Localization of GUS activity in transgenic P. patens expressing PpPHO1;1, PpPHO1;2, and PpPHO1;3 promoter-GUS fusion constructs. A to C, PpPHO1;1 promoter activity in protonemata (A) and gametophore (C) for plants grown on +Pi medium and stained for 24 h and in protonemata of plants grown in −Pi medium and stained for 6 h (B). D to H, PpPHO1;2 promoter activity in protonemata (D) of plants grown on +Pi medium and stained for 24 h, and in emerging leaves (E), leafy gametophore (F and G), and rhizoids (H) for plants grown on +Pi medium and stained for 6 h. I to L, PpPHO1;3 promoter activity in protonemata of plants grown in +Pi medium (I) or −Pi medium (J) and stained for 6 h, as well as in emerging leaves (K) and leafy gametophores (L) of plants grown on +Pi medium and stained for 6 h. Bars = 100 μm (A, B, D, I, and J); 30 μm (E and K); 2 mm (C, F, and L); and 500 μm (G and H).