Agriculture Reference
In-Depth Information
chitinase and the antibiotic chromobactomycin can act synergistically to suppress
plant disease by
Chromobacterium
sp. strain C61.
ACC Deaminase
Plant growth can also be stimulated by PGPR including PS bacteria that produce
1-aminocyclopropane-1-carboxylate (ACC) deaminase, which cleaves ACC, the
immediate precursor of the plant hormone ethylene, to produce
α
-ketobutyrate and
ammonia (Todorovic and Glick
2008
; Ahmad et al.
2013
). Ethylene is an important
signaling molecule in plants which under pathogen attack or abiotic stress results in
plant growth inhibition (Abeles et al.
1992
). Following infection by a pathogen, a
strong correlation between the timing of ethylene production increase and the
development of chlorotic, necrotic, or wilt symptoms is reported (Goto
et al.
1980
; Elad
1988
; Boller
1991
). Inoculation of plants with ACC deaminase
positive PGPR reduced the stress levels of ethylene and resulted in longer roots and
promoted plant growth following environmental- or pathogen-induced stress (Glick
et al.
1998
,
2007
; Farwell et al.
2007
). For example, ACC deaminase-producing
biocontrol bacteria were more effective in preventing growth inhibition on cucum-
ber plants caused by root pathogen
P. ultimum
and in potato plants by root rot
pathogen
Erwinia carotovora
(Wang et al.
2004
). In a recent example, the ACC
deaminase-producing
Methylobacterium
inoculated with tomato showed signifi-
cantly reduced disease symptoms caused by
Ralstonia solanacearum
and lowered
ethylene emission under greenhouse condition. The ACC and ACO
(1-aminocyclopropane-1-carboxylate oxidase) accumulation in tomato leaves was
significantly reduced with
Methylobacterium
strain inoculation. While ACC oxi-
dase gene expression was found higher in plants treated with
R. solanacearum
than
Methylobacterium
sp. treatment, PR proteins related to ISR like
-1,3-glucanase,
PAL, PO, and PPO were increased in
Methylobacterium
sp. inoculated plants. A
significant increase in
β
β
-1,3-glucanase and PAL gene expression was found in all
the
Methylobacterium
spp. treatments compared to the
R. solanacearum
treatment
(Yim et al.
2013
). In addition, transgenic tomato plants expressing a bacterial ACC
deaminase gene under the transcriptional control of a root-specific promoter, which
mimics the effect of adding ACC deaminase-producing plant growth-promoting
bacteria to the plant roots, have been reported to significantly protect against
damages from
Verticillium
wilt compared to non-transformed tomato plants
(Robison et al.
2001
). Stearns et al. (
2012
) also observed the ACC deaminase
activity in PS bacterium
P. putida
and used it to evaluate its effect on growth
promotion of
Brassica napus
(canola). Transcriptional changes in bacterially
treated canola plants were investigated employing an
A. thaliana
oligonucleotide
microarray. The results indicated that the transcription of genes involved in plant
hormone regulation, secondary metabolism, and stress response was altered in
inoculated plants, whereas the upregulation of genes for auxin response factors
and the downregulation of stress response genes were observed only in the presence
of bacterial ACC deaminase. These results, therefore, support the hypothesis that
