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Homo‐ and heterodimers of tobacco bZIP proteins counteract as positive or negative regulators of transcription during pollen development
Author(s) -
Iven Tim,
Strathmann Anne,
Böttner Stefan,
Zwafink Thomas,
Heinekamp Thorsten,
Guivarc’h Anne,
Roitsch Thomas,
DrögeLaser Wolfgang
Publication year - 2010
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2010.04230.x
Subject(s) - transcription factor , nicotiana tabacum , biology , pollen , transcription (linguistics) , microbiology and biotechnology , tapetum , transcriptional regulation , regulation of gene expression , gene expression , gene , genetics , stamen , botany , microspore , linguistics , philosophy
Summary Expression of BZI‐1ΔN, a dominant‐negative form of the tobacco ( Nicotiana tabacum ) b asic leucine zip per (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.