中文摘要：

利用RT-PCR方法,首次从毛白杨成熟木质部cDNA文库中分离出PtSUS1 cDNA全长,并进行了测序和序列分析。结果表明：克隆的毛白杨PtSUS1 cDNA片段总长为2703bp,基因内部含有完整的开放阅读框架,大小为2415bp,可编码长度为805个氨基酸残基的蛋白质,所推导的蛋白质氨基酸序列与拟南芥AtSUS1、水稻OsSUS1的蛋白质氨基酸序列同源性分别为83.4%,75.7%。组织特异性Realtime-PCR结果显示,PtSUS1在成熟木质部表达丰度最高,在成熟叶片、根部和正在发育的木质部表达丰度中等,在韧皮部和形成层有少量表达,在嫩叶与顶端分生组织中表达丰度最低。在此基础上,组合利用MEGA4.0和DnaSP4.50.4软件对毛白杨40株基因型个体的PtSUS1序列进行比对和分析,共检测到235个单核苷酸多态性（SNP）位点,SNP频率为1/25bp,多样性指数π为0.00924。在外显子区域,共检测到66个SNP位点,其中55个为同义突变,10个为错义突变,1个为无义突变。在编码区内,非同义突变与同义突变的比率〈1,这一结果显示在毛白杨物种演化过程中,纯化选择是PtSUS1基因内同义SNP位点主要的进化驱动力。

英文摘要：

In this study,a full-length cDNA encoding PtSUS1 was isolated from the cDNA library prepared from mature xylem zone of Populus tomentosa by the RT-PCR method.The cDNA is 2 703 bp in length with an open reading frame （ORF） which encodes a protein of 805 aa.The deduced protein sequence of the PtSUS1 shares 83.4% ,and 75.7% identity with Arabidopsis thaliana AtSUS1,and Oryza sativa OsSUS1,respectively.Tissue differential expression detected with Realtime-PCR indicated that the PtSUS1 transcripts were the most abundant mRNA products in mature xylem,medium in mature leaf,root,and developing xylem,scarcer in the phloem and cambium,and the scarcest detected in young leaf and apical shoot meristems.The genomic sequences of PtSUS1 in 40 individuals were aligned,compared and analyzed using the software of MEGA4.0 and DnaSP4.50.7.A total of 235 single nucleotide polymorphisms （SNPs） were detected and the frequency and diversity of SNPs were 1 /25 bp and 0.009 24,respectively.There were 66 SNPs detected in the coding regions of PtSUS1,of which 55,10 and 1 are silent,missense,and nonsense mutations,respectively.In coding region of PtSUS1,the nonsynonymous nucleotide substitutions （πnonsyn） was markedly lower than πsyn,with the πnonsyn /πsyn ratio 1,suggesting that diversity at the synonymous sites of exon regions resulted from strong purifying selection.