Figure 6.
APB Motif Activity Is Necessary for PIF4 Function.
The srl2 mutant lines transformed with the PIF4:PIF4 full-length gene containing either wild-type APB [shown in red; PIF4 FL(1) and PIF4 FL(2)] or mutated APB [G35A shown in blue; PIF4 FL(G35A-1), PIF4 FL(G35A-2), and PIF4 FL(G35A-3)].
(A) Stick diagram showing the PIF4 promoter (2 kb upstream of the ATG) and the PIF4 gene used for transformations of srl2 mutant lines (position of srl2 T-DNA insertion in relation to the NLS and the bHLH is indicated).
(B) Fluence rate response curves of mean hypocotyl lengths of wild-type (Ws), srl2 mutant, and indicated transgenic lines grown in Rc for 3 d. The phyB (Col) was used as a control.
(C) Seedling photomorphogenic phenotypes of srl2 mutant seedlings grown in Rc (17.8 μmol m−2 s−1) for 3 d are rescued by the PIF4 FL(2) transgene, are overcompensated in PIF4 overexpressing transgenic line PIF4 FL(1), and are not rescued in PIF4 FL(G35A) transgenic lines.
(D) Measurements of cotyledon area expansion in transgenic seedlings. The srl2 mutant seedlings grown for 3 d under Rc (17.8 μmol m−2 s−1) have enlarged cotyledon areas compared with the Ws (wild type), and this response is rescued (cotyledon expansion similar to the wild type) in the PIF4 FL(2) transgenic seedlings. The PIF4 FL(1) overexpressors show reduced cotyledon expansion; by contrast, all of the lines expressing mutated APB (G35A) have enlarged cotyledons compared with Ws. PhyB (Col) is shown for comparison. Approximately 20 to 25 seedlings for each line were used for measurements (40 to 50 cotyledons), and the values were normalized to Ws.