Characterization Of Allelic Variants Induced By Asymmetric Cell Hybridization

Asymmetric somatic hybridization is an efficient method for crop breeding.With this method,our lab previously constructed a set of wheat introgression lines,and bred a wheat cultivar Shanrong 3(SR3).The introgression of a few exogenous chromatin fragments led to genome shock,and therefor induced genome-wide genetic variation.However,several fundamental questions of genetic variation,such as whether it occurs randomly,suffers from selection pressure,alter synonymous codon use bias(SCUB)remain to be studied.In this work,we addressed these questions by comparing the expressed sequence tags of SR3 and its parent wheat Jinan 177(JN177).1.High frequencies of nucleotide substitutions(single nucleotide polymorphism,SNP)and insertions and deletions(InDels)occurred in both coding sequences(CDS)and untranslated regions(UTR),with higher frequencies in CDS than in UTR.In comparison with UTR,CDS had lower frequencies of InDels with sizes of not 3N multiples,but similar frequencies of InDels with sizes of 3N multiples。The frequencies of InDels with sizes of 3N multiple were higher than those with adj acent sizes of not 3N multiples.The results indicate that asymmetric somatic hybridization induced genetic variation is suffered from selection pressure.2.Both SNP and InDel frequencies were comparable in genes mapped on chromosomes introgressed with and without exogenous fragments.InDel-flanking frequencies had more pronounced SNP frequencies,which was more remarkable in chromosomes introgressed with exogenous fragments.The results show that exogenous fragments does not promote the genetic variation in local chromosomes,but elevates SNP frequencies of InDel-flanking sequences.3.A subgenome had the highest SNP and InDel frequencies,but D subgenome had the lowest,and SNP frequencies were positively correlated with InDel frequencies.In seven allelic chromosomes,those with higher SNP frequencies had lower InDel frequencies,and SNP frequencies were negatively correlated with InDel frequencies,and the relative genetic variation was comparable among allelic chromosomes.The results indicate that there has asymmetric somatic hybridization induces different extents of genetic variation among subgenomes,but similar among allelic chromosomes.4.SCUB was different between SR3 and JN177,and driven by DNA methylation,SCUB was more different between the two cultivars.The results show that asymmetric somatic hybridization leads to the shift of SCUB.Above findings demonstrate that asymmetric somatic hybridization induced genetic variation is resulted form the whole genomic shock and the local chromosomal shock,which is a predetermined non-random event that is suffered from selection pressure.