Review on gene imprinting during seed development

Imprinting is a mitotically stable epigenetic modification that results in functional non equivalency of both parental genomes following fertilization. The phenomenon in which a set of genes is expressed according to their parent of origin. Imprinting occurs primarily in the placenta of mammals and in the endosperm of flowering plants. Imprinting is implemented to allocate limited resources to the offspring over which both paternal and maternal parents are competing. Parental conflict hypothesis and Differential dosage hypothesis explains the origin of genome imprinting in endosperm. Inter genomic conflict is evolutionary driving force for the origin of imprinting according to parental conflict hypothesis where as relative dosage of the regulatory factors in the endosperm is driving force in differential dosage hypothesis. DNA methylation, histone modification and chromatin remodelling are the mechanisms of gene imprinting (Kohler and Molisch, 2010). Three types of gene imprinting are noticed i.e., allele specific, gene specific and genome wide imprinting (Garnier et al., 2008). More convincing evidence of imprinting operating in the endosperm came from chromosomal translocation studies in maize. Little is known of the molecular and genetic mechanisms responsible for the endosperm acting as a hybridization barrier in plants. Gene dosage and imprinting effects in the endosperm are currently considered the ‘gatekeepers’ of endosperm development. Conclusive evidence linking these processes with hybrid failure remains patchy. Analysis of the molecular mechanisms regulating endosperm development in hybrids reveal the parts played by maternal determinants and parental imprinting in this complex process.