INHIBITION OF TOBACCO NADH-HYDROXYPYRUVATE REDUCTASE BY EXPRESSION OFA HETEROLOGOUS ANTISENSE RNA DERIVED FROM A CUCUMBER CDNA - IMPLICATIONS FOR THE MECHANISM OF ACTION OF ANTISENSE RNAS
Mj. Oliver et al., INHIBITION OF TOBACCO NADH-HYDROXYPYRUVATE REDUCTASE BY EXPRESSION OFA HETEROLOGOUS ANTISENSE RNA DERIVED FROM A CUCUMBER CDNA - IMPLICATIONS FOR THE MECHANISM OF ACTION OF ANTISENSE RNAS, MGG. Molecular & general genetics, 239(3), 1993, pp. 425-434
Tobacco plants were genetically transformed to generate antisense RNA
from a gene construct comprised of a full-length cucumber NADH-depende
nt hydroxypyruvate reductase (HPR) cDNA placed in reverse orientation
between the cauliflower mosaic virus 35S promoter and a nopaline synth
ase termination/polyadenylation signal sequence. In vivo accumulation
of antisense HPR RNA within eight independent transgenic tobacco plant
s resulted in reductions of up to 50% in both native HPR activity and
protein accumulation relative to untransformed tobacco plants (mean tr
ansgenote HPR activity = 67% wild type, mean transgenote HPR protein =
63% wild type). However, in contrast to previous reports describing a
ntisense RNA effects in plants, production of the heterologous HPR ant
isense RNA did not systematically reduce levels of native tobacco HPR
mRNA (mean transgenote HPR mRNA level = 135% wild type). Simple regres
sion comparison of the steady-state levels of tobacco HPR mRNA to thos
e of HPR antisense RNA showed a weak positive correlation (r value of
0. 548, n = 9; n is wild type control plus eight independent transform
ants; significant at 85% confidence level), supporting the conclusion
that native mRNA levels were not reduced within antisense plants. Alth
ough all transgenic antisense plants examined displayed an apparent re
duction in both tobacco HPR protein and enzyme activity, there is no c
lear correlation between HPR activity and the amount of either sense (
r = 0.267, n = 9) or antisense RNA (r = 0. 1 75, n = 9). This compares
to a weak positive correlation between HPR mRNA levels and the amount
of HPR activity observed in wild-type SR1 tobacco plants (r = 0.603,
n = 5). The results suggest that in vivo production of this heterologo
us HPR antisense RNA is inhibitory at the level of HPR-specific transl
ation and produces its effect in a manner not dependent upon, nor resu
lting in, a reduction in steady-state native HPR mRNA levels. In this
context, the observed antisense effect appears to differ mechanistical
ly from most antisense systems described to date.