Analysis of the tomato Pht1 gene promoters. (A) Comparative analysis of putative cis-regulatory elements responsible for the Pi- and AM-regulated expression between the eight tomato Pht1 promoters. Two previously reported Pi-responsive motifs (P1BS and W-box) and one AM-activated motif (MYCS) were searched using the DNA-pattern matching arithmetic (http://rsat.ulb.ac.be/rsat/). P1BS, GNATATNC; MYCS, TTCTTGTTC; W-box, TTGACY. (B) Histochemical analysis for the promoter activity of the two AM-induced Pht1 members, LePT3 and LePT5. (a-d) Localization of β-glucuronidase (GUS) activity (a and b, Magenta GUS; c and d, blue GUS) in mycorrhizal roots driven by the promoters of LePT3 (a, c) and LePT5 (b, d), respectively. (e, f) Co-localization of GUS activity (indicated by the purple color, from the overlay of the Magenta-GUS and Trypan Blue stains) showed that the LePT3and LePT5 promoter fragments (pLePT3
) were sufficient to direct GUS expression in mycorrhizal roots and were confined to distinct cortical cells containing AM fungal structures (arbuscules or intracellular hyphae). Green arrows indicate arbuscule or arbusculate hyphae, yellow arrows indicate intracellular hyphae and red arrows indicate noncolonized cells.