Response And Methylation Analysis Of Different Cotton Varieties Under High Temperature Stress

In order to evaluate the heat tolerance of various upland cotton(Gossypium hirsutum L.)cultivars and to screen index for the assessment of heat tolerance,13 upland cotton genotypes were treated under high temperature condition in greenhouse during the flowering and boll-forming stage.Six indexes,such as pollen germination rate,style length,lint percentage,pregnant seed rate,boll weight and boll rate were measured.The heat tolerance of the tested cultivars was evaluated by the method of principal component analysis,hierarchical cluster analysis and stepwise regression analysis.As a result,13 cultivars of upland cotton were divided into three categories.The regression equation was established by stepwise regression analysis:D=0.145+0.180X1+0.400X3+0.229X4+0.125X5+0.095X6(R2=0.988).Within the equation,five agronomic traits,namely,lint percentage,boll weight,pregnant seed rate,boll rate and pollen germination rate were covered,which were related to the heat tolerance of upland cotton at flowering and boll-forming stage.The thermostability of 13 upland cotton cultivars tested by stepwise regression equation was the same as the results classified by the method of principal component analysis.As for the flowering and bollforming stage of upland cotton,five indexes mentioned above can be applied to assess the germplasm resources or lines for their heat tolerance.High temperature results in heat stress,which would affect the growth and development of cotton.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.In this study,the heat-tolerant cultivar Sumian 16 and the heat-sensitive cultivar Shi185 were applied as materials to study the DNA methylation of cotton before and after high temperature treatment.The methylation sensitive amplified polymorphism(MSAP)technique was used to study the variations of the DNA methylation level and methylation pattern of cotton leaves under heat stress.The results showed that the methylation level of heat-tolerant cultivar Sumian 16 and heat-sensitive cultivar Shi 185 was increased,and the semi-methylation rate of Sumian 16 was higher than that of full methylation,while Shi185 was just the opposite.The methylation and desmethylation of cotton were investigated at the same time,however,the heat-tolerant cultivar Sumian 16 was mainly expressed as being methylated and the demethylation was mainly occurred in the heat-sensitive cultivar Shi 185.The results indicated that high temperature could improve the methylation level of cotton,and the change of DNA methylation level and status was closely involved in cotton heat tolerance.