中文摘要：

利用RT-PCR方法,首次从小叶杨未成熟木质部cDNA中分离出PsGA20OxcDNA全长及其基因组DNA,并进行测序和序列分析。结果表明：克隆的小叶杨PsGA20OxcDNA片段总长为1403bp,基因内部含有完整的开放阅读框架,大小为1155bp,编码区可编码长度为385个AA残基,所推导的蛋白质氨基酸序列与拟南芥和水稻GA20Ox蛋白的同源性分别为66.0%和57.0%。组织特异性RT-PCR结果显示,PsGA20Ox基因在杨树茎、叶片和顶端分生组织中均有表达,但其表达模式却不同：PsGA20Ox在成熟木质部中表达丰度最高,在未成熟木质部和嫩叶中表达丰度较高,在顶端分生组织中有少量表达,在形成层组织中表达丰度极低。在此基础上,组合利用MEGA4.0和DnaSP4.50.4软件对小叶杨36株基因型个体的PsGA20Ox基因组DNA序列进行比对和分析,检测到49个单核苷酸多态性（SNP）位点,频率为1/35bp。其中,15个是常见SNPs,34个为罕见SNPs。在这些SNPs中,37个属于转换,12个属于颠换。在外显子区域,共检测到26个SNP位点,其中23个为同义突变,3个为错义突变。对PsGA20Ox基因内SNPs进行的连锁不平衡分析表明,随着核苷酸序列长度的增加,SNPs的连锁不平衡在基因内部就迅速衰退,因此,在小叶杨中,基于候选基因的连锁不平衡作图是可行的,而基于整个杨树基因组的连锁不平衡作图是不可行的,也是不必要的。

英文摘要：

In this study, a full-length cDNA clone encoding GA2OOx was isolated from the cDNA prepared from immature xylem zone of Populus simonii by the RT-PCR method. The cDNA is 1 403 bp in length with an open reading frame （ORF） which is capable of encoding a protein of 385 AA. The deduced aa sequence of the PsGA2OOx proteins shares 66.0% and 57.0% identity with those of Arabidopsis thaliana and Oryza sativa, respectively. Tissue differential expression indicated that PsGA2OOx transcripts had their mRNA products in stems, leaves and apical shoot meristems, with different abundant in them. The PsGA2OOx transcripts were the most abundant in mature xylem, followed by in the immaturity xylem and young leaf, and then in apical shoot meristems and the lowest transcripts were found in cambium. The genomic sequences of PsGA2OOx in 36 individuals were aligned, compared and analyzed using the software MEGA4.0 and DnaSP4.50.4. A total of 49 SNPs were detected and the frequency was 1/35 bp. Of the 49 SNPs, there were 15 common SNPs and 34 rare SNPs. There were 37 transition and 12 transversion mutation types. A total of 26 SNPs were detected in the coding regions of PsGA2OOx, of which 23 were silent mutations and 3 were missense mutations. The linkage disequilibrium of SNPs in the PsGA2OOx was detected and the result showed that LD declined rapidly within the gene regions of PsGA2OOx with the nucleotide length. It suggests that in Populus genome wide LD mapping may not be feasible and not be necessary, but candidate gene based LD mapping could be particularly useful in breeding programs of forest trees. The results, therefore, provided the important knowledge for the associated genetics of PsGA2OOx gene and the gene-assisted breeding in terms of growth and development in P. simonii.