ARF5 activates the Ipt promoter in an auxin-dependent manner.

(A) Fold induction of oncogene promoter-driven luminescence in Arabidopsis mesophyll protoplasts treated with auxin (1-NAA) or cytokinin (trans-zeatin) of different concentrations. Protoplasts were transfected with the IaaH, IaaM, and Ipt promoter-luciferase reporter constructs, and then incubated with different concentrations of 1-NAA or trans-zeatin overnight. (B) Fold induction of Ipt promoter-driven luminescence in Arabidopsis mesophyll protoplasts (Ipt pro) in the presence of the transcription factor expressing plasmids ARF5 (Ipt pro ARF5) or ARF5 plus IAA12 (Ipt pro ARF5 IAA12) with (+ 1-NAA) and without auxin (− 1-NAA) addition. (C) Mutations in the five auxin responsive elements (AuxREm, TGTCNC to TGGCNC and TGTCTN to TGGCTN) of the Ipt promoter abolish the ARF5- and auxin-dependent luminescence induction. The relative luminescence of intact or mutated Ipt promoters in the absence of any transcription factor expression plasmids and auxin treatment was set to 1. Bars show mean values (±SD) of three independent experiments. * P<0.05; ** P<0.01; *** P<0.001 (Student’s t-test).