Imprinting is an epigenetic phenomenon referring to allelic-biased expression of certain genes depending on their parent-of-origin.Accumulated evidence suggests that while imprinting is a conserved mechanism across organismal kingdoms,the imprinted genes are largely species-specific.By using deep RNA sequencing of endosperm 14 days after pollination(DPA)in sorghum,5,683 genes(29.27%of the total 19,418 expressed genes)were found to harbor diagnostic single nucleotide polymorphisms(SNPs)between two inbred lines.The analysis of parent-of-origin expression patterns in endosperm of a pair of reciprocal F1 hybrids parented by the two inbred lines led to the identification of 101 genes with ≥ 5-fold allelic expression difference in both reciprocal hybrids,which included 85 maternal expressed genes(MEGs)and 16 paternal expressed genes(PEGs).Thirty-two of these genes were previously identified as imprinted in endosperm of maize,rice or Arabidopsis,while the remaining 69 genes are sorghum-specific imprinted genes relative to these three plant species.Allele-biased expression of nearly all 14 tested imprinted genes(nine MEGs and five PEGs)were validated by pyrosequencing using independent sources of RNA from different developmental stages and dissected parts of endosperm.Forty-seven genes(31 MEGs and 16 PEGs)were assayed by qRT-PCR,and almost all showed endosperm-specific or preferential expression relative to embryo and vegetative tissues.DNA methylation analysis of 5-upstream and gene-body for seven imprinted genes(three MEGs and four PEGs)indicated that while three of the four PEGs were associated with hypomethylation of maternal alleles,no MEG was associated with allele-differential methylation.