| Bread wheat(AABBDD)was originated from the diploid progenitors Triticum urartu(AA),Aegilops speltoides(BB)and Aegilops tauschii(DD).The DREB1 transcription factor plays key regulatory role in low temperature tolerance.The modern breeding strategies resulted in serious decrease of the agricultural biodiversity,which led to a loss of elite genes underlying abiotic stress tolerance in crop.However,natural diversity of this gene is largely unknown in the genome donor species of wheat.The information on genetic diversity not only has a significant genetic resource for crop improvement,but also provides guideance for the efficient conservation and utilization of genetic resources.This study analyzed the Dreb1 nucleotide sequences and haplotype diversity among Ae.speltoides,Ae.tauschii,T.monococcum and T.urartu,the evolution and origin of the wheat genome based on this gene sequnce.The main results of this study were as follows:1.The size of amplified DREB transcription factor polymorphisms was approximately 850 bp in the Aegilops speltoides(S genome),Ae.tauschii(D genome),Triticum monococcum(Am genome)and T.urartu(Au genome).Complete alignment of the 68 DREB1 sequences found a large size(70 bp)insertion/deletion in the accession PI486264 of Ae.speltoides.BLAST search against NCBI found that this sequences shared 100%identity with T.aestivum DREB transcription factor 6(DREB6)mRNA(AY781361.1),the sequences on T.aestivum chromosome 3B(LS992087)and T.aestivum genome B dehydration-responsive element-binding protein(DREB1)gene,partial cds(DQ195069.1).Blastx search found that protein sequence of this accession matched with dreb transcription factor 6(AAX 13289.1)in T.aestivum with 100%identity,while it lost"KDESESPPSLISNAPTAALHRSDA" when compared with AP2-containing protein in T.aestivum(AAL01124.1).Alignment of the 68 DREB 1 sequences found a large size(70 bp)insertion/deletion in the accession PI486264 of Ae.speltoides,which was different from the copy of sequences from other accessions of Ae.speltoides,suggesting likely existence of two different ancestral Ae.speltoides forms.Implication of sequences variation of Ae.speltoides on origination of B genome in wheat was discussed.So the accession PI486264 of Ae.Speltoides might be more likely the B donor genome of wheat.2.The highest nucleotide diversity values were detected in Ae.speltoides,followed by Ae.tauschii and T.monococcum.The lowest nucleotide diversity values were observed in T.urartu.The highest nucleotide diversity values(?=0.00456 ? ?=0.00685)were Ae.speltoides,higher than the other three nucleotides Ae.tauschii(?=0.00320 and ?=0.00281),T.monococcum(?=0.00301 and ?=0.00325)and T.urartu(?=0.00146 and ?=0.00173).This might attribute to the mating system of these species.Aegilops speltoides is an outcrossing species,while Ae.tauschii,T.monococcum and T.urartu are inbreeding species.Mating systems are one of the major factors controlling molecular diversity.3.The haplotypes of DREB1 sequences from Ae.speltoides,Ae.tauschii,T.monococcum and T.urartu were calculated.A total of 19 haplotypes were identified in the 68 accessions of these four species,which included 7,7,10 and 4 haplotypes from 13 sequences of Ae.speltoids,12 sequences of Ae.tauschii,24 sequences of T.monococcum,and 19 sequences of T.urartu,respectively.Twenty-six out of 68 accessions belonged to hap 2,and 15 of them belonged to the hap 7.For each species,most of the Ae.speltoides sequences belonged to Hap 2 with frequency of 0.538.The hap 2,hap 7 and hap 2 were the haplotype with highest frequency in Ae.tauschii,T.monococcum and T.urartu respectively.Thirteen haplotypes were species-specific,while two haplotypes(Hap 1 and Hap 7)were shared by Ae.speltoides,Ae.tauschii and T.monococcum,one(Hap 8)was shared by Ae.speltoides and T.monococcum,and one(Hap 10)was shared by Ae.tauschii and T.monococcum,only one haplotype(Hap 2)was shared among four species.Our result supported the conclusion on "no reduction of nucleotide diversity during T.monococcum domestication". |
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