Figure 3.

Examples of paternal- and maternal-enriched gene expression in early Arabidopsis embryogenesis. A to E, Expression of a paternally enriched gene (At3g28780) using GUS reporter after fertilization in the zygote. The At3g28780 promoter:GUS line showed pollen-specific expression (A), no detectable expression in the ovule before fertilization (B), and expression in the zygote after fertilization (C). No GUS expression was detected in the zygote (red outline) when this GUS reporter line was used as female parent and crossed with pollen from wild-type male parent (D). In the reciprocal cross (pollen from the GUS reporter line as male parent and wild-type female), the GUS expression was observed after fertilization in the zygote (E). The red star and red outline in C and E indicate GUS expression in the pollen tube and zygote, respectively. F to J, De novo expression of a maternally enriched gene (At4g07410) tagged with GFP in the zygote. The GFP reporter line showed no detectable expression in the pollen (F) or in the pollen tube (G) but showed expression in the female gametophyte (H). The inserts in G (1 and 2) showed 4′,6-diamino-phenylindole staining of sperm nuclei (1) but no GFP signal (2). The GFP signal was also detected in the unfertilized ovule and specifically in the embryo sac nuclei, namely, egg cell, two synergids, two polar nuclei, and three antipodals (embryo sac, yellow outline; H). When the pollen from the GFP reporter line (no detectable expression of GFP) was crossed with wild type as female, the GFP signal was observed in the zygote (yellow outline) and the endosperm nuclei (red stars; I). In the reciprocal cross where the pollen from wild type was crossed into transgenic reporter line as female, GFP expression was observed in the zygote (J). Bar = 0.05 mm (A–E, H, and I) and 0.01 mm (F, G, and J).