Genetic Interactions of TGA Transcription Factors in the Regulation of Pathogenesis-Related Genes and Disease Resistance in Arabidopsis

Abstract

TGA transcription factors are implicated as regulators of pathogenesis-related (PR) genes because of their physical interaction with the known positive regulator, nonexpresser of PR gene1 (NPR1). A triple-knockout mutant tga2-1 tga5-1 tga6-1 was shown previously to be defective in the induction of PR genes and systemic acquired resistance, confirming their role in disease resistance. However, the contributions of individual TGA factors have been difficult to discern because of functional redundancy among these factors, as well as possible dual functions for some single factors. In this study, we characterized six TGA factors by reverse genetics. We show that TGA3 is required for both basal and 2,6-dichloroisonicotinic acid-induced transcription of PR genes. The tga3-1 mutants were found to be defective in basal pathogen resistance, whereas induced resistance was unaffected. TGA1 and TGA4 play partially redundant roles in regulation of basal resistance, having only moderate effects on PR gene expression. Additionally, an activation-tagged mutant of TGA6 was able to increase basal as well as induced expression of PR1, demonstrating a positive role for TGA6 on PR gene expression. In contrast, TGA2 has repressor activity on PR gene expression even though it can act as a positive regulator in the tga5-1 tga6-1 null mutant background. Finally, we examined the genetic interaction between tga2-2 and suppressor of npr1 inducible1 (sni1-1). TGA2's repressor activity overlaps with SNI1 because the tga2-2 sni1-1 double mutant shows a synergistic effect on PR gene expression.

The ROXY1 C-Terminal L**LL Motif Is Essential for the Interaction with TGA Transcription Factors

“…TGA transcription factors belong to a group of bZIP proteins that are categorized into 10 groups (A-I and S) in Arabidopsis. TGA transcription factors belong to group D, and all members of this group have been investigated (Running and Meyerowitz, 1996;Chuang et al, 1999;Jakoby et al, 2002;Zhang et al, 2003;Kesarwani et al, 2007;Murmu et al, 2010). Nuclear transcriptional coactivators of animals can contain one or more copies of the L**LL motif.…”

“…TGA transcription factors belong to the basic leucine zipper (bZIP) protein superfamily and comprise 10 members in Arabidopsis: TGA1 to TGA7, PERIANTHIA (PAN), TGA9, and TGA10 (Jakoby et al, 2002;Murmu et al, 2010). TGA1 to TGA7 are implicated as regulators of PATHOGENESIS-RELATED (PR) genes and hence disease resistance in Arabidopsis (Zhang et al, 2003;Kesarwani et al, 2007). Contrarily, PAN is involved in flower development, regulating the number of floral organ primordia.…”

Safeners recruit multiple signalling pathways for the orchestrated induction of the cellular xenobiotic detoxification machinery in Arabidopsis

“…To investigate a possible role of these TGA factors and to further substantiate the relevance of as-1-like elements in the regulation of the In2.1 promoter, we analysed the expression of the 0.8 kb promoter:reporter gene construct in a TGA factor-deficient Arabidopsis mutant. A quadruple mutant (tga2/3/5/6) was chosen for this experiment, which shows reduced background expression of the PR1 gene as compared with the tga2/5/6 triple mutant (Zhang et al 2003;Kesarwani et al 2007). The fold induction of GUS activity in safener-treated plants as compared with mock-treated controls was 33 times higher in the wild type than in the tga2/3/5/6 mutant background (Fig.…”

“…The tga2tga3tga5tga6 (tga2/3/5/6; Kesarwani, Yoo & Dong 2007) and sid2-2 (Nawrath & Metraux 1999) mutant seeds were kindly provided by Christiane Gatz (Georg-August-Universität Göttingen).…”

Data Integration and Knowledge Discovery in Life Sciences

“…The accumulation of SA is needed to trigger different signaling events, which can also be triggered by exogenous spraying of SA on the plants, even in the absence of pathogen. To help establish the role of various transcription factors involved in disease resistance [17,18] and the regulation of defense genes, a set of microarray experiments were conducted using four genotypes of Arabidopsis thaliana: Columbia wild-type Col-0, mutant npr1, double mutant in all Group I TGA factors, tga1 tga4, and triple mutant in all Group II TGA factors, tga2 tga5 tga6. Triplicate samples were collected before, 1 and 8 hours after SA treatment.…”