TGA5 acts as a positive and TGA4 acts as a negative regulator of ocs element activity in Arabidopsis roots in response to defence signals.

TGA/OBF family members are bZIP transcription factors that bind to the octopine synthase (ocs) element, a plant promoter sequence that has been strongly linked to defence/stress responses. Intron-containing hairpin (ihp) constructs were used to generate Arabidopsis lines with reduced expression of TGA4 and TGA5. No visible phenotypic differences were observed between ihpTGA and wild-type (WT) plants. However, the ihpTGA4 and ihpTGA5 plants had opposite affects on ocs element activity, with the ihpTGA4 lines enhancing, and the ihpTGA5 lines reducing, the response of an ocs element construct to the key defence signals, salicylic acid (SA) and H(2)O(2), in roots.