a, Effect of ZPR2 and ZPR2–GUS on the transactivation activity of REV on the ZPR1 promoter. These data indicate that ZPR2 is not able to repress REV activity when fused with a GUS reporter protein at its C terminus. One-way ANOVA, followed by Holm–Sidak post hoc test; n = 5 protoplast pools. b, Schematic of the construct that provided oestradiol-inducible expression of ZPR2, and after protein stabilization under hypoxic conditions. c, Separate and combined effect of oestradiol (50 μM) application, for 4 h before exposure to 2% O2 for 24 h, on the expression of a GUS reporter under the control of pHEC1 (HECATE 1) and pPSK5 (PHYTOSULFOKINE 5 PRECURSOR) promoters in 6-day-old Arabidopsis seedlings that also expressed an oestradiol-inducible ZPR2 construct. Seeds of these genotypes were obtained as F1 offspring that were generated by crossing homozygous promoter:GUS lines with homozygous oestradiol-inducible ZPR2 (pMDC7:ZPR2) plants. The observation was repeated twice. A reduction in pPSK5 or pHEC1 activity by combined ZPR2 induction and hypoxia was observed in a total of 8 out of 12 and 15 out of 20 plants, respectively. d, Effect of oestradiol-mediated induction of ZPR2 and its stabilization by hypoxia on pTAA1:GUS staining in five-day-old wild-type and transgenic pMDC7:ZPR2 plants. Twenty-four hours of hypoxia, but not oestradiol treatment (50 μM), was sufficient to repress pTAA1-driven GUS expression in the wild-type background, probably via stabilization of the endogenous ZPR2 protein (2 out of 3 plants). The hypoxia treatment also inhibited expansion of the first pair of true leaves. Stimulated ZPR2 expression in the pMDC7:ZPR2 background further decreased pTAA1:GUS staining (3 out of 3 plants). This experiment was performed once.