Methylation sensitive amplified polymorphism (MSAP) reveals that alkali stress triggers more DNA hypomethylation levels in cotton (Gossypium hirsutum L.) roots than salt stress

Abstract

Cytosine-5 hypomethylation or hypermethylation have been shown to regulate plant development and abiotic stress-responsive genes expression. However, some combinatory stresses in plants like saline and alkaline could have varied responses that could contribute to their adaptive evolution trends. We evaluated root and leaf DNA methylation patterns of cotton in salt (S, 9:1 molar ratio of NaCl to Na2SO4, pH 6.96) and alkali (A, 9:1 molar ratio of NaHCO3 to Na2CO3, with higher pH 9.21) stresses using methylation sensitive amplified polymorphism (MSAP) method and found out that in general, demethylation events occurred more than methylation events in both leaves and roots samples. In addition, the total methylation variation frequency was only 1.38% in leaves and 2.2% in roots under salt stress. However, the alkali stress triggered more alterations and decreased the DNA methylation level significantly (P<0.05) compared to salt stress. This was up to 2.59% and 12.44% in the scored CCGG sites in leaves and roots, respectively. These results suggest that more adaptive and possibly complex gene expression alterations could be occurring in the tolerance of the cotton root in response to salt and alkali stresses coupled with DNA methylation alterations, although exclusion physiological mechanisms cannot be ruled out.