Paternal genomic imprinting in plants

To screen for loci that are expressed during early ovule and seed development, Vielle-Calzada et al. used enhancer-detector lines that contain Ds mobile elements linked to a uidA gene, which encodes α-glucuronidase (GUS). They identified 19 lines that show GUS expression in the developing embryo and/or endosperm tissue after fertilization. To determine whether the expression pattern is the result of transcription from one or both of the parental alleles, reciprocal crosses were performed. When wild-type pollen was crossed to the transposant lines, all of the progeny showed GUS expression patterns identical to the self-fertilized transposant lines. In contrast, when transposant pollen was crossed to wild-type lines, GUS expression was undetectable. To confirm that the GUS expression pattern reflected the expression of endogenous genes, in situ hybridization was performed using an RNA probe specific for a gene tagged by one of the Ds elements in one transposant line. Additionally, to determine whether other genes that are expressed during early embryogenesis could have paternal allele silencing, single-nucleotide polymorphism (SNP) in the PROLIFERA (PRL) and EMB30/GNOM genes was exploited to detect allele-specific transcripts in whole siliques (seed pods) using reverse transcription polymerase chain reaction (RT-PCR). The assays showed that the transcripts from the maternal allele were present, but that transcripts from the paternal allele were not detectable.Enhancer and gene trap lines from a number of sources are available from the Arabidopsis Biological Resource Center (ABRC) through the Arabidopsis information management system and the Nottingham Arabidopsis Stock Centre. The Arabidopsis Information Resource provides access to approximately 39,000 SNPs and insertions/deletions (INDELs), including the Cereon Arabidopsis polymorphism collection generated by Cereon Genomics and SNP sequences generated by the Stanford Genome Center (GSC).This paper provides a fascina