Fig. 3. Cre-loxP-based system for mosaic expression. (A) The system was tested in plants containing heat-shock-inducible Cre recombinase (hsp18.2::Cre) and a reporter construct consisting of loxP-flanked uidA inserted between the 35S promoter and GFP (35S::lox-uidA-lox-GFP). After a brief heat shock, transient induction of Cre caused excision of uidA and GFP activation in random cells and their descendants. (B,C) Optical sections of GFP-expressing sectors (arrows) on the cotyledon epidermis (B) and in hypocotyls (C) were recorded 7 days after heat shock.