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. 2011 Jun 23;7(6):e1002125. doi: 10.1371/journal.pgen.1002125

Figure 1. Seed development and imprinting in rice seeds.

Figure 1

(A) A cartoon showing parental contributions to embryo and endosperm tissues following double fertilization in rice ovules. In the triploid endosperm the maternal (m) to paternal (p) genome ratio is 2∶1 and in the diploid embryo a 1m∶1p ratio is observed. (B–D) Sections of developing rice seeds at indicated days after fertilization (DAF) showing embryo (em) and endosperm (en) morphology and the proximity of these tissues. Embryo differentiation is complete 10 DAF. Starch and protein accumulation continue in the endosperm until grain maturation (∼20–25 DAF). Endosperm was harvested for transcriptome analyses at 5 DAF and embryos at 6 DAF. Scale bars are all 100 µm. (E) Os10g05750 is a maternally expressed gene found in the embryo and endosperm. RT-PCR sequencing chromatographs show that maternal expression is maintained during endosperm development. In the embryo imprinting is transient as bi-allelic expression is evident at 8 and 10 DAF in the Nip (m)×93-11 (p) cross (arrows indicate double peaks for G and A). Some paternal expression is evident in the embryo at 10 DAF in the 93-11 (m)×Nip (p) cross. Os10g05750 is expressed in a range of other plant tissues (Figure S6). (F) Temporal changes in imprinting status for four endosperm imprinted genes. The bars provide a schematic representation of the relative expression levels of maternal (m; red) or paternal (p; blue) alleles for the four genes based on RT-PCR sequencing chromatographs (Figure S3). Dotted bars indicate low level of expression. All four genes become uniparentally expressed. Expression in sperm cells is indicated by (+), absence by (−) and (?) indicates uncertain from microarray analyses in triplicate (see Materials and Methods). (G) Allele specific RT-PCR confirming the dynamics of imprinting for Os02g55560 in endosperm obtained from reciprocal crosses between Nip and 93-11. The RT-PCR products were cut with EcoRV. The Nip+93-11 lane is a digestion control containing equal amounts of parental Nip and 93-11 RT-PCR products.