Abstract:

In this study, a fulllength cDNA clone encoding GA20Ox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 PsGA20Oxproteins shares 66.0% and 57.0％ identity with those of Arabidopsis thaliana and Oryza sativa, respectively. Tissue differential expression indicated that PsGA20Ox transcripts had their mRNA products in stems, leaves and apical shoot meristems, with different abundant in them. The PsGA20Ox 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 PsGA20Ox 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 PsGA20Ox, of which 23 were silent mutations and 3 were missense mutations. The linkage disequilibrium of SNPs in the PsGA20Oxwas detected and the result showed that LD declined rapidly within the gene regions of PsGA20Ox 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 PsGA20Ox gene and the geneassisted breeding in terms of growth and development in P. simonii.

Key words: Populus simonii, GA20 Oxidase, tissue differential expression with RT PCR, single nucleotide polymorphisms