Studies On Inheritance And Variation Of DNA Methylation In Parents And F₁ Hybrids Of Lagenaria Siceraria. Var. Hispide

DNA methylation as an important epigenetic modification plays an important role in controlling gene expression and maintaining genomic stability in higher animals and plants. In many studies, it is found that disturbance of intrinsic DNA methylation's patterns may lead to abnormality of phenotype in organism, or lethality. On the other hand, the variation of specific methylation's pattern in plants may provide opportunity for species evolution, especially in plant. Because the variation of methylation's pattern in plant can usually transmit for descendants through miosis.Bottle gourd (Lagenaria siceraria. var. hispide) is one of the crops where the phenomenon of heterosis or hybrid vigor is mainly used in production. Nonetheless, the mechanism of heterosis in hybrids remains largely mysterious. In this study, three bottle gourd inbred lines were selected and were crossed with each other to produce two sets of reciprocal hybrids. Inheritance and variation of methylation level and pattern in these hybrids relative to their corresponding inbred parental lines were investigated by the methylation-sensitive amplified polymorphism (MSAP), so as to probe the distribution and rule of genomic DNA methylation in bottle gourd. It will be wished that may provide the basis of breeding F₁ hybrid. The main results were summeized as following:1. We used MSAP method to analyze the levels of DNA methylation in leaves of bottle gourd inbred lines and hybrids. In leaves the two sets of reciprocal hybrids(1×5, 5x1, 5x4, 4x5) showed lower values of relative level of cytosine methylation at CCGG sites than those of their corresponding mid-parent and no difference was observed between the cross directions within a given hyrid combination.2. Although in the majority of CCGG sites, DNA methylation showed Mendelian inheritance from parental lines to hybrids, alterations in methylation pattern were detected in all hybrids studied at certain frequencies, ranging from 7.24% to 7.85%. In addition, there were more alterations at loci inherited from the paternal than from the maternal origin. However, the variations of between the reciprocal cross have tiny difference.3. The hybridization-induced methylation alterations seemed to include both directed and random events, as while some alterations occurred in all F₁ hybrid individual plants tested, others occurred only in some individuals.4. Preexisting heterozygosity was ruled out as all tested individual plants from a given inbred line always showed the same methylation pattern.5. Some differential methylation sequences were sequenced and the results have not suggested the relationship between DNA methylation and heterosis.The above results suggest that, in bottle gourd, whereas cytosine methylation at the majority of genomic loci exhibited faithful transmission from parents to infra-specific hybrids, aleration in both level and pattern occurred in all studied crosses. These alterations might play a role in regulating differential gene expression in hybrids vs. inbred parental lines.