Functional characterisation of Nicotiana tabacum xyloglucan endotransglycosylase (NtXET-1): generation of transgenic tobacco plants and changes in cell wall xyloglucan.
To study the function of xyloglucan endotransglycosylase (XET) in vivo we isolated, a tomato (Lycopersicon esculentum Mill.) XET cDNA (GenBank AA824986) from the homologous tobacco (Nicotiana tabacum L.) clone named NtXET-1 (Accession no. D86730). The expression pattern revealed highest levels of NtXET-1 mRNA in organs highly enriched in vascular tissue. The levels of NtXET-1 mRNA decreased in midribs with increasing age of leaves. Increasing leaf age was correlated with an increase in the average molecular weight (MW) of xyloglucan (XG) and a decrease in the relative growth rates of leaves. Transgenic tobacco plants with reduced levels of XET activity were created to further study the biochemical consequences of reduced levels of NtXET-1 expression. In two independent lines, total XET activity could be reduced by 56% and 37%, respectively, in midribs of tobacco plants transformed with an antisense construct. The decreased activity led to an increase in the average MW of XG by at least 20%. These two lines of evidence argue for NtXET-1 being involved in the incorporation of small XG molecules into the cell wall by transglycosylation. Reducing the incorporation of small XG molecules will result in a shift towards a higher average MW. The observed reduction in NtXET-1 expression and increase in the MW of XG in older leaves might be associated with strengthening of cell walls by reduced turnover and hydrolysis of XG.
Herbers
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U.D. Fisiología Vegetal, Facultad de Ciencias Biológicas, Univ. de Valencia, Spain.
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Barrachina
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Sonnewald
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D002473:Cell Wall / Q000378:metabolism*; D018076:DNA, Complementary; D005936:Glucans; D016695:Glycosyltransferases / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D030821:Plants, Genetically Modified / Q000378:metabolism; D010947:Plants, Toxic; D011134:Polysaccharides / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D014026:Nicotiana / Q000201:enzymology*; D014990:Xylans
D018076:DNA, Complementary; D005936:Glucans; D011134:Polysaccharides; D012333:RNA, Messenger; D014990:Xylans; C029353:xyloglucan; D016695:Glycosyltransferases; C073693:xyloglucan endotransglycosylase