Arabidopsis thaliana class-II TGA transcription factors are essential activators of jasmonic acid/ethylene-induced defense responses

Abstract

SUMMARYThe three closely related Arabidopsis basic leucine zipper (bZIP) transcription factors TGA2, TGA5 and TGA6 are required for the establishment of the salicylic acid (SA)-dependent plant defense response systemic acquired resistance, which is effective against biotrophic pathogens. Here we show that the same transcription factors are essential for the activation of jasmonic acid (JA)-and ethylene (ET)-dependent defense mechanisms that counteract necrotrophic pathogens: the tga256 triple mutant is impaired in JA/ET-induced PDF1.2 and b-CHI expression, which correlates with a higher susceptibility against the necrotroph Botrytis cinerea. JA/ET induction of the trans-activators ERF1 and ORA59, which act upstream of PDF1.2, was slightly increased (ERF1) or unaffected (ORA59). PDF1.2 expression can be restored in the tga256 mutant by increased expression of ORA59, as observed in the tga256 jin1 quadruple mutant, which lacks the transcription factor JIN1/AtMYC2 that functions as a negative regulator of the JA/ET-dependent anti-fungal defense program. Whereas JA/ ET-induced PDF1.2 expression is strongly suppressed by SA in wild-type plants, no negative effect of SA on PDF1.2 expression was observed in the tga256 jin1 quadruple mutant. These results imply that the antagonistic effects of TGA factors and JIN1/AtMYC2 on the JA/ET pathway are necessary to evoke the SA-mediated suppression of JA/ET-induced defense responses.

Arabidopsis MYC Transcription Factors Are the Target of Hormonal Salicylic Acid/Jasmonic Acid Cross Talk in Response to Pieris brassicae Egg Extract

“…MAP KINASE4 is a negative regulator of the SA pathway and a positive regulator of the JA pathway (Petersen et al, 2000). Multiple TGA transcription factor mutants tga235 and tga2356 are blocked in SA-mediated inhibition of JA (Zander et al, 2010;Leon-Reyes et al, 2010b). For WRKY transcription factors, wrky50 and wrky51 mutants do not show SA suppression of JA-mediated PDF1.2 expression (Gao et al, 2011).…”

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

“…They mediate the induction of PR gene expression and SAR in response to biotrophic pathogens (Zhang et al 2003), and they are involved in the activation of detoxification responses after exposure to chemical stresses (Fode et al 2008;Mueller et al 2008). Furthermore, class II TGA factors were recently shown to modulate the ethylene and jasmonic acid-dependent responses to necrotrophic pathogens (Zander et al 2009). The same group of TGA transcription factors was shown here to be required for the induction of 250 of the 446 genes (56%) that were up-regulated after safener treatment in Arabidopsis (Fig.…”

Plant Immunity: It’s the Hormones Talking, But What Do They Say?

“…Unexpected connections between the gene regulatory networks of these factors start to emerge. For example, TGA transcription factors that were previously implicated in the regulation of SA-dependent defenses were also shown to be essential activators of induced defenses that are triggered by the combined action of JA and ET (Zander et al, 2009). However, upon simultaneous activation of the SA, JA, and ET pathways, TGAs act together with MYC2 to suppress JA/ETdependent defenses (Zander et al, 2009), again demonstrating the delicate interrelationship between these hormones.…”

“…For example, TGA transcription factors that were previously implicated in the regulation of SA-dependent defenses were also shown to be essential activators of induced defenses that are triggered by the combined action of JA and ET (Zander et al, 2009). However, upon simultaneous activation of the SA, JA, and ET pathways, TGAs act together with MYC2 to suppress JA/ETdependent defenses (Zander et al, 2009), again demonstrating the delicate interrelationship between these hormones. While the players in hormone cross talk become more and more identified, it is clear that various posttranslational protein modifications add to the complexity of the hormone-regulated immune signaling network (for review, see Spoel et al, 2010).…”

“…Many studies have demonstrated that endogenously accumulating SA antagonizes JA-dependent defenses, thereby prioritizing SA-dependent resistance over JA-dependent defense . ET often plays a modulating role in this respect , 2010Zander et al, 2009). However, depending on the plant species and strategy of the attacker, JA can also antagonize the SA pathway.…”