title: Extensive, clustered parental imprinting of protein-coding and noncoding RNAs in developing maize endosperm.
abstract: Although genetic imprinting was discovered in maize 40 years ago, its exact extent in the triploid endosperm remains unknown. Here, we have analyzed global patterns of allelic gene expression in developing maize endosperms from reciprocal crosses between inbreds B73 and Mo17. We have defined an imprinted gene as one in which the relative expression of the maternal and paternal alleles differ at least fivefold in both hybrids of the reciprocal crosses. We found that at least 179 genes (1.6% of protein-coding genes) expressed in the endosperm are imprinted, with 68 of them showing maternal preferential expression and 111 paternal preferential expression. Additionally, 38 long noncoding RNAs were imprinted. The latter are transcribed in either sense or antisense orientation from intronic regions of normal protein-coding genes or from intergenic regions. Imprinted genes show a clear pattern of clustering around the genome, with a number of imprinted genes being adjacent to each other. Analysis of allele-specific methylation patterns of imprinted loci in the hybrid endosperm identified 21 differentially methylated regions (DMRs) of several hundred base pairs in length, corresponding to both imprinted genes and noncoding transcripts. All DMRs identified are uniformly hypomethylated in maternal alleles and hypermethylated in paternal alleles, regardless of the imprinting direction of their corresponding loci. Our study indicates highly extensive and complex regulation of genetic imprinting in maize endosperm, a mechanism that can potentially function in the balancing of the gene dosage of this triploid tissue.
authors: State Key Laboratory of Agrobiotechnology and National Maize Improvement Center, Department of Plant Genetics and Breeding,  China Agricultural University, Beijing 100193,  People's Republic of China.
authors: Mei
authors: M
authors: Zhang
authors: Hainan
authors: H
authors: Zhao
authors: Shaojun
authors: S
authors: Xie
authors: Jian
authors: J
authors: Chen
authors: Yuanyuan
authors: Y
authors: Xu
authors: Keke
authors: K
authors: Wang
authors: Haiming
authors: H
authors: Zhao
authors: Haiying
authors: H
authors: Guan
authors: Xiaojiao
authors: X
authors: Hu
authors: Yinping
authors: Y
authors: Jiao
authors: Weibin
authors: W
authors: Song
authors: Jinsheng
authors: J
authors: Lai
mesh_terms: D000483:Alleles; D016000:Cluster Analysis; D019175:DNA Methylation / Q000235:genetics; D056625:Endosperm / Q000196:embryology* / Q000235:genetics*; D018745:Genome, Plant / Q000235:genetics; D018392:Genomic Imprinting / Q000235:genetics*; D007438:Introns / Q000235:genetics; D016366:Open Reading Frames / Q000235:genetics*; D022661:RNA, Untranslated / Q000235:genetics*; D015203:Reproducibility of Results; D003313:Zea mays / Q000196:embryology* / Q000235:genetics*
chemical_list: D022661:RNA, Untranslated