| DNA methylation plays an important regulating role in gene expression during growth and development in eukaryotes. A modified AFLP technique (methylation-sensitive AFLP, MSAP) was used in this study to detect the DNA methylation patterns in the 5'-CCGG sites of three sorghum hybrids, two corn hybrids and their parents, in the hope of understanding the molecular basis of heterosis in F1 generation. The results demonstrated that: 1. The MSAP ratio, which is the ratio of MSAP sites to the totally amplified sites, in three sorghum hybrids (V4A×1383, Tx622A×Jinliang5, and V4A×Jinliang5) and two corn hybrids (MO17×Suwan5, and Suwan1×Tai3221) were 48.7%, 47.6%, 41.8%, 39.15 and 40.1%, respectively, all of which were lower than those of either their parents. The MSAP ratio in 4 sorghum parents (V4A, 1383, Tx622A and Jinliang5) and 4 corn parents (MO17, Suwan5, Suwan1, and Tai3221) were 51.4%-61.3% and 39.7%-44.2%. Full methylation (5'CmCGG in double strands) levels were 27.7%, 25.4% and 28.0% in 3 sorghum F1s, which were lower than those of both their parents, suggesting demethylation was occurred in some amplified 5'CCGG sites, and 24.4% and 23.3% in two corn F1s, which were between their parents or equal to the high value parent. 2. Four classes of MSAP patterns, A, B, C and D, among 3 sorghum hybrids, two corn hybrids and their parents were detected: Pattern A, methylation levels were not changed in both parents and F1; Pattern B, demethylation, both or one of the parent was methylated, but no methylation in the same site in F1; Pattern C, hypermethylation, the methylation level in F1 was higher than those in both parents; Pattern D, hypomethylation, methylation in F1 was lower than those in both parents. 3. When two parents were hybridized, the patterns in F1 has changed and tuned greatly to coordinate the expressions of genes from two heterogeneous parents. Some genes transcribed high efficiently, but the transcription of other genes was restrained in F1s. The lowered methylation level in F1 compared to its parents was the balanced result after the methylations were readjusted and changed. The heterosis in F1s was associated with change and readjustment of methylation in sorghum and corn genomes. The utilization of heterosis in sorghum benefited greatly from the discovery of cytoplasmic-male sterility (CMS) of the crop. Seven kinds of CMS have been identified in sorghum, including A1, A2, A3, A4, A5, A6, and 9E, but only A1(milo) CMS has been widely used in commercial sorghum hybrid production. In this study we investigated the cyto-anatomy in anther development, the chromosomal behavior during meiosis in A2 and A3 CMS.and the genetic mechanism of fertility restoration in A2 CMS. The results were as follows: 1. Many abnormal phenomena were observed in tapetum cells in A2 CMS anther development: No tapetum cells were formed or they collapsed at very early stage during the microsporogenesis; Tapetum...
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