Figure 2.

Mutations in the DNA methylation maintenance system affect the maternal–paternal genome balance and seed size. (A) In female gametes (red), maternally expressed genes (red arrow), which often restrict seed growth, are hypomethylated and active whereas paternally expressed genes (blue), which often promote seed growth, are methylated and silenced. Reciprocally, in male gametes (blue), growth-promoting paternally expressed genes (blue arrow) are hypomethylated and active, whereas growth-restricting maternally expressed genes (red) are methylated and silenced. After fertilization, differential allele-specific gene expression persists in seeds (green), resulting in balanced maternal and paternal gene expression and normal-sized seeds. (B) If DNA methylation is impaired in male gametes, genes that are normally paternally silenced become active, causing excess expression of growth-restricting genes in seeds and decreased seed size. (C) If DNA methylation is impaired in female gametes, genes that are normally maternally silenced become active, causing excess expression of growth-promoting genes in seeds and increased seed size.