Functional characterisation of Nicotiana tabacum xyloglucan endotransglycosylase (NtXET-1): generation of transgenic tobacco plants and changes in cell wall xyloglucan |
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Authors: | Karin Herbers Ester P Lorences Coral Barrachina Uwe Sonnewald |
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Institution: | (1) U.D. Fisiología Vegetal, Facultad de Ciencias Biológicas, Univ. de Valencia, Dr. Moliner 50, Burjassot, 46100 Valencia, Spain, ES;(2) Institut für Pflanzengenetik und Kulturpflanzenforschung, Corrensstr. 3, 06466 Gatersleben, Germany, DE |
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Abstract: | 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.
Received: 24 January 2000 / Accepted: 21 July 2000 |
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Keywords: | : Cell wall Nicotiana (cell wall) Transgenic tobacco Xyloglucan Xyloglucan endotransglycosylase |
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