27 research outputs found
Spermine facilitates recovery from drought but does not confer drought tolerance in transgenic rice plants expressing Datura stramonium S-adenosylmethionine decarboxylase
Polyamines are known to play important roles
in plant stress tolerance but it has been difficult to determine
precise functions for each type of polyamine and their
interrelationships. To dissect the roles of putrescine from
the higher polyamines spermidine and spermine, we generated
transgenic rice plants constitutively expressing a
heterologous S-adenosylmethionine decarboxylase (SAMDC)
gene from Datura stramonium so that spermidine and
spermine levels could be investigated while maintaining a
constant putrescine pool. Whereas transgenic plants
expressing arginine decarboxylase (ADC) produced higher
levels of putrescine, spermidine and spermine, and were
protected from drought stress, transgenic plants expressing
SAMDC produced normal levels of putrescine and showed
drought symptoms typical of wild type plants under stress,
but the transgenic plants showed a much more robust
recovery on return to normal conditions (90% full recovery
compared to 25% partial recovery for wild type plants). At
the molecular level, both wild type and transgenic plants
showed transient reductions in the levels of endogenous
ADC1 and SAMDC mRNA, but only wild type plants
showed a spike in putrescine levels under stress. In transgenic
plants, there was no spike in putrescine but a smooth
increase in spermine levels at the expense of spermidine.
These results confirm and extend the threshold model for
polyamine activity in drought stress, and attribute individual
roles to putrescine, spermidine and spermine
Development of a novel gene transfer system for Cajanus cajan and expression of a monocot arginine decarboxylase cDNA in transformed cell lines
We describe the development of a novel transformation system for pigeonpea (Cajanus cajan (L.) Millsp.) cell lines
using particle bombardment. The aim of our study was not only to develop a transformation system for this important but
recalcitrant species but to do so using a gene of interest and to study the behaviour of this transgene in a legume background.
The gene we chose for our studies was the heterologous oat arginine decarboxylase cDNA. Transgenic lines engineered with
this cDNA had a small, but significant increase in arginine decarboxylase activity (ADC; EC 4.1.1.17). We detected an increase
in putrescine levels in all the lines we analysed irrespective of whether major or minor changes in ADC activity were observed.
Spermidine and spermine levels were also increased in some of the lines. We confirmed that small changes in the adc message
(mRNA) had a significant effect on enzyme activity and more importantly on polyamine levels. This is the first report describing
modulation of a gene involved in a metabolic pathway in transgenic pigeonpea tissues
Molecular characterization of the Arginine decarboxylase gene family in rice
Arginine decarboxylase (ADC) is a key
enzyme in plants that converts arginine into putrescine,
an important mediator of abiotic stress tolerance.
Adc genes have been isolated from a number of
dicotyledonous plants but the oat and rice Adc genes
are the only representatives of monocotyledonous
species described thus far. Rice has a small family of
Adc genes, and OsAdc1 expression has been shown to
fluctuate under drought and chilling stress. We
identified and characterized a second rice Adc gene
(OsAdc2) which encodes a 629-amino-acid protein
with a predicted molecular mass of 67 kDa. An
unusual feature of the OsAdc2 gene is the presence
of an intron and a short upstream open reading frame
in the 50-UTR. Sequence comparisons showed that
OsAdc2 is more closely related to the oat Adc gene
than to OsAdc1 or to its dicot homologs, and mRNA
analysis showed that the two rice genes are also
differently regulated. Whereas OsAdc1 is expressed in
leaf, root and stem, OsAdc2 expression is restricted to
stem tissue. Protein expression was investigated with
specific antibodies against ADC1 and ADC2, corroborating
the mRNA data. We discuss the expression
profiles of OsAdc1 and OsAdc2 and potential functions
for the two corresponding proteins
Transgenic wheat plants expressing an oat arginine decarboxylase cDNA exhibit increases in polyamine content in vegetative tissue and seeds
We generated and characterized a trans-
genic wheat (
Triticum aestivum
L.) population
expressing constitutively an oat
arginine decarboxylase
(
ADC
) cDNA. Transgenic wheat plants expressing the
transgene had a significant increase in ADC activity
with no concomitant changes in ODC activity. We
measured 2-fold increases in putrescine, spermidine and
spermine content in leaves of transgenic plants com-
pared to wild-type. These plants also exhibited
significant increases in the three polyamines in seeds
(7-fold putrescine, 2.5-fold spermidine and 1.8-fold
spermine). This significant polyamine accumulation
was heritable in subsequent generations. In order to
characterize molecularly this population we cloned a
partial
TaADC
cDNA. This sequence was used as a
probe to ascertain the presence of two distinct ADC
transcripts in wheat. Further DNA analyses confirmed
the presence of at least two distinct
ADC
genes in the
wheat genome. Our results demonstrate that polyamine
levels can be altered in transgenic wheat plants resulting
in phenotypically normal and fertile plants. This
transgenic wheat population will serve as useful germ-
plasm to embark on further in depth studies to ascertain
the role of polyamines in abiotic stress responses