leucine zipper (bZIP) studied is composed by the C-bZIPs, the G-bZIPs (GBF1, GBF2, GBF3, bZIP16, and bZIP68), the H-bZIPs (Hy5 and HyH), and a subset of the S-bZIPs known as S1-bZIPs [11, 21]
The wider perspective on the bZIP dimerization and function suggests that Arabidopsis bZIPs operate as functional units
Summary
The regulation of the gene expression is essential for plant growth and differentiation, as it adjusts the proteome to varying needs in response to environmental and developmental cues. Due to the sessile nature of plants, development is especially shaped by the environment as an adaptive response, in contrast to buffered development in animals. Transcriptional control is one of the most important means for regulating gene expression, and in plants is especially complex, encapsulated by the significant expansion of their transcription factor families.
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