Epigenetic mechanisms of salt tolerance and heterosis in Upland cotton ( Gossypium hirsutum L.) revealed by methylation-sensitive amplified polymorphism analysis

In order to explore the molecular mechanism of salt tolerance and heterosis in cotton, a methylation-sensitive amplification polymorphism method based on capillary electrophoresis was used to analyze DNA methylation level in a cotton hybrid CCRI 29 and its two parents. The major results and conclusions are as follows: Firstly, salt tolerance test showed that CCRI 29 had higher salt-tolerance level than its both parents. The global DNA methylation level in CCRI 29 under salt treatment significantly increased, whereas the two parents did not change significantly between salt treatment and control. All kinds of variation of DNA methylation happened in cotton under salt treatment, and hypermethylation happened at a significantly higher rate than that of hypomethylation in CCRI 29 but not in its two parents. The results suggested that the increase of global DNA methylation level in cotton genome and also different methylation types played an important role in tolerance to salt treatment in cotton. Secondly, both hypomethylation and hypermethylation happened to different genes and some genes maintained the same methylation level after salt stress, which meant that complex gene expression alterations occurred when responding to salt stress in cotton, indicating the complicated characteristics of roles that specific genes played in salt tolerance. Thirdly, although most cytosine methylation sites in hybrid CCRI 29 shared the same status as that of at least one of the parents, the site number of hypomethylation is significantly higher than that of hypermethylation in CCRI 29 compared to parents under both control and salt stress, indicating that demethylation could be the mechanism to explain heterosis in cotton hybrid.