TCP transcription factors are critical for the coordinated regulation of ISOCHORISMATE SYNTHASE 1 expression in Arabidopsis thaliana

Summary Salicylic acid ( SA ) plays an important role in various aspects of plant development and responses to stresses. To elucidate the sophisticated regulatory mechanism of SA synthesis and signaling, we used a yeast one‐hybrid system to screen for regulators of ISOCHORISMATE SYNTHASE  1 ( ICS 1 ), a gene encoding the key enzyme in SA biosynthesis in Arabidopsis thaliana . A TCP family transcription factor At TCP 8 was initially identified as a candidate regulator of ICS 1 . The regulation of ICS 1 by TCP proteins is supported by the presence of a typical TCP binding site in the ICS 1 promoter. The binding of TCP 8 to this site was confirmed by in vitro and in vivo assays. Expression patterns of TCP 8 and its corresponding gene TCP 9 largely overlapped with ICS 1 under pathogen attack. A significant reduction in the expression of ICS 1 during immune responses was observed in the tcp8 tcp9 double mutant. We also detected strong interactions between TCP 8 and SAR deficient 1 (SARD1), WRKY family transcription factor 28 (WRKY28), NAC (NAM/ATAF1,ATAF2/CUC2) family transcription factor 019 (NAC019), as well as among TCP 8, TCP 9 and TCP 20, suggesting a complex coordinated regulatory mechanism underlying ICS 1 expression. Our results collectively demonstrate that TCP proteins are involved in the orchestrated regulation of ICS 1 expression, with TCP 8 and TCP 9 being verified as major representatives.