Identification of Developing Xylem-Specific Promoters from Poplar by Using tissue type-Specific Whole Genome Transcriptome Analysis.

Lignocellulosic feedstock (i.e., wood) is gaining popularity as a source of fermentable sugars for liquid fuel production. To improve the quantity and quality of woody biomass, the developing xylem (DX) cell-specific genetic modification is desired. Bioinformatic analyses followed by the validation of cell type-specific transcriptomes led to the identification of 37 transcripts specifically expressed in DX. After further confirmation of DX-specific expression, we selected four genes (DX5, DX8, DX11 and DX15) to demonstrate the feasibility of our strategy. The promoter regions of selected DX genes were isolated and produced stable transformants of poplar by using transcriptional promoter:-glucuronidase (GUS) fusion constructs. The GUS expression patterns of DX5 and ANAC073 (orthologous gene of Arabidopsis) revealed that these promoters were active in xylem cells in poplar at early seedling growth, and showed strongest expression in the developing xylem cells in the wood formation/development at later growth stages of poplar. DX specific and strong expression patterns of all the other DX promoters (DX8, DX11 and DX15) tested suggests that these promoters may be useful to control transgene expression in the DX cells of woody plants with the aim of the feedstock improvement.

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