Abstract:

In this study, a full-length cDNA encoding PtSUS 1 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 PtSUS 1 shares 83.4％, and 75.7％ identity with Arabidopsis thaliana AtSUS 1 , and Oryza sativa OsSUS 1 , respectively. Tissue differential expression detected with Realtime-PCR indicated that the PtSUS 1 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 PtSUS 1 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 PtSUS 1 , of which 55, 10 and 1 are silent, missense, and nonsense mutations, respectively. In coding region of PtSUS 1 , the nonsynonymous nucleotide substitutions (π_nonsyn) was markedly lower than π_syn, with the π_nonsyn/π_syn ratio ＜ 1, suggesting that diversity at the synonymous sites of exon regions resulted from strong purifying selection.

Key words: Populus tomentosa, cellulose, sucrose synthase, phylogeny, single nucleotide polymorphisms