TGACG‐BINDING FACTOR 1 (TGA1) and TGA4 regulate salicylic acid and pipecolic acid biosynthesis by modulating the expression of SYSTEMIC ACQUIRED RESISTANCE DEFICIENT 1 (SARD1) and CALMODULIN‐BINDING PROTEIN 60g (CBP60g)

Abstract

Summary Salicylic acid (SA) and pipecolic acid (Pip) play important roles in plant immunity. Here we analyzed the roles of transcription factors TGACG‐BINDING FACTOR 1 (TGA1) and TGA4 in regulating SA and Pip biosynthesis in Arabidopsis thaliana. We quantified the expression levels of SYSTEMIC ACQUIRED RESISTANCE DEFICIENT 1 (SARD1) and CALMODULIN‐BINDING PROTEIN 60g (CBP60g), which encode two master transcription factors of plant immunity, and the accumulation of SA and Pip in tga1‐1 tga4‐1 mutant plants. We tested whether SARD1 and CBP60g are direct targets of TGA1 by chromatin immunoprecipitation−polymerase chain reaction (ChIP‐PCR). In addition to promoting pathogen‐induced SA biosynthesis, we found that SARD1 and CBP60g also positively regulated Pip biosynthesis by targeting genes encoding key biosynthesis enzymes of Pip. TGA1/TGA4 were required for full induction of SARD1 and CBP60g in plant defense. ChIP‐PCR analysis showed that SARD1 was a direct target of TGA1. In tga1‐1 tga4‐1 mutant plants, the expression levels of SARD1 and CBP60g along with SA and Pip accumulation following pathogen infection were dramatically reduced compared with those in wild‐type plants. Consistent with reduced expression of SARD1 and CBP60g, pathogen‐associated molecular pattern (PAMP)‐induced pathogen resistance and systemic acquired resistance were compromised in tga1‐1 tga4‐1. Our study showed that TGA1 and TGA4 regulate Pip and SA biosynthesis by modulating the expression of SARD1 and CBP60g.

The potato transcription factor StbZIP61 regulates dynamic biosynthesis of salicylic acid in defense against Phytophthora infestans infection

“…These data indicate that SA biosynthesis is a dynamic and tempo‐spatially controlled process in plants. Recently, it was reported that two Arabidopsis bZIP transcription factors (TGA1 and TGA4) are involved in the regulation of SA biosynthesis (Sun et al ., ). In our study, we observed that expression changes in StbZIP61 were correlated with changes in StICS1 .…”

Redox-active cysteines in TGACG-BINDING FACTOR 1 (TGA1) do not play a role in salicylic acid- or pathogen-induced expression of TGA1-regulated target genes inArabidopsis thaliana

“…Likewise, SARD1 , which was slightly but significantly activated by TGA1/TGA4 in the absence of SA (Fig. 1) and after Psm infections (Sun et al ., 2018), contains a TGACGTCA motif at position - 212 bps. The G-box is significantly depleted in promoters being less activated in sid2 tga1 tga4 plants.…”

“…In order to address the question whether the disulfide bridge-forming cysteines of TGA1 that become reduced in SA-treated plants indeed play a role for accurate transcription of SA-responsive genes, we first tested SA-induced expression of SARD1 , which has been recently identified as a target gene of TGA1/TGA4 (Sun et al, 2018). However, in contrast to Psm infections, spraying with 1 mM SA resulted in TGA1/TGA4-independent SARD1 expression (Fig.…”

“…Since SARD1 expression is modulated by TGA1/TGA4 upon pathogen infection (Sun et al , 2018), we questioned whether under these conditions TGA1/TGA4 might act in concert with NPR1 and SA. We tested SARD1 expression eight hours after infection with Psm in the tga1 tga4 , tga2 tga5 tga6, npr1 and the sid2 mutants (Fig.…”

“…These are due to the reduced expression of the master regulator of SA and pipecolic acid biosynthesis, SARD1 (SAR DEFICIENT 1) in Psm -infected tga1 tga4 plants. Chromatin immunoprecipitation experiments confirmed SARD1 as a direct target gene of TGA1/TGA4 (Sun et al , 2018).…”