Agriculture Reference
In-Depth Information
infectedplantcells.Thismakesthemparticularlyusefulforinsertionofgenesof
interest.
As yet no commercial cultivars have been produced by transformation of
apples or pears but transformed plants of interest have been produced along
a number of different lines.
Rol
gene transfer
Agrobacterium rhizogenes
carries genes that alter the growth of infected plant cells.
Some of the genes on the T-DNA within the
A
rhizogenes
R
i
-plasmid control
auxin and cytokinin levels, others alter sensitivity to these hormones (Schell
et al.
,
.
). A group of these genes are known as the
rol
(root
inducing locus) genes. A number of plant species regenerated from 'hairy
root' cells following
A. rhizogenes
infection show shortened stem internodes,
increased branching and reduced apical dominance. Plants transformed with
single
rol
genes or combinations of these also exhibit altered growth character-
istics. Transformed plants overexpressing the
rol
A gene show reduced growth
and increased root development. Plants transformed with the
rol
B gene show
reduced apical dominance, increased rooting and reduced leaf senescence,
possibly because the
rol
B gene product alters auxin sensitivity. Plants over-
expressing the
rol
C gene are more dwarfed, with reduced apical dominance,
increased branching and increased root growth. The effects are most pro-
nounced when plants are transformed with several
rol
genes in combination
(Holefors,
; Tamas,
). Some of the induced characteristics are potentially important
with regard to tree size control for high-density orchards.
The problem of vigour control is particulary acute for pears when grown in
conditions unsuitable for dwarfing quince rootstocks. Bell
et al
.(
) estab-
lished shoot proliferation cultures of 'Beurre Bosc' pear and transformed leaf
explantsfromtheseusingthedisarmed
A. tumefaciens
strainEHAIOIcontaining
pGA-GUSGF
rol
C, the
rol
C gene (ORF-
in
A. rhizogenes
) being controlled by
itsnativepromoter.Theinoculationoffreshlyharvestedleaveswasachievedby
cutting them with sterile scalpel blades dipped in the bacterial suspension and
the leaves co-cultivated prior to transfer to antibiotic selection plates (contain-
ing SIM, kanomycin and timentin), followed by growth on a shoot expression
medium and subsequent shoot proliferation culture.
Transformation with the
rol
C gene was confirmed by DNA, RNA and pro-
tein blot analysis. The transformed pears, grown on in a greenhouse after bud-
ding on 'Bartlett' seedling rootstock, had fewer nodes, much shorter internodes
and at
weeks were only about
% of the height of the controls. Holefors
et al.
(
) produced transformed clones of the apple rootstock 'M.
' by in-
fection of
in-vitro
-produced leaves with
A. tumefaciens
strain GV
containing
a binary vector carrying the
npt
II gene and the
rol
A gene on the T-DNA. All
