Angiosperm Flora of India

Homo- and heterodimers of tobacco bZIP proteins counteract as positive or negative regulators of transcription during pollen development

Publication Type:Journal Article
Year of Publication:2010
Authors:Iven, T, Strathmann, A, Böttner, S, Zwafink, T, Heinekamp, T, Guivarc’h, A, Roitsch, T, Dröge-Laser, W
Journal:The Plant Journal
Date Published:2010
ISBN Number:1365-313X
Keywords:auxin, bZIP transcription factors, invertase, Nicotiana, Nicotiana tabacum, NIN88, pollen development, tobacco

Expression of BZI-1ΔN, a dominant-negative form of the tobacco (Nicotiana tabacum) basic leucine zipper (bZIP) transcription factor BZI-1 leads to severe defects in pollen development which coincides with reduced transcript abundance of the stamen specific invertase gene NIN88 and decreased extracellular invertase enzymatic activity. This finding suggests a function of BZI-1 in regulating carbohydrate supply of the developing pollen. BZI-1 heterodimerises with the bZIP factors BZI-2, BZI-3 and BZI-4 in vitro and in planta. Whereas BZI-1 exhibits only weak activation properties, BZI-1/BZI-2 heterodimers strongly activate transcription. Consistently, approaches leading to reduced levels of functional BZI-1 or BZI-2 both significantly interfere with pollen development, auxin responsiveness and carbohydrate partitioning. In situ hybridisation studies for BZI-1 and BZI-2 confirmed temporal and spatial overlapping expression patterns in tapetum and pollen supporting functional cooperation of these factors during pollen development. Plants over-expressing BZI-4 produce significantly reduced amounts of intact pollen and are also impaired in NIN88 transcription and enzymatic activity. BZI-4 homodimer efficiently binds to a G-box located in the NIN88 promoter but exhibits almost no transcriptional activation capacity. As BZI-4 does not actively repress transcription, we propose that its homodimer blocks G-box mediated transcription. In summary, these data support a regulatory model in which BZI-4 homodimers and BZI-1/BZI-2 heterodimers perform opposing functions as negative or positive transcriptional regulators during pollen development.

Short Title:The Plant Journal
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