Methylation Sensitive Amplified Polymorphism (MSAP) Analysis of DNA Epigenetic Changes of Cotton (Gossypium hirsutum L.) Cotyledons under Ethephon Treatment
Abstract：Leaf senescence affects the yields and fiber quality of cotton (Gossypium hirsutum L.), while ethephon is an important plant growth regulator, which plays important role in promoting the senescence of plant tissues. DNA methylation is an important component of the epigenetic regulation, and plays a very important role in the regulation of gene expression in higher plants. The methylation sensitive amplified polymorphism (MSAP) technique was used to assess epigenetic variations of cotton cotyledons under ethephon treatment, which would help to isolate and identify methylation regulating genes during cotton cotyledons senescence. The results showed that the cotton cotyledons genomic DNA methylation ratios were 32.99%, 35.45% and 37.49%, respectively, lower than that of the control group (37.92%), when they were treated with 300, 500 and 700 mg/L ethephon. In contrast with the control group, treated with 300, 500 and 700 mg/L ethephon, methylation and demethylation loci ratio of cotton cotyledons genomic DNA were 2.71%, 3.63%, 4.88% and 10.66%, 9.84%, 9.23%, respectively. The ratios of DNA methylation and demethylation increased gradually accompanied with the enhancement of ethephon treatment. Seventeen MSAP different fragments were identified, and NCBI Blast results showed that these different fragments were homologous to functional genes, including senescence-associated genes (such as pectin methylesterase gene), abiotic stress-related genes (such as cytochrome P450), signal transduction-related genes(such as alcohol dehydrogenase gene, cytoskeleton-related genes and actin depolymerizing factor), and protein synthesis-related genes(such as translation elongation factor 1A-1), which were associated with senescence of cotton cotyledons under ethephon treatment. In conclusion, in the ethylene-induced senescence course of cotton cotyledons, DNA methylation played an important role in the regulation of cotton cotyledons senescence, which provides a theoretical basis for regulation mechanism of cotton senescence from the genomic level.
