Flower and synergid cell-specific expression of CRP genes and the CRP4 promoter. (A) Semi-quantitative RT-PCR demonstrates expression of endogenous CRP genes (At3g49565, At4g09545) and CRP pseudogenes (At2g18042, At5g60978) in flowers but not in leaves. With the exception of the pseudogene At2g18042, which shows some reactivation in leaves in mutants defective in RNA-directed DNA methylation (dcl3, At3g43920; rdr2, At4g11130; nrpe1, At2g40030), none of the genes or pseudogenes are appreciably expressed in these mutants. Actin (At3g18780) is shown as a constitutively expressed control. (B) Photographs of ovules from transgenic Arabidopsis plants transformed with constructs containing CRP4-GFP (right) and GUS (left) reporter genes under the control of the CRP4 promoter. Expression occurs exclusively in the synergid cell region of the female gametophyte (arrows). Identical results were obtained in multiple independent transgenic lines obtained for each construct.