(A) Induction of WUS expression in far-red light depends on phyA. (B) Growth in CO2-deficient environment does not affect light induced WUS expression in four day old seedlings, but inhibits the development of the first leaves unless 1% sucrose is added to the growth medium (C). Seedlings in (C) were grown in white light (150 µmol*m−2*s−1) and in absence of CO2 for 11 days. (D and E) Quantification of WUS expression by qRT-PCR in seven day old seedlings grown in darkness (gray), 150 µmol*m−2*s−1 white light (yellow) or darkness in the presence of 1% sucrose (hatched gray). Expression levels were normalized to PP2A expression. Error bars show standard error of the mean of two biological replicates. (F) The hy5 mutation does not affect light induction of WUS expression. Tissue specific activation of light signaling outside the SAM can induce WUS expression in the meristem (G) and photomorphogenic growth (H,J) in dark-grown seedlings. Constitutively active phyB Y276H was expressed under different promoters: AP19: pAt1g26680; AP20: pAt3g59270; AP21: pSUC2; AP22: pUBQ10; AP87: pCAB3; AP88: pML1. Two independent lines for each construct were quantified. (I) Phenotypic differences of pML1:PHYB Y276H lines correlate with the expression level of PHYB. Expression of endogenous PHYB was determined by using a primer pair annealing in the 3' UTR of PHYB. Expression levels were normalized to PP2A expression. pWUS:3xVENUS-NLS expression (A,B,F and G) and hypocotyl length (H) were quantified in four day old seedlings exposed to different growth conditions (gray = darkness, red = red light (30 µmol*m−2*s−1), far red = far red light (30 µmol*m−2*s−1), blue = blue light (30 µmol*m−2*s−1), yellow = white light (150 µmol*m−2*s−1), solid box = w/o sucrose, hatched box = w/ 1% sucrose).