The Chromatin Remodeler DDM1 Regulates The Segregation Ratio And Development In Arabidopsis Thaliana

According to Mendel's classical genetic law,the heterozygous F1 alleles have the same ability to transfer into F2 generation progenies through meiosis with a ratio of 1:2:1.Segregation distortion is common in most genetic mapping experiments and a valuable resource to find how gene loci induce deviation.The segregation distortion and plant developments are under the control of many epigenetic modifications.DNA methylation is an important epigenetic mark in plants that controls various functions,including gene expression and genome stability during plant growth and development.The DNA methylation is mainly regulated by the RdDM(RNA-directed DNA methylation)pathway;the chromatin remodeler factor DDM1(Decrease in DNA Methylation)is needed to silence the heterochromatic regions of the chromosome.In the present study,we are interested in exploring the relationship between segregation distortion and epigenetic modifications.The wild types Col/C24 and ddm1 mutants(ddm1-10(Col)and ddm1-15(C24))were reciprocally crossed to get the F2 generations.The 300 plants in the F2 generations of the reciprocally crossed progenies were used for resequencing to find the SNPs(single nucleotide polymorphisms)ratio,using the Chi-square test method.The whole-genome SNPs were divided into 16 classes due to their segregation ratio.The SNPs included in class 10,wild-types reciprocal crosses showed a 1:2:1 ratio,while the ddm1 mutants reciprocal crosses showed distortion.In class 16,regardless of wild types and mutants,all the SNPs showed a normal 1:2:1 ratio,and class1 showed segregation distortion using CAPS-marker analysis.In ddm1 mutants,the DNA methylation is highly abolished throughout the whole chromosome,more significantly in the heterochromatic regions.Our results confirmed that the ddm1-mutants have a low methylation level,which facilitated the segregation distortion of the SNPs mostly present in the heterochromatic region of the chromosomes.Further,the effect of ddm1 mutant on gene expression was explored.The results showed that the hypoDMRs in the promoter regions of DPA4(DEVELOPMENT-RELATED PCG TARGET IN THE APEX 4)directly affect the gene expression and control plant leaf serrations.The DPA4 acts as a negative regulator of the CUC2(CUP-SHAPED COTYLEDON2)transcription factor.The CUC2 promotes the generation of PIN1(PINFORMED1)-dependent auxin activity maxima and enhanced the leaf serrations.The low level of the CUC2 transcription factor produces smooth leaf margins.Our results showed that the ddm1-mutants exhibit low DNA methylation levels,which facilitates the segregation distortion of SNPs primarily located in the heterochromatic region of chromosomes by reducing the heterozygous ratio.Furthermore,the ddm1-mutant exhibited developmental and morphogenetic deficits through the activation of transposons and repeats.The present study will provide a strong base for future research that epigenetic marks control the segregation of traits and plant evolution.