Obembe, Olawole O.
Promiscuous, non-catalytic, tandem carbohydrate-binding
modules modulate the cell-wall structure and development
of transgenic tobacco (Nicotiana tabacum) plants.
Journal of Plant Research , 120.
We have compared heterologous expression of
two types of carbohydrate binding module (CBM) in tobacco
cell walls. These are the promiscuous CBM29
modules (a tandem CBM29-1-2 and its single derivative
CBM29-2), derived from a non-catalytic protein1, NCP1,
of the Piromyces equi cellulase/hemicellulase complex,
and the less promiscuous tandem CBM2b-1-2 from the
Cellulomonas fimi xylanase 11A. CBM-labelling studies
revealed that CBM29-1-2 binds indiscriminately to every
tissue of the wild-type tobacco stem whereas binding of
CBM2b-1-2 was restricted to vascular tissue. The promiscuous
CBM29-1-2 had much more pronounced effects on
transgenic tobacco plants than the less promiscuous
CBM2b-1-2. Reduced stem elongation and prolonged
juvenility, resulting in delayed flower development, were
observed in transformants expressing CBM29-1-2 whereas
such growth phenotypes were not observed for CBM2b-1-2
plants. Histological examination and electron microscopy
revealed layers of collapsed cortical cells in the stems of
CBM29-1-2 plants whereas cellular deformation in the
stem cortical cells of CBM2b-1-2 transformants was less
severe. Altered cell expansion was also observed in most
parts of the CBM29-1-2 stem whereas for the CBM2b-1-2
stem this was observed in the xylem cells only. The cellulose
content of the transgenic plants was not altered.
These results support the hypothesis that CBMs can modify
cell wall structure leading to modulation of wall loosening
and plant growth.
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