Fig. 4. Mosaic WUS expression combined with STM-GR activation caused ectopic organogenesis. (A) Control seedling (35S::lox-uidA-lox-GFP; hsp18.2::Cre) with no morphological effects 7 days after heat shock induction of GFP sectors (see Fig. 3). Inset: top view of comparable seedling. (B) Phenotype caused by mosaic WUS expression in 35S::lox-uidA-lox-WUS; hsp18.2::Cre seedlings, 7 days after heat shock. Inset: top view of similar seedling. (C,D) Phenotype after induction of mosaic WUS expression and STM-GR activation, in 35S::lox-uidA-lox-WUS; hsp18.2::Cre; 35S::STM-GR seedlings grown on medium with 1 µM dexamethasone 10 days after heat shock. The arrows indicate ectopic organs on the hypocotyl (C) and cotyledons (D). (E-H) Cryo-scanning electron micrographs of hypocotyls. (E) Hypocotyl from a control seedling as in A; (F) hypocotyl after WUS induction as in B; (G) example of outgrowth (arrow) observed on the hypocotyl at low frequency 2 weeks after WUS induction as in B; (H) hypocotyl after activation of STM-GR but not WUS (35S::STM-GR seedling grown for 10 days on medium with 1 µM dexamethasone). Bar: 100 µm. (I-K) Cryo-scanning electron micrographs of ectopic organs induced by combined WUS and STM-GR activation (as in C,D). (I) Outgrowth on cotyledon (as in D); (J,K) outgrowths on hypocotyls (as in C). Arrows in K indicate outgrowths at early stages. Bar: 100 µm.