Fig. 3. Marker gene expression in 35S::WUS-GR-expressing plants. (A) 35S::WUS-GR-expressing seedlings (lower left) show the same phenotype with inhibition of cotyledon expansion, root growth and greening as 35S::WUS; 35S::GUS-expressing seedlings (upper left) when germinated on dexamethasone containing medium, but not on control medium (lower right). (B) Longitudinal section through a GUS-stained CLV3::NLSGUS-expressing plant. Staining is restricted to the stem cells of the SAM, mirroring the CLV3 mRNA expression pattern (compare with Fig. 2I). (C-J) Light micrographs of GUS-stained and cleared seedlings. Seedlings in C,E,G,I were treated with mock solution for 2 days, while seedlings in D,F,H,J were induced with 5 µM dexamethasone for the same time. (C,D) After dexamethasone treatment of 35S::WUS-GR; CLV3::NLSGUS seedlings (D), strong ectopic GUS expression is observed in cotyledons (c), leaves (l) and hypocotyl (h), mainly associated with vascular strands, while expression is restricted to the stem cells of the SAM in uninduced seedlings (arrowhead, C). (E,F) No difference in the GUS staining pattern is observed between dexamethasone induced (F) and uninduced (E) 35S::WUS-GR; KNAT1::GUS-expressing seedlings. (G,H) No difference in the GUS staining pattern is observed between dexamethasone induced (H) and uninduced (G) 35S::WUS-GR; KNAT2::GUS-expressing seedlings, even though the first morphological effects of ectopic WUS activity on young leaves – reduced expansion of the lamina and upright position – are already visible (arrowhead). (I,J) Occasional ectopically staining cells are visible along the vasculature of the first pair of rosette leaves in dexamethasone-treated 35S::WUS-GR; CycB1;1::CDBGUS-expressing seedlings (arrowhead in J), which were never observed in mock-treated seedlings of the same genotype (arrowhead in I). Scale bars are 5 mm in A, 100 µm in B and 500 µm in C-J.