Identification and functional characterization of the promoter driving “xyloglucan endotransglucosylase/hydrolase gene (XET)” gene for root growth in the desert Populus euphratica

Xyloglucan endotransglucosylase/hydrolase family genes encode enzymatic proteins that potentially have two different catalytic activities either endotransglucosylase (XET) or endohydrolase (XEH) activity. Endotransglucosylase catalyze the breakdown and molecular grafting of the β-(1-4)-xyloglucan backbone and endohydrolase catalyze the irreversible shortening. We are interested in understanding the molecular mechanism of the upstream region of the XET gene. An expression unit consisting of the b-glucuronidase (gusA) reporter gene under the control of 1831 bp fragment of the Populus euphratica XET (PeXET) promoter was introduced into tobacco via Agrobacterium tumefaciens. The sequence was identified as PeXET promoter as it contain all the upstream sequences required for a typical promoter. Analysis of the promoter sequence indicated some basic cis-acting elements were related to various environmental stresses, developmental response and plant hormones responses. Functional properties of the promoter were examined by GUS staining and fluorescence quantitative analyses using at least three PCR-positive transgenic tobacco plants, treated with various plant hormones iso-osmotic and environmental stresses for different times. We demonstrated that the PeXET promoter was a multistress-inducible promoter. To explain the unknown features of the upstream regulatory mechanism of the PeXET gene in desert plants, we suggest that the function of the PeXET promoter, especially under environmental stress conditions, to be studied for possible value in molecular breeding as new promoters of stress-resistance genes for desert plants.