a, EIN3 specifically induces EBS-LUC and ERF5-LUC activities in WT protoplasts. b, C2H4 (10 p.p.m.) induces EBS-LUC activity in WT but not in ein2-1 protoplasts. c, WT MKK7 or MKK9 specifically enhances EBS-LUC activities in ctr1 protoplasts. d, Constitutively active MKK7a or MKK9a further enhances EBS-LUC activities in ctr1 protoplasts. Protein expression (MKK–MYC) is shown. Error bars, s.d. (n = 3). All experiments were repeated three times with similar results.