a, The expression of HD-ZIP III-target genes was measured using RT–qPCR in the apices of one-week-old zpr2-3 mutants and wild-type plants. These results show that the expression of five HD-ZIP III-target genes (PSK5, ATH1, ZPR1, AMP1 and POL) is significantly increased in zpr2-3 insertion mutants. Two-sided t-test; n = 10 plants. b, GUS expression under control of the MAX2 promoter in wild-type and zpr2-3-background genotypes. Restoration of wild-type background was obtained by PCR screening (for zpr2-3 insertion) and antibiotic resistance (for the pMAX2:GUS construct) in the F2 offspring of a cross between a pMAX2:GUS zpr2-3 plant and a wild-type (Col-0) plant. The observation was repeated twice. In total, the induction of pMAX2:GUS-GFP in zpr2-3 mutants was observed in 16 out of 20 plants. c, Hypothetical model describing how local hypoxia drives SAM activity by regulating HD-ZIP III transcription factors via ZPR2.