Abstract:

Abstract: The Wuschel (Wus) encoding a homeodomain protein which presumably acts as a transcriptional factor plays a key role in maintaining a pool of pluripotent stem cells. In this study, 2 putative sequences of Wus were identified in the whole genome of Populus by underlying the electronic cloning technique, based on the Populus genome sequence using Arabidopsis Wus gene sequence information. Two cDNA clones encoding Wus were isolated from the cDNA prepared from cambium of Populus tomentosa by the gene specific RT-PCR amplification. The two cDNAs were 922 bp and 956 bp in length with corresponding open reading frames (ORFs) which are capable of encoding the protein of 258 and 264 amino acids (aa), respectively. The deduced aa sequence of them shared 76.0% and 74.9% identity with functional domain of A.thaliana Wus, respectively. They were, therefore, named as PtWus-1 and PtWus-2. The genomic sequences of PtWus-1 and PtWus-2 in 36 individuals were aligned, compared and analyzed using the software MEGA3.1 and DnaSP4.0. A total of 58 and 51 single nucleotide polymorphisms (SNPs) were detected and the diversity of them was 1/27 bp and 1/30 bp, respectively. As for PtWus-1, 24 of 58 were common SNPs and 34 were rare SNPs. There were 43 transitions and 15 transversions of mutation types. In total, 21 SNPs were detected in the coding regions of PtWus-1, of which 16 were silent mutations and 4 were missense mutations and 1 was nonsense mutation. In PtWus-2, 28 were common SNPs and 23 were rare SNPs, of which 36 were transitions and 15 transversions of mutation types. In total, 26 SNPs were detected in coding regions of PtWus-2, in which the numbers of silent mutations and missense mutations were 13. The linkage disequilibrium of SNPs in the PtWus-1 and PtWus-2 was detected and the result showed that LD declined rapidly within the gene regions of PtWus-1 and PtWus-2. It suggested 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 foundation for association genetics of Wus genes and gene assisted breeding of new germplasms with desirable wood fiber traits in P. tomentosa.

Key words: Key words: Populus tomentosa, plant stem cells, Wuschel gene, single nucleotide polymorphisms