title: Genomic imprinting, methylation and parent-of-origin effects in reciprocal hybrid endosperm of castor bean.
abstract: Genomic imprinting often results in parent-of-origin specific differential expression of maternally and paternally inherited alleles. In plants, the triploid endosperm is where gene imprinting occurs most often, but aside from studies on Arabidopsis, little is known about gene imprinting in dicotyledons. In this study, we inspected genomic imprinting in castor bean (Ricinus communis) endosperm, which persists throughout seed development. After mapping out the polymorphic SNP loci between accessions ZB306 and ZB107, we generated deep sequencing RNA profiles of F1 hybrid seeds derived from reciprocal crosses. Using polymorphic SNP sites to quantify allele-specific expression levels, we identified 209 genes in reciprocal endosperms with potential parent-of-origin specific expression, including 200 maternally expressed genes and 9 paternally expressed genes. In total, 57 of the imprinted genes were validated via reverse transcriptase-polymerase chain reaction sequencing, and analysis of the genomic DNA methylation distribution between embryo and endosperm tissues showed significant hypomethylation in the endosperm and an enrichment of differentially methylated regions around the identified genes. Curiously, the expression of the imprinted genes was not tightly linked to DNA methylation. These results largely extended gene imprinting information existing in plants, providing potential directions for further research in gene imprinting.
authors.affiliation: Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming 650201, China Graduate University of the Chinese Academy of Sciences, Beijing, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Xu
authors.affiliation: Key Laboratory of Tropical Plant Resource and Sustainable Use, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, 88 Xuefu Road, Kunming 650223, China Graduate University of the Chinese Academy of Sciences, Beijing, China.
authors.forename: Mengyuan
authors.initials: M
authors.lastname: Dai
authors.affiliation: Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming 650201, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Li
authors.affiliation: Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming 650201, China liuaizhong@mail.kib.ac.cn.
authors.forename: Aizhong
authors.initials: A
authors.lastname: Liu
mesh_terms: D002367:Ricinus communis / Q000196:embryology / Q000235:genetics*; D019175:DNA Methylation; D056625:Endosperm / Q000235:genetics*; D017343:Genes, Plant; D018392:Genomic Imprinting; D020641:Polymorphism, Single Nucleotide