Knockout Analysis of Arabidopsis Transcription Factors TGA2, TGA5, and TGA6 Reveals Their Redundant and Essential Roles in Systemic Acquired Resistance

Abstract

Arabidopsis nonexpresser of pathogenesis-related (PR) genes (NPR1) is the sole positive regulator that has been shown to be essential for the induction of systemic acquired resistance. In npr1 mutant plants, salicylic acid (SA)-mediated PR gene expression and pathogen resistance are abolished completely. NPR1 has been shown to interact with three closely related TGA transcription factors-TGA2, TGA5, and TGA6-in yeast two-hybrid assays. To elucidate the biological functions of these three TGA transcription factors, we analyzed single and combined deletion knockout mutants of TGA2 , TGA5 , and TGA6 for SA-induced PR gene expression and pathogen resistance. Induction of PR gene expression and pathogen resistance by the SA analog 2,6-dichloroisonicotinic acid (INA) was blocked in tga6-1 tga2-1 tga5-1 but not in tga6-1 or tga2-1 tga5-1 plants. Loss of INA-induced resistance to Peronospora parasitica Noco2 cosegregated with the tga6-1 mutation in progeny of multiple lines that were heterozygous for tga6-1 and homozygous for tga2-1 tga5-1 and could be complemented by genomic clones of wild-type TGA2 or TGA5 , indicating that TGA2 , TGA5 , and TGA6 encode redundant and essential functions in the positive regulation of systemic acquired resistance. In addition, tga6-1 tga2-1 tga5-1 plants had reduced tolerance to high levels of SA and accumulated higher basal levels of PR-1 under noninducing conditions, suggesting that these TGA factors also are important for SA tolerance and the negative regulation of the basal expression of PR-1 .

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.…”

Negative Regulation of Systemic Acquired Resistance by Replication Factor C Subunit3 in Arabidopsis

“…All data were normalized with Actin1. The primers used for amplification of Actin1, PR1, and PR2 were described previously (Zhang et al, 2003). Infection of wild-type and mutant plants with H. a. Noco2 was performed on 2-week-old seedlings as described previously (Li et al, 1999).…”

“…It functions through associations with TGA transcription factors to regulate PR gene expression and pathogen resistance (Durrant and Dong, 2004). A triple knockout mutant of TGA2, TGA5, and TGA6 displayed compromised SAR responses and increased basal PR gene expression, suggesting that TGA transcription factors have both positive and negative roles in regulating PR gene expression and SAR (Zhang et al, 2003).…”

Molecular Genetics of Mosquito Resistance to Malaria Parasites

“…Increased SA concentrations cause a change in the redox balance, resulting in de-oligomerization of NPR1, which allows it to move into the nucleus (Mou et al 2003). Once there, it interacts with specific transcription factors (Despres et al 2000;Zhang et al 1999), which are required for activation of expression of certain SA-regulated defense genes (Zhang et al 2003). This process is reminiscent of the mammalian IκB/NFκB system and a similar mechanism in insects in which binding of IκB to NFκB holds it in the cytoplasm until an appropriate signal occurs, at which time the released NFκB translocates to the nucleus (Baeuerle and Baltimore 1996;Hoffmann 2003).…”