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 in Arabidopsis thaliana

Abstract

O_LISalicylic acid (SA) is an important signaling molecule of the plant immune system. C_LIO_LISA biosynthesis is indirectly modulated by the closely related transcription factors TGA1 (TGACG-BINDING FACTOR 1) and TGA4. They activate expression of SARD1 (SYSTEMIC ACQUIRED RESISTANCE DEFICIENT1), the gene product of which regulates the key SA biosynthesis gene ICS1 (ISOCHORISMATE SYNTHASE 1). C_LIO_LISince TGA1 interacts with the SA receptor NPR1 (NON EXPRESSOR OF PATHOGENESIS-RELATED GENES 1) in a redox-dependent manner and since the redox state of TGA1 is altered in SA-treated plants, TGA1 was assumed to play a role in the NPR1-dependent signaling cascade. Here we identified 193 out of 2090 SA-induced genes that require TGA1/TGA4 for maximal expression after SA treatment. One robustly TGA1/TGA4-dependent gene encodes for the SA hydroxylase DLO1 (DOWNY MILDEW RESISTANT 6-LIKE OXYGENASE 1) suggesting an additional regulatory role of TGA1/TGA4 in SA catabolism. C_LIO_LIExpression of TGA1/TGA4-dependent genes in mock/SA-treated or Pseudomonas-infected plants was rescued in the tga1 tga4 double mutant after introduction of a mutant genomic TGA1 fragment encoding a TGA1 protein without any cysteines. Thus, the functional significance of the observed redox modification of TGA1 in SA-treated tissues has remained enigmatic. C_LI SIGNIFICANCE STATEMENTPrevious findings demonstrating a redox-dependent interaction between transcription factor TGA1 and NPR1 attracted considerable attention. Here we show that TGA1 can act in the NPR1- and SA-dependent signaling cascade, but that its SA-regulated redox-active cysteines do not affect its function in this process.