The Epigenetic Effects Of DNA Methylation On Growth And Wood Properties Of Larix Kaempferi

Japanese larch（Larix kaempferi）is one of the most important timber trees in China with superior performance of genotype on fast-growing at early ages,wood properties,resistance and wide adaptation.DNA methylation is an important source of heritable phenotypic variation in plants.DNA methylation plays an important role in plant development.This study was conducted in a provenance trial of Larix kaempferi constructed in Jianshi County,Hubei Province and 440 individuals were randomly selected as experimental population.DNA methylation in the genome of immature xylem were detected using methylation sensitive amplification polymorphism（MSAP）and the data of height and diameter at breast height in continuous years and the wood properties were collected,both of which were used to explore the epigenetic diversity,epigenetic structure,epigenetic differentiation in natural population and the effect of DNA methylation on height and diameter growth trajectories and wood properties.This study aimed at finding the DNA methylation markers that affect stem growth trajectories and wood properties,which would provide important reference for molecular marker-assisted breeding and exploring epigenetical mechanism of important quantitative traits.The results in this paper were as follows:1.The optimized MSAP system of Japanese larch based on capillary electrophoresis was determined: DNA template dosage 100 ng,primers 0.75 pmol·μL^-1,Mg2+ 2 mmol·L^-1,dNTP 0.375 mmol·L^-1 and exTaq DNA polymerase 0.05 U·μL^-1.28 pairs of selective primer combinations were screened,which contained few miscellaneous peaks,high polymorphism and strong signal intensity.The DNA methylation matrix with 4002 polymorphic CCGG sites were detected using these primer combinations.2.There was abundant epigenetic diversity in natural population.The epigenetic diversity indexs were significantly different among provenances.The ratios of external and internal cytosine methylation of CCGG were also significantly different among provenances,revealing the changing DNA methyaltion patterns.The AMOVA analysis revealed that there were significant epigenetic differentiation（Fst = 0.068,p <0.001）among provenances.A total of 3089 DNA methylation markers were detected to differentiate among provenances significantly,342 of which differentiated at moderate or moderate level.The abundant epigenetic diversity and epigenetic differentiation might play an important role in provenance adaption.3.Functional mapping of DNA methylation underlying stem wood growth trajectories.The growth curves of individuals were fitted by the logistic growth equation.The functional mapping model was used to analyze the effect of DNA methylation on growth trajectories of height and diameter.Based on SAD model,one DNA methylation marker was detected to influence the height growth trajectories,which belonged to the cross-type epigenetic effect marker.Based on the AR model,three DNA methylation markers were found to influence the diametergrowth trajectories,which belonged to the late or mixed eigenetic effect markers.These DNA methylation markers affecting the growth trajectories have epigenetic effect on heterochronic parameters,including the timing of maximum acceleration of growth,the timing of inflection,the time of deceleration of growth and the duration of linear growth.These effective DNA methylation markers would help tree breeders to select specific growth patterns to improve timber production and achieve greater economic benefits.4.Association analysis of DNA methylation and wood properties.361 DNA methylation markers were detected to be associated with chemical and physical traits based on GLM model.187 DNA methylation markers affected multiple phenotypic traits simultaneously.The ratios of the cell wall and cavity in early wood,the fiber length in early wood,the fiber length of late wood,latewood percentage and microfibril angle of early,which have positive correlations with each other,were under the control of the same DNA methyaltion markers.Some DNA methylation markers affected physical properties in earlywood or latewood independently,which indicated that the difference of wood properties in early and latewood was related with DNA methylation.Six DNA methylation markers were found to affect target traits of pulp timber improvement simultaneously,which provide important reference to pulp timber impovement.The divergence of high and low phenotype mean for the ratios of fiber length and width in earlywood,latewood percentage and the fiber length of latewood might be the result of changes of DNA methylation patterns responding to environmental changes.