| Poplus simonii×P.nigra spread widly in Northeast of China, which grow quickly and have good wood quanlity, is used in the pulp and paper industry. To clone and identify the genes involved in wood formation in Populus simonii×P.nigra, We adopt imitate gravity stress the cambial tissue of Populus simonii×P.nigra, this paper did some researches as follows.We constructed two cDNA libraries from the cambial tissue of Populus simonii×P. nig ra after imitate gravity stress and the recombination rate of constructed library are 98% and 95% PCR detection revealed that the average inserts size were respectively 1.2kb and 1.3kb in length.A total of 6 048 expressed sequence tags (ESTs) were generated through randomly picked sequencing process, with the GenBank accession numbers of GH626174-GH 632222. The total of 6 048 ESTs represented 5 007 non-redundant unique transcripts, including 621 contigs and 4 386 singletons. In total,5 334 ESTs showed significant similarity to the sequences in Nr database of NCBI, and they were further classfied into 12 functional categories based on their putative functions, i.e. Function unknown (30.56%), Metabolism (13.3%), protein synthesis (11.25%), Signal transduction (8.49%), Protein destination (6.45%), Transport facilitation (6.03%), Cell rescue, defense (5.85%), Transcription (5.8%), Cell structure (4.45%),Cell growth, division (3.46%), Energy (3.5%) and Photosynthesis(0.86%). In total,437genes genes potentially involved in lignin biosynthesis, cell wall structure, synthesis of cell wall polysaccharides or development regulation were identified. These genes, which accounted for 7.2% of the total ESTs, may be involved in cambium development.To investigate the expression of genes involved in lignin biosynthesis, cell wall formation, or cell growth-related genes during the growth periods of Populus simonii×P.nigra after gravity stress, RT-PCR analyses were conducted. Eleven genes were selected for expression analysis. The results showed these gene expression patterns are significant difference.The genes which involve in cellulose biosynthesis such as CesA, SUSY, ACO, the expression patterns of these genes were higher in TW than in OW. Especially,the gene expression trends of FLAs.However,some genes involve in lignin biosynthesis, for example, CCoAOMT, PAL, laccase and POD, the expression patterns of these genes were lower in in TW than in OW. The expression of transcription factor MYB in TW was more than in OW.Total of 13 full-length genes were cloned from Populus simonii×P.nigra, including 4-coumarate:CoA ligase, peroxidases and laccase.In conclusion, our study domnstrated the gene expression in the cambial tissue of Populus simonii×P.nigra after gravity stress, and 50genes invovled in wood formation were identified. Furthermore, the time course expression of 11 genes during wood formation were analyzed.This study will make a foundation for cultivating better new Poplus simonii×P.nigra species of pulp timber by decreasing the content of lignin in tree species or changing its components, meanwhile,it enriched our knowledge of wood development on a molecular level, and may be useful in the application of genetic tools for improving the quality of commercial supplies to the benefit of wood, and wood-product, users.
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