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Tobacco bZIP transcription factor TGA2.2 and related factor TGA2.1 have distinct roles in plant defense responses and plant development
Author(s) -
Thurow Corinna,
Schiermeyer Andreas,
Krawczyk Stefanie,
Butterbrodt Thomas,
Nickolov Kaloian,
Gatz Christiane
Publication year - 2005
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.2005.02513.x
Subject(s) - transcription factor , activating transcription factor 2 , biology , gene , sp3 transcription factor , tcf4 , genetics , gene silencing , promoter , gene expression , enhancer
Summary Salicylic acid (SA) is a crucial internal signaling molecule needed for the induction of plant defense responses upon attack of a variety of pathogens. Basic leucine zipper transcription factors of the TGA family bind to activating sequence‐1 (as‐1) ‐like elements which are SA‐responsive cis elements found in promoters of ‘immediate early’ and ‘late’ SA‐inducible genes. TGA2.2 constitutes the main component of tobacco as ‐1 ‐binding f actor‐1 (ASF‐1). TGA2.1, which differs from TGA2.2 by being able to activate transcription in yeast, constitutes a minor fraction of the complex. Both proteins interact with NPR1, a protein essential for SA inducibility of ‘late’ genes. Here we demonstrate using dsRNAi mediated gene silencing that reducing the amount of TGA2.2 and TGA2.1 correlates with a significant decrease in ASF‐1 activity and with a decreased inducibility of both ‘immediate early’ and ‘late’ genes. In contrast, reducing the amount of TGA2.1 alone had no effect on the expression of these target genes suggesting that TGA2.1 is dispensable for SA‐inducible gene expression from the as‐1 element. Expression of a TGA2.2 mutant unable to form heterodimers with the endogenous pool of TGA factors led to reduced SA‐inducibility of ‘immediate early’ gene Nt103, indicating that the native leucine zipper is important for the protein to act positively on transcription. Plants with reduced amounts of TGA2.1 developed petal like stamens indicating a regulatory role of TGA2.1 in defining organ identity in tobacco flowers. A model is suggested that unifies conflicting results on the function of tobacco TGA factors with respect to activation of the ‘late’ PR‐1a promoter.