Overexpression of gene GA20ox encoding gibberellin 20-oxidase (GA20-oxidase)
in plants has resulted in improved stem elongation and growth rate. However,
constitutive overexpression of GA20ox driven by the cauliflower mosaic virus
(CaMV) 35S promoter is frequently accompanied by undesirable phenotypes such
as poor rooting and small leaves.
A study conducted by a team of Vietnamese researchers has determined whether
the expression of GA20-oxidase in tobacco (Nicotiana tabacum) would increase
stem elongation and enhance xylem formation. The binary vector pBI101
carrying GA20 gene encoding GA20-oxidase (binding c-myc tail) under the
control of xylem-specific promoter CAD4 was successfully constructed and
transformed into Agrobacterium tumefaciens strain C58.
All the transgenic lines showed the xylem-specific expression of
GA20-oxidase when using RT-PCR reaction. All 5 selected transgenic tobacco
lines exhibited enhanced stem elongation compared to wild type (WT) control
lines, the stem heights of transgenic lines increased from 20 to 60% than WT
lines. The stem elongation rates of transgenic lines are significantly
higher compared to WT. The histological staining of stem cross section
showed that all the selected transgenic lines exhibited a substantial
increase in xylem differentiation compared to WT, xylem widths of transgenic
lines increased from 17-59% than WT. These results confirmed that GA20
affected xylem differentiation and enhanced wood formation.