REVIEW

Recent developments in use of 1-aminocyclopropane-1-carboxylate (ACC) deaminase for conferring toleranceto biotic and abiotic stress

Iti Gontia-Mishra • Shaly Sasidharan •

Sharad Tiwari

Received: 7 November 2013 / Accepted: 7 January 2014

� Springer Science+Business Media Dordrecht 2014

Abstract Ethylene is an essential plant hormone

also known as a stress hormone because its synthesis is

accelerated by induction of a variety of biotic and

abiotic stress. The plant growth promoting bacteria

containing the enzyme 1-aminocyclopropane-1-car-

boxylate (ACC) deaminase enhances plant growth by

decreasing plant ethylene levels under stress condi-

tions. The expression of ACC deaminase (acdS) gene

in transgenic plants is an alternative approach to

overcome the ethylene-induced stress. Several trans-

genic plants have been engineered to express both

bacterial/plant acdS genes which then lowers the

stress-induced ethylene levels, thus efficiently com-

bating the deleterious effects of environmental

stresses. This review summarizes the current knowl-

edge of various transgenic plants overexpressing

microbial and plant acdS genes and their potential

under diverse biotic and abiotic stresses. Transcription

regulation mechanism of acdS gene from different

bacteria, with special emphasis to nitrogen fixing

bacteria is also discussed in this review.

Keywords 1-Aminocyclopropane-1-

carboxylic acid (ACC) � ACC deaminase gene �Ethylene-induced stress �Microbial acdS genes �Plant acdS genes � Plant-growth promoting

rhizobacteria (PGPR) � Transgenic plants

Introduction

Plants, being sessile, are exposed to a range of

environmental stresses and have to adapt themselves

accordingly. Environmental stresses are of two kinds:

biotic and abiotic. Abiotic stresses include drought,

flooding, salinity, heat, cold, wounding as well as

exposure to xenobiotic, heavy metals and ultra-violet

radiation. Furthermore, plants are also exposed to

biotic stresses including microbial pathogens such as

bacteria, fungi and nematodes. These stresses, either in

combination or alone, can adversely affect plant

growth and productivity. The sensing of biotic and

abiotic stresses induce signaling cascades that acti-

vates various ion channels, production of reactive

oxygen species and accumulation of hormones such as

salicylic acid, ethylene, jasmonic acid and abscissic

acid (Fraire-Velazquez et al. 2011).

Ethylene is an essential plant hormone produced by

all plants and mediates a wide range of responses and

developmental processes. It is also a stress hormone

since its synthesis is accelerated by induction of a

variety of stress signals, such as mechanical

I. Gontia-Mishra (&) � S. Sasidharan � S. Tiwari

Biotechnology Centre, Jawaharlal Nehru Agricultural

University, Jabalpur 482004, India

e-mail: itigontia@gmail.com

123

Biotechnol Lett

DOI 10.1007/s10529-014-1458-9

wounding, salinity, drought, water logging, extreme

temperatures, pathogenic infection and pollutants

(Saleem et al. 2007). However, excessive ethylene

produced in germinating seeds or by different envi-

ronmental stresses can hinder plant growth especially

root growth retardation. The synthesis of ethylene in

plants is directly proportionate to the concentration of

its precursor 1-aminocyclopropane-1-carboxylic acid

(ACC) (Shaharoona et al. 2006). Many plant growth-

promoting bacteria produce ACC deaminase and these

bacteria can decrease the level of ethylene produced in

stressed plants by cleaving ACC to a-ketobutyrate and

ammonium ion (Glick 2005; Hontzeas et al. 2004).

The treatment of seeds or seedling roots with ACC

deaminase-containing bacteria reduces the extent of

ethylene inhibition of root length (Penrose et al. 2001).

Plant growth-promoting rhizobacteria (PGPR) con-

taining ACC deaminase are being extensively utilized

for promoting plant growth both under stressful and

normal conditions. Moreover, their use also protects

plants from the deleterious effects of stress ethylene,

which is synthesized due to various environmental

stresses including heavy metals (Burd et al. 2000;

Zhang et al. 2011), flooding and water logging

(Grichko and Glick 2001; Barnawal et al. 2012),

phytopathogens (Wang et al. 2000; Toklikishvili et al.

2010), drought (Mayak et al. 2004; Belimov et al.

2009) and high salt (Saravanakumar and Samiyappan

2007; Jalili et al. 2009; Siddikee et al. 2011).

A large number of transgenic plants have been

genetically engineered to express a bacterial acdS

gene which lowers the ethylene levels in plants and

provides protection against various stresses (Lund

et al. 1998; Grichko et al. 2000; Grichko and Glick

2001; Robison et al. 2001; Nie et al. 2002; Sergeeva

et al. 2006; Farwell et al. 2007; Zhang et al. 2008). By

using transgenic techniques, this enzyme is being

expressed at a high level in plants, providing effective

stress tolerance. This review summarizes the current

knowledge of various transgenic plants overexpress-

ing microbial and plant acdS gene and their potential

under diverse biotic and abiotic stresses.

Source organisms for acdS gene

Both prokaryotes and eukaryotes possess ACC deam-

inase activity. ACC deaminase activity is found in a

wide range of Gram-negative bacteria: Enterobacter

cloacae, Achromobacter xylosoxidans, Rhizobium

leguminosarum, Pseudomonas putida, Burkholderia

phytofirmins, Variovorax paradoxus, Methylobacteri-

um fujisawaense, Cronobacter sakazakii, Mesorhizo-

bium sp. Haererehalobacter sp., Halomonas sp.

(Holguin and Glick 2001; Belimov et al. 2001; Ma

et al. 2003; Hontzeas et al. 2004; Sessitsch et al. 2005;

Madhaiyan et al. 2006; Belimov et al. 2009; Jha et al.

2012). Gram-positive bacteria also contains ACC

deaminase activity: Rhodococcus sp., Brevibacterium

iodinum, Bacillus licheniformis, Zhihengliuela alba,

Micrococcus sp. Brachybacterium saurashtrense,

Brevibacterium casei (Belimov et al. 2001; Dastager

et al. 2010; Siddikee et al. 2011; Gontia et al. 2011; Jha

et al. 2012). Similarly, ACC deaminase is found in

archeabacteria, e.g. Pyrococcus horikoshii (Fujino

et al. 2004). ACC deaminase has also been found in

yeast, e.g. Hansenula saturnus (Minami et al. 1998)

and Issatchenkia occidentalis (Palmer et al. 2007), and

in fungi, e.g. Penicillium citrinum, Trichoderma

asperellum, Phytophthora sojae (Jia et al. 1999;

Viterbo et al. 2010; Singh and Kashyap 2012).

Recently, ACC deaminase activity has also been

reported in plants e.g. Arabidopsis thaliana, Populus

tremula and tomato (McDonnell et al. 2009; Plett et al.

2009). Moreover, as known from the available liter-

ature, acdS genes from bacteria are being extensively

used for the development of transgenic plants.

Expression of acdS gene in plants

Transgenic plants overexpressing the acdS gene from

bacteria have been developed and studied for their

tolerance towards different abiotic and biotic stresses.

The details of the source of acdS genes, promoters and

vectors used for the development of transgenic crops

overexpressing ACC deaminase enzyme have been

provided in Table 1.

Salinity

Salinity is one of the important abiotic stresses that

limit the crop growth and its productivity. In addition,

salinity also affects nutrient uptake by plants. There

are many reports that show treatment of plants with

PGPR having ACC deaminase activity reduces the

level of stress ethylene and confers salinity tolerance

in plants grown under high salt concentrations (Cheng

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123

et al. (2007); Saravanakumar and Samiyappan (2007);

Jalili et al. (2009); Siddikee et al. (2011). Transgenic

canola (Brassica napus) expressing acdS gene from

Pseudomonas putida strain UW4 was developed and

evaluated for their ability to withstand saline condi-

tions (Sergeeva et al. 2006). The bacterial acdS gene

was placed separately under the transcriptional control

of strong 35S promoter from cauliflower mosaic virus

(CaMV), the root-specific rolD promoter from the Ri

plasmid of Agrobacterium rhizogenes and a patho-

genesis-related prb-1b promoter from tobacco. Trans-

genic canola plants expressing acdS gene under the

control of rolD gave better results for tolerance to salt

in the presence of 0–200 mM NaCl than 35S CaMV

and prb-1b transformants. Transgenic plants express-

ing a bacterial acdS gene and treatment of plants with

ACC deaminase-containing PGPR can be used as

alternative approaches for facilitating better plant

growth in saline environments.

Flooding or water logging

Flooding is a common abiotic stress that adversely

affects growth of many plants as roots are inflicted

with anoxia (lack of O2) triggering epinasty, leaf

chlorosis, necrosis and consequently yield reduction.

Ethylene is produced in large quantities in shoots

during flooding stress because of increased activity of

Table 1 Expression of ACC deaminase gene in different transgenic plants

Transgenic

plant

ACC deaminase

gene from bacteria/

plant

Stress tolerance Promoter Vector Reference

Tomato Pseudomonas

chloraphis 6G5

Ethylene 35S CaMV pMON893 Klee et al. (1991)

Tomato Pseudomonas

chloraphis 6G5

Ethylene 35S CaMV pMON893 Reed et al. (1995)

Tomato Pseudomonas

chloraphis 6G5

Xanthomonas campestris,

Pseudomonas syringae and

Fusarium oxysporum

35S CaMV pMON893 Lund et al. (1998)

Tomato Enterobacter

cloacae UW4

Cd, Co, Cu, Ni, Pb, Zn 35S CaMV or

pRB-1b or

rolD

– Grichko et al. (2000)

Tomato Enterobacter

cloacae UW4

Verticillium wilt (fungal pathogen), 35S CaMV or

pRB-1b or

rolD

pKYLX7 Robison et al.

(2001); Tamot

et al. (2003)

Tomato Enterobacter

cloacae UW4

UV-B light 35S CaMV or

pRB-1b or

rolD

pKYLX7 Tamot et al. (2003)

Tomato Enterobacter

cloacae UW4

Flood 35S CaMV or

pRB-1b or

rolD

– Grichko and Glick

(2001)

Canola Enterobacter

cloacae CAL 2

As 35S CaMV

promoter

pKYLX7 Nie et al. (2002)

Canola Pseudomonas putida

UW4

Ni rolD pKYLX7 Stearns et al. (2005)

Canola Pseudomonas putida

UW4

Salt (0–200 mM) 35S CaMV or

pRB-1b or

rolD

pKYLX7 Sergeeva et al.

(2006)

Canola Pseudomonas putida

UW4

Ni and Flood Root specific

rolD promoter

pKYLX7 Farwell et al. (2007)

Petunia/

Tobacco

Pseudomonas putida Co, Cu 35S CaMV pBI101 Zhang et al. (2008)

Arabidopsis

thaliana

Arabidopsis

thaliana

– 35S CaMV pCAMBIA

1305

McDonnell et al.

(2009)

Biotechnol Lett

123

ACC synthase in the submerged roots. Treatment of

plants with PGPR having ACC deaminase activity to

alleviate waterlogging stress have been reported by

few researchers (Grichko and Glick 2001; Barnawal

et al. 2012). Transgenic tomato (Lycopersicon escu-

lentum) plants expressing the acdS gene from Enter-

obacter cloacae UW4 were separately placed under

the transcriptional control of 35S CaMV, rolD

promoter and prb-1b promoter have been studied for

their response due to flooding stress (Grichko and

Glick 2001). Transgenic tomato plants with acdS gene

under the control of different promoter displayed

increased tolerance towards flooding. However, trans-

genic plants with acdS gene driven by the rolD

promoter performed better as compared to other

transformants under flooding conditions.

Similarly, transgenic canola plants were developed

expressing acdS gene from Pseudomonas putida UW4

under the control of the root specific rolD promoter from

Agrobacterium rhizogenes to evaluate their response for

flooding stress (Farwell et al. 2007). These transgenic

plants and canola plants were treated with P. putida

UW4 and these plants performed better (in terms of

shoot length and shoot biomass) as compared to the non

transformed plants under low-flood stress conditions.

Using either transgenic canola or treatment of plants

with P. putida UW4 provided similar enhanced and

additive tolerance under low flood-stress conditions.

Thus, use of acdS gene expressing transgenic plants and

PGPR having ACC deaminase activity are effective

strategies for amelioration of damage to plants caused

by flooding stress conditions.

Transition and heavy metals

Higher concentrations of essential or non-essential

metal ions of Zn, As, Cd, Co, Pb, Ni, and Cu are

deleterious to metal-sensitive enzymes, thus hindering

the plant growth. Some ACC deaminase-producing

PGPR promote plant growth by lowering the level of

ethylene in plants growing in the presence of heavy

metals (Glick 2005; Zhang et al. 2011). A number of

transgenic plants expressing bacterial acdS gene have

been developed for combating heavy metal stress thus

utilizing them for phytoremediation of contaminated

soils. Grichko et al. (2000) developed transgenic

tomato plants expressing acdS gene from Enterobac-

ter cloacae UW4 separately under the control of two

tandem 35S CaMV promoters, the rolD promoter

from Agrobacterium rhizogenes and the pathogenesis-

related prb-1b promoter from tobacco. The growth of

transgenic tomato plants in the presence of cadmium,

copper, cobalt, magnesium, nickel, lead or zinc was

monitored. Transgenic tomato plants expressing acdS

gene particularly controlled by the prb-1b promoter

accumulated larger amounts of metals within the plant

tissues.

Transgenic canola plants (Brassica napus) express-

ing acdS gene from E. cloacae UW4 were developed

and examined for their ability to thrive in the presence

of arsenate in the soil (Nie et al. 2002). Transgenic

canola with a acdS gene accumulated larger amounts of

arsenate from the contaminated soil as compared to

non-transformed plants. This suggests that acdS gene

lowers stress-induced ethylene levels thus making these

plants tolerant to heavy metal stress. In another study,

the acdS gene from Pseudomonas putida UW4 was

introduced into canola driven separately by double

35S CaMV promoter and root specific rolD promoter

from the Agrobacterium rhizogenes (Stearns et al.

2005). These transgenic lines were studied for phyto-

remediation of nickel-contaminated soil. Transgenic

plants driven by rolD promoter exhibited better growth

in soil contaminated with nickel and accumulated more

nickel in shoot tissue in comparison to non-transgenic

and transgenic plants with 35S CaMV promoter. Sim-

ilarly, transgenic canola plants expressing acdS gene

from Pseudomonas putida UW4 under the control of

the root-specific, plant promotor (rolD) from Agrobac-

terium rhizogenes were evaluated for their response

towards nickel stress (Farwell et al. 2007). They have

also examined the effect of treatment of PGPR, P.

putida strainUW4 and P. putida strain HS-2 on

transgenic and non-transgenic plants for phytoremedi-

ation of nickel-contaminated soil in situ. It was

observed ACC deaminase-containing bacteria

enhanced plant growth of both transgenic and non-

transformed canola, resulting in *10 % increase in

total nickel per plant in comparison to untreated plants.

Recently, transgenic petunia and tobacco plants

were developed expressing iaaM gene from Agrobac-

terium encoding a tryptophan monooxygenase (iaaM)

alone or in combination with the acdS gene from P.

putida UW4 impelled by 35S CaMV constitutive

promoter. These transgenic plants were studied for

their response towards copper- and cobalt-contami-

nated soils (Zhang et al. 2008). Plants expressing only

iaaM gene tolerated metal stress better than the non-

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123

transgenic plants. However, transgenic plants co-

expressing both iaaM and acdS genes accumulated

more metal ions into the plant shoots and could

tolerate CuSO4 up to150 mg l-1. Transgenic plants

expressing acdS gene and treatment of plants with

PGPR having ACC deaminase were equally useful in

the promotion of seed germination, root elongation

and heavy metal accumulation under contaminated

soils. These results will stimulate further efforts to

develop plant-based technologies for the removal of

environmental pollutants from contaminated

environments.

Phytopathogens

Ethylene synthesis in plants significantly increases

during infection by pathogens and can also be induced

by treatment with pathogen-derived elicitors (Fran-

kenberger and Arshad 1995). Ethylene acts as a

messenger during plant–microbe interactions and all

types of diseases caused by fungi, bacteria, viruses and

nematodes shows an enhanced ethylene response.

ACC is a precursor for ethylene synthesis; thus

microorganisms with ACC deaminase activity can

lower the ACC levels of host plant, thereby decreasing

ethylene generation. Some of the researchers have

reported that treatment of plants with PGPR having

ACC deaminase activity helps in conferring stress-

ethylene generated by phytopathogens (Wang et al.

2000; Toklikishvili et al. 2010). Transgenic plants

expressing acdS gene have been developed to reduce

the stress-ethylene synthesis induced by pathogens.

Transgenic tomato plants expressing acdS gene from

Pseudomonas chloraphis 6G5, under the transcrip-

tional control of 35S CaMV constitutive promoter,

were studied for responses to infections of Xantho-

monas campestris, Pseudomonas syringae or Fusar-

ium oxysporum (Lund et al. 1998) and all transgenic

plants expressing the acdS gene had reduced disease

symptoms. Robison et al. (2001) also developed

transgenic tomatoes expressing the the acdS gene

from Enterobacter cloacae UW4 activated by any of

the promoters: 35S CaMV, rolD or prb-1b. These

plants were studied for their response towards wilt

caused by Verticillium dahliae. Remarkable reduction

was observed in the symptoms of Verticillium wilt in

rolD- and prb-1b-propelled acdS transformants due to

reduced ethylene synthesis. These observations sug-

gest that tolerance to various diseases caused by

phytopathogens can be achieved through engineering

plants for lower disease-related ethylene synthesis (via

acdS gene expression).

Delayed fruit ripening by decreasing ethylene

synthesis

Ethylene functions as an endogenous regulator of fruit

ripening. By inserting the acdS gene from Pseudomo-

nas chloraphis 6G5 into tomato plants under the

control of the 35S CaMV promoter significantly

delayed the fruit ripening (Klee et al. 1991). More-

over, decreasing ethylene synthesis in transgenic

plants exhibited no significant phenotypic changes.

Fruits from transgenic plants displayed delayed

ripening and remained firm for at least six weeks

longer compared to the fruits from non-transgenic

plants. Reed et al. (1995) used transgenic tomato lines

generated by Klee et al. (1991) and studied them for

delayed ripening of fruits and obtained similar results.

Tomatoes also have inherent ACC deaminase activity

and this activity varies during ripening of the fruit

(Plett et al. 2009). Thus, either introduction of a

bacterial acdS gene or alteration in the expression of

plant’s intrinsic acdS gene may be employed to delay

the time of fruit ripening by reduction of excessive

ethylene production.

Regulation of the ACC deaminase gene

The acdS gene is present in numerous soil bacteria

such as Enterobacter cloacae UW4 and Pseudomonas

putida UW4. This gene is regulated mainly by leucine-

responsive regulatory protein (LRP) (Li and Glick

2001; Cheng et al. 2008). In Bradyrhizobium japon-

icum USDA110 and Rhizobium leguminosarum bv.

viciae 128C53 K, the acdS genes are regulated by an

LRP-like protein and r70 promoter (Kaneko et al.

2002; Ma et al. 2003). However, in some species, such

as Mesorhizobium loti MAFF303099, it is under the

transcriptional control of the N2-fixing regulator, nifA

(Nukui et al. 2006).

In Pseudomonas putida UW4, the DNA sequence

for the region upstream of the acdS gene contains a

cyclic AMP receptor protein (CRP) binding site, a

fumarate-nitrate reduction regulatory (FNR) protein-

binding site (known as anaerobic transcriptional

regulator), a promoter sequence controlling the ACC

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deaminase regulatory gene (acdR; encode Lrp) and a

LRP binding site. All of these interact and engage in

transcriptional regulation of acdS gene (Grichko et al.

2000; Li and Glick 2001). Cheng et al. (2008)

observed that AcdB protein interacts with ACC and

forms a complex with octamer unit of Lrp protein

which binds to the upstream region of acdS and further

initiates transcription of acdS gene. When ACC

deaminase is formed it decomposes ACC to generate

ammonia and a-ketobutyrate (which is a precursor of

leucine), as the concentration of leucine increases in

the cell, it binds to the LRP octamer leading to its

dissociation into an inactive dimeric form. This

dissociation causes the switching off the transcription

of acdS gene. It was observed that in some bacteria the

CRP and FNR binding sites were not present but they

can effectively transcribe acdS gene. However, the

insight of how these proteins and transcription regu-

lator interact is not well understood but, on the basis of

available published data, a representation of transcrip-

tional regulation of acdS gene for P. putida UW4 has

been generated and illustrated in Fig. 1.

In some species of Rhizobia, such as Mesorhizobi-

um loti MAFF303099, the acdS gene is under the

control of a nifA promoter (which is a N2 fixation

promote) and is expressed within legume nodules

(Uchiumi et al. 2004; Nukui et al. 2006). In case of

Mesorhizobium loti, the DNA sequence for the region

upstream of the acdS and nifH contained nifA1 and

nifA2 (N2 fixation regulators) and a r54 RNA poly-

merase sigma recognition site. The N2 fixation regu-

lator, nifA2, encodes NifA2 protein which interacts

with r54 RNA polymerase sigma recognition factor

and initiates transcription of acdS gene (Nukui et al.

2006). The nifA1 is also involved in increasing the

transcription of acdS gene and, as is evident from the

studies of Nukui et al. (2006), the disruption of nifA1

enhances expression of the acdS transcripts to some

extent and faintly suppresses the expression of nifH.

On the basis of published reports, a representation of

transcriptional regulation of acdS gene for Mesorhiz-

obium loti has been generated and illustrated in Fig. 2.

It was assumed that the expression of acdS gene within

N2-fixing nodules involves diminishing the effect of

senesce induced by ethylene in the nodules so that the

endurance of nodules increases which, in turn,

elevates the concentration of fixed N in the nodules.

To date, there are only a few reports of plant-

encoded acdS genes, such as in Arabidopsis, poplar

and tomato (McDonnell et al. 2009; Plett et al. 2009).

Fig. 1 The transcription regulation of acdS gene expression in

Pseudomonas putida UW4 and in a wide range of bacteria. The

schematic shows the interaction of different promoters and their

products involved in transcription of this gene. Various

abbreviations which are used, stand for following—acdR ACC

deaminase regulatory gene; LRP leucine-responsive regulatory

protein; AcdB protein encoding glycerophosphoryl diester

phosphodiesterase and form complex with ACC; FNR fuma-

rate-nitrate reduction regulatory protein; CRP cyclic AMP

receptor protein binding site; acdS: ACC deaminase structural

gene; LEU leucine

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The putative acdS gene from Arabidopsis was cloned

in pCAMBIA vector and transformed into Arabi-

dopsis. It was constitutively expressed under the

control of 35S CaMV promoter. The plant-encoded

acdS genes played a vital role in regulating ethylene

balance in plants (McDonnell et al. 2009). The exact

regulation of acdS gene in plants is unknown and

efforts should be made on unveiling the mechanism

acdS gene regulation in plants.

ACC deaminase activity in transgenic plants

Various transgenic plants overexpressing acdS gene

have been studied for their expression. Transgenic

tomato plants overexpressing acds gene under the

control of 35S CaMV promoter in presence of Cu

produced 3.8 mmol a-ketobutyrate/g protein/h in leaf

tissue. Similarly, transgenic tomato plants over-

expressing acds gene under the control in rolD

promoter in presence of Ni produced 3.5 mmol a-

ketobutyrate/g protein per h in root tissue (Grichko

et al. 2000). Similar results have been reported for a

transgenic tomato overexpressing the acdS gene from

Enterobacter cloacae UW4 under the control of

35S CaMV promoter. Here an ACC deaminase activ-

ity of 60 nmol a-ketobutyrate/mg protein per min was

in leaf tissues measured during Verticillium infection.

These plants expressed ACC deaminase activity of

42 nmol a-ketobutyrate/mg protein per min in root

tissues and 5 nmol a-ketobutyrate/mg protein per min

in leaf tissues with rolD and prb-1b promoters,

respectively (Robison et al. 2001). In transgenic

canola plants, a acdS gene under the control of

35S CaMV promoter resulted in maximum enzyme

activity of 0.58 nmol a-ketobutyrate/g protein per h in

leaf tissues. These plants expressed enzyme activity of

0.99 nmol a-ketobutyrate/g protein per h in root

tissues and 0.53 nmol a-ketobutyrate/g protein per h

in leaf tissues with rolD and prb-1b promoters,

respectively (Sergeeva et al. 2006). Transgenic tomato

and canola plants overexpressing acdS gene under the

control of prb-1b promoter exhibited lower ACC

deaminase activity as compared to the activity of same

gene under the control of 35S CaMV and rolD

promoter (Robison et al. 2001; Grichko et al. 2005;

Sergeeva et al. 2006). This trend of lower expression

of acdS gene with prb-1b promoter irrespective of

stressed or unstressed condition infers that the prb-1b

promoter is inappropriate for the expression of acdS

gene.

Transgenic plants overexpressing a bacterial or

plant acdS gene had a stable and functionally active

enzyme. Likewise, transgenic Arabidopsis plant over-

expressing its acdS gene demonstrated enzyme activ-

ity of 650 nmol a-ketobutyrate/mg protein per h in

leaf tissues (McDonnell et al. 2009). Different trans-

genic plants overexpressing acdS gene from plant and

bacterial origin and their respective ACC deaminase

activities are presented in Table 2.

Fig. 2 Transcription regulation of acdS gene in nitrogen fixing

bacteria Mesorhizobium loti MAFF303099. The schematic

shows the interaction of different promoters and their products

involved in transcription of this gene. Various short terms which

are used, stand for following, nifA1 and nifA2: transcriptional

activator of nitrogenase genes; NifA2: NifA protein binding

site; a r54 RNA polymerase sigma recognition factor and acdS:

ACC deaminase structural gene; nifH: encoding nitrogenase

reductase subunit of nitrogenase enzyme

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123

Conclusion and future prospects

Plants are exposed to numerous biotic and abiotic

conditions in the environment that enhance ethyl-

ene-induced stress thereby hindering plant growth.

A large number of transgenic plants overexpressing

a acdS gene from plant and bacterial origin have

been developed to prevent this stress. The perfor-

mance of the transgenic plants in combating stress-

ful conditions was at equal to that of plants treated

with bacteria having ACC deaminase activity. The

major advantage of transgenic plants overexpressing

a acdS gene as compared to non-transgenic plants

treated with ACC deaminase-containing bacteria is

that the transgenic plants will constitutively express

the gene under any environmental condition,

whereas the ACC deaminase-containing bacteria

(associated with plant roots) on exposure to harsh

environmental conditions (cold, high temperature,

heavy metal, salinity, flooding, drought) are mostly

unable to survive these conditions. Hence, research

should be focused to isolate new bacteria having

ACC deaminase activity that can tolerate various

stresses. Such bacteria can be used as biofertilizers

for crops grown under different environmental

conditions to combat stress related to endogenous

ethylene production. Even the acdS genes from

these bacteria can be used as an efficient source for

developing transgenic plants.

Although, several bacteria possessing ACC deam-

inase have been studied, our knowledge of factors

regulating the transcription of this gene is still

inadequate especially for some bacteria possessing

ACC deaminases in combination with N2-fixing

ability. Therefore, efforts are required to unveil its

regulation mechanism. Since, there are reports of acdS

gene from plants in Arabidopsis, poplar and tomato it

is assumed that other plants may contain the same

gene. Thus, research should be undertaken to explore

other plant-associated acdS genes. The search for new

ACC deaminase-possessing bacteria and to engineer

plants for enviable traits should go hand in hand as a

plausible solution to overcome ethylene-generated

stress conditions.

Acknowledgments The author I.G.M. thankfully acknowl-

edges financial support received from Science and Engineering

Research Board (Grant # SB/FT/LS-374/2012), Department of

Science and Technology, New Delhi, India.

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Table 2 List of transgenic plants overexpressing ACC deaminase gene and respective activities

Transgenic plant

expressing ACC

deaminase gene

ACC deaminase activity Reference

Tomato (i) 3.8 mmol/g protein/h in leaf tissue (with 35S CaMV promoter in presence of Cu)

(ii) 3.5 mmol/g protein/h in root tissue (with rolD promoter in presence of Ni)

Grichko et al.

(2000)

Tomato (i) 60 nmol/mg protein/min in leaf tissue (with 35S CaMV promoter in presence of

Verticillium infection) (ii) 42 nmol/mg protein/min in root tissue (with rolD

promoter in presence Verticillium infection) (iii) 5 nmol/mg protein/min in leaf

tissue (with prb-1b promoter in presence Verticillium infection)

Robison et al.

(2001)

Tomato (i) 0.805 mmol/g protein/h in leaf tissue (with 35S CaMV promoter) (ii)

0.830 mmol/g protein/h in root tissue (with rolD promoter) (iii) 0.151 mmol/g

protein/h in leaf tissue (with prb-1b promoter)

Grichko et al.

(2005)

Canola (i) 0.58 nmol/g protein/h in leaf tissue (with 35S CaMV promoter in presence of

NaCl) (ii) 0.99 nmol/g protein/h in root tissue (with rolD promoter in presence of

NaCl) (iii) 0.53 nmol/g protein/h in leaf tissue (with prb-1b promoter in presence

of NaCl)

Sergeeva et al.

(2006)

Arabidopsis thaliana (i) 650 nmol/mg protein/h McDonnell et al.

(2009)

Biotechnol Lett

123

from polluted soils and containing 1-aminocyclopropane-

1-carboxylate deaminase. Can J Microbiol 47:642–652

Belimov A, Dodd IC, Safronova VI, Davies WJ (2009) ACC

deaminase-containing rhizobacteria improve vegetative

development and yield of potato plants grown under water-

limited conditions. Asp Appl Biol 98:163–169

Burd GI, Dixon DG, Glick BR (2000) Plant growth-promoting

bacteria that decrease heavy metal toxicity in plants. Can J

Microbiol 46:237–245

Cheng Z, Park E, Glick BR (2007) 1-Aminocyclopropane-1-

carboxylate deaminase from Pseudomonas putida UW4

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Cheng Z, Duncker BP, McConkey BJ, Glick BR (2008) Tran-

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Dastager SG, Deepa CK, Pandey A (2010) Isolation and char-

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sp NII-0909 and its interaction with cowpea. Plant Physiol

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Farwell AJ, Vesely S, Nero V, Rodriguez H, McCormack K,

Shah S, Dixon DG, Glick BR (2007) Tolerance of trans-

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growth-promoting bacteria to flooding stress at a metal-

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Grichko VP, Glick BR (2001) Flooding tolerance of transgenic

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Grichko VP, Filby B, Glick BR (2000) Increased ability of

transgenic plants expressing the bacterial enzyme ACC

deaminase to accumulate Cd Co, Cu, Ni, Pb and Zn.

J Biotechnol 81:45–53

Grichko VP, Glick BR, Grishko VI, Pauls KP (2005) Evaluation

of tomato plants with constitutive, root-specific, and stress-

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Physiol 52:359–364

Holguin G, Glick BR (2001) Expression of the ACC deaminase

gene from Enterobacter cloacae UW4 in Azospirillum

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Hontzeas N, Zoidakis J, Glick BR, Abu-Omar MM (2004)

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Li J, Glick BR (2001) Transcriptional regulation of the Enter-

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Madhaiyan M, Poonguzhali S, Ryu J, Sa T (2006) Regulation of

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Mayak S, Tirosh T, Glick BR (2004) Plant growth-promoting

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