ACC Deaminase Gene Research Articles

Heterologous expression of ACC deaminase gene in Pelargonium graveolens showed elevated tolerance to chromium stress.

An essential aromatic plant, Pelargonium graveolens, does not grow well in areas where chromium contamination is a problem. Because of oxidative stress and the collapse of the photosynthetic system, crops frequently sustain severe damage. The production of excess ethylene, known as stress ethylene, which is detrimental to plant growth, the formation of roots, and early senescence, is also increased by heavy metal exposure. The effectiveness of the 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase gene in transgenic Pelargonium graveolens under the control of CaMV 35S promoter was investigated to lessen the stress ethylene during chromium stress. Chromium was administered as potassium dichromate (K2Cr2O7) at four distinct concentrations (100µM, 200µM, 300µM, and 500µM) to transgenic and wild-type P. graveolens and stress-induced physiological changes were monitored. Transgenic P. graveolens demonstrated greater tolerance to chromium stress than wild-type P. graveolens, as evidenced by higher leaf-relative water content, chlorophyll content, CO2 absorption, transpiration rate, stomatal conductance, proline buildup, and antioxidant activity. The L1, L5, and L7, ACC deaminase-expressing transgenic lines also show a drop in ACC content during chromium stress, which subsequently lowered ethylene synthesis. Therefore, the reported transgenic P. graveolens lines having the ACC deaminase gene could be useful resources for growing in chromium-prone regions.

The genome, pangenome, and physiological analysis of Leclercia adecarboxylata (kcgeb_e1), a plant growth-promoting bacterium

Plant growth-promoting bacteria (PGPB) as biofertilizer plays an important role in agriculture practices. In this study, we isolated and identified plant-associated bacteria Leclercia adecarboxylata (kcgeb_e1) from the root region of the halophytic plant Sesuvium verrucosum. We tested its physiological activity and the effect of inoculation, with and without salt, on photosynthesis using Cajanus cajan. Further, we sequenced the whole genome of L. adecarboxylata (kcgeb_e1) and carried out pangenome analysis with 12 other genomes of the same species, which highlights unique genes enriched for pathways involved in abiotic stress tolerance (salinity, drought and heat) and carbohydrate transport. Moreover, gene families involved in abiotic stress tolerance, host adhesion, and transport were under positive selection (e.g., Aldo/keto reductase family, Hemagglutinin, Porin, and sugar transport). We observed a loss of ACC deaminase gene in this pangenome; however, this strain can still produce 1-aminocyclopropane-1-carboxylate (ACC), an enhancer of abiotic stress, which suggests that its homologue, d-cysteine sulfatase, has a bifunctional activity. In addition, this strain has Indole acetic acid (IAA) and phosphate solubilization activity. Combining these findings with the efficiency of colonizing the root surface of Solanum lycopersicum, this strain showed remarkable enhancement of photosynthesis, comparing control to inoculated plants. This increase in photosynthesis is consistent with an increase in sucrose under salt treatment, but not in glucose and fructose, which acts as a sensor in opposing the negative effect of salinity and promoting sustainable growth. Given all this, our study suggests that this PGPB can act as a biofertilizer for sustainable agriculture.

Claroideoglomus etunicatum affects the structural and functional genes of the rhizosphere microbial community to help maize resist Cd and La stresses

Arbuscular mycorrhizal fungi (AMF) and plant rhizosphere microbes reportedly enhance plant tolerance to abiotic stresses and promote plant growth in contaminated soils. The co-contamination of soil by heavy metals (e.g., Cd) and rare earth elements (e.g., La) represents a severe environmental problem. Although the influence of AMF in the phytoremediation of contaminated soils is well documented, the underlying interactive mechanisms between AMF and rhizosphere microbes are still unclear. We conducted a greenhouse pot experiment to evaluate the effects of AMF (Claroideoglomus etunicatum) on maize growth, nutrient and metal uptake, rhizosphere microbial community, and functional genes in soils with separate and combined applications of Cd and La. The purpose of this experiment was to explore the mechanism of AMF affecting plant growth and metal uptake via interactions with rhizosphere microbes. We found that C. etunicatum (i) significantly enhanced plant nutritional level and biomass and decreased metal concentration in the co-contaminated soil; (ii) significantly altered the structure of maize rhizosphere bacterial and fungal communities; (iii) strongly enriched the abundance of carbohydrate metabolism genes, ammonia and nitrate production genes, IAA (indole-3-acetic acid) and ACC deaminase (1-aminocyclopropane-1-carboxylate) genes, and slightly altered the abundance of P-related functional genes; (iv) regulated the abundance of microbial quorum sensing system and metal membrane transporter genes, thereby improving the stability and adaptability of the rhizosphere microbial community. This study provides evidence of AMF improving plant growth and resistance to Cd and La stresses by regulating plant rhizosphere microbial communities and aids our understanding of the underlying mechanisms.

Soybean abiotic stress tolerance is improved by beneficial rhizobacteria in biosolids-amended soil

Soybean responds to heat and water deficit by producing ethylene, which in high concentrations reduces plant biomass. One way for soybean to tolerate stress is to associate with rhizobacteria that lower the ethylene concentration by hydrolyzing the molecular precursor with the extracellular enzyme 1-aminocyclopropane-1-carboxylate deaminase (ACC deaminase). Organic fertilizer could enhance soybean stress tolerance by providing essential nutrients to the plant and substrates to rhizobacteria with ACC deaminase activity. The objectives of this study were 1) to evaluate the effects of organic fertilizer and mineral N fertilizer on rhizosphere ACC deaminase activity and ethylene production of soybean exposed to heat or water deficit and subsequently 2) determine if fertilizer-induced responses improve soybean tolerance to heat and water deficit. Soybean was grown in soil amended with organic fertilizer (biosolids or anaerobic digestate) or with mineral N fertilizer (urea) for 9 wk in a greenhouse, then exposed to no stress, heat stress or water deficit for 7 d. In digestate-amended soils, we detected more ACC deaminase (acdS) gene copies in the rhizosphere, while biosolid-treated soil had 33% greater ACC deaminase activity in the rhizosphere than the soil receiving mineral N fertilizer. The ACC deaminase activity was negatively correlated with ethylene production from the soybean-soil system. At the same time, soybean biomass was less affected by heat or water deficit in biosolids and digestate-treated soils, as they were 23–36% taller and had 11–22% more biomass than soybean receiving mineral N fertilizer. The increase in acdS gene copies and ACC deaminase activity in the rhizosphere of organically-fertilized soils has potential for improving soybean tolerance to heat and water deficit.

Formulation of biofertilizer for improving growth and yield of wheat in rain dependent farming system

Low and erratic rainfall can cause a significant reduction in crop yields in agriculture systems that rely exclusively on rain water. Some plant growth promoting rhizobacteria (PGPR) capable of producing 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase can mitigate the negative impact of water stress on plant in rainfed agriculture through modulation of plant stress hormone ethylene. The present study was conducted in rainfed areas to demonstrate the potential of PGPR with ACC-deaminase activity to enhance the growth and yield of wheat ( Triticum aestivum L.) under field conditions. Previously isolated bacterial strains ( Serratia odorifera CC7, Aerococcus viridans CK3 and Serratia proteamaculans R20) having in-vitro ACC deaminase activity were used for inoculation. Peat, compost and biochar were used as carrier material for the formulation of biofertilizer. Our results show that application of the compost biofertilizer increased plant biomass up to 27% and grain yield up to 33.3% compared with uninoculated control. Maximum N and P content in grain was observed 24.7 % and 25.8% respectively. Maximum ACC-deaminase activity of 821 nmol g −1 biomass h −1 was observed with strain CC7, while root colonization activity was also highest in case of strain CC7 i.e 6.2 × 10 6 compared to other strains. All the strains showed positive response to phosphate solubilization activity as well. Furthermore, ACC deaminase gene isolated from CC7 strain showed 79.1% homology to the ACC deaminase gene of Achromobacter , 83.9% homology to the ACC deaminase gene of Pseudomonas . These findings indicate that PGPR isolated from rainfed area can be used for biofertilizer formulation which could be very effective to increase the production of wheat in rainfed agriculture system. • PGPR isolated from rainfed areas can be used for biofertilizer formulation for increased yield of wheat. • Peat, compost and biochar were used a carrier material for formulation of biofertilizer. • Compost based biofertilizer increased the growth and yield of wheat under natural conditions. • The N and P content of the wheat grain increased upon use of compost biofertilizer.

Induction of drought tolerance in Pennisetum glaucum by ACC deaminase producing PGPR- Bacillus amyloliquefaciens through Antioxidant defense system

Rhizobacteria from pearl millet were screened to produce 1-aminocyclopropane-1-carboxylate (ACC) deaminase and to evaluate its role in alleviating drought stress. Amongst 96 isolates, 28 were positive for ACC deaminase production, with MMR04 offering maximum activity of 2196.23 nmol of α-ketobutyrate produced mg–1 of protein h–1. The ACC deaminase producing rhizobacteria with multiple beneficial properties along with root colonization and non-pathogenic were selected [Bacillus amyloliquefaciens (MMR04), Bacillus subtilis (MMR18) and Stenotrophomonas maltophilia (MMR36)] to confirm the presence of ACC deaminase gene. A significant enhancement in seed germination (91.75%) and seedling vigor (1213.73) was noted upon seed treatment with MMR04 and hence further evaluated for its ability to induce drought stress. The seed treatment with MMR04 improved plant growth parameters and total chlorophyll and RWC in plants grown under severe drought stress (G5) conditions compared to control plants. In addition, MMR04 seed treatment enhanced proline, APX and SOD activity while decreased the MDA content up to 2.3 fold compared to untreated plants (G5). Gene expression studies revealed a significant decrease of 3.3 and 1.8 fold in the relative expression of drought-responsive (DREB-1E) and ethylene-responsive factor (ERF-1B) marker genes, respectively and an increase of 2.2 and 2.9 fold in the relative expression of APX1 and SOD1, respectively in MMR04 treated plants grown under G5 conditions over control. The results confirmed that ACC deaminase producing B. amyloliquefaciens MMR04 could defend the pearl millet plants against drought stress through an antioxidative system, thereby warranting its application in drought stress management.

Salt and drought stress tolerance with increased biomass in transgenic Pelargonium graveolens through heterologous expression of ACC deaminase gene from Achromobacter xylosoxidans

Salt and drought stress tolerance with increased biomass in transgenic Pelargonium graveolens through heterologous expression of ACC deaminase gene from Achromobacter xylosoxidans

Enhancing the 1-Aminocyclopropane-1-Carboxylate Metabolic Rate of Pseudomonas sp. UW4 Intensifies Chemotactic Rhizocompetence.

1-aminocyclopropane-1-carboxylic acid (ACC) is a strong metabolism-dependent chemoattractant for the plant beneficial rhizobacterium Pseudomonas sp. UW4. It is unknown whether enhancing the metabolic rate of ACC can intensify the chemotaxis activity towards ACC and rhizocompetence. In this study, we selected four promoters to transcribe the UW4 ACC deaminase (AcdS) gene in the UW4 ΔAcdS mutant. PA is the UW4 AcdS gene promoter, PB20, PB10 and PB1 are synthetic promoters. The order of the AcdS gene expression level and AcdS activity of the four strains harboring the promoters were PB20 > PA > PB10 > PB1. Interestingly, the AcdS activity of the four strains and their parent strain UW4 was significantly positively correlated with their chemotactic activity towards ACC, rhizosphere colonization, roots elongation and dry weight promotion. The results released that enhancing the AcdS activity of PGPRenable them to achieve strong chemotactic responses to ACC, rhizocompetence and plant growth promotion.

Super-Agrobacterium ver. 4: Improving the Transformation Frequencies and Genetic Engineering Possibilities for Crop Plants.

Agrobacterium tumefaciens has been utilized for both transient and stable transformations of plants. These transformation methods have been used in fields such as breeding GM crops, protein production in plant cells, and the functional analysis of genes. However, some plants have significantly lower transient gene transfer and stable transformation rates, creating a technical barrier that needs to be resolved. In this study, Super-Agrobacterium was updated to ver. 4 by introducing both the ACC deaminase (acdS) and GABA transaminase (gabT) genes, whose resultant enzymes degrade ACC, the ethylene precursor, and GABA, respectively. A. tumefaciens strain GV2260, which is similar to other major strains (EHA105, GV3101, LBA4404, and MP90), was used in this study. The abilities of the Super-Agrobacterium ver. 4 were evaluated in Erianthus ravennae, Solanum lycopersicum “Micro-Tom,” Nicotiana benthamiana, and S. torvum. Super-Agrobacterium ver. 4 showed the highest T-DNA transfer (transient transformation) frequencies in E. ravennae and S. lycopersicum, but not in N. benthamiana and S. torvum. In tomato, Super-Agrobacterium ver. 4 increased the stable transformation rate by 3.6-fold compared to the original GV2260 strain. Super-Agrobacterium ver. 4 enables reduction of the amount of time and labor required for transformations by approximately 72%, and is therefore a more effective and powerful tool for plant genetic engineering and functional analysis, than the previously developed strains. As our system has a plasmid containing the acdS and gabT genes, it could be used in combination with other major strains such as EHA105, EHA101, LBA4404, MP90, and AGL1. Super-Agrobacterium ver. 4, could thus possibly be a breakthrough application for improving basic plant science research methods.

Isolation, identification, and detection of ACC deaminase gene-encoding rhizobacteria from rhizosphere of stressed pineapple

ACC deaminase is a microbial cytoplasmic enzyme that cleaves ACC, a precursor of ethylene, in the stressed plant. The aims of this study were to isolate, identify, and detect the presence of ACC deaminase gene-encoding rhizobacteria from the rhizospheric soil of pineapple plants that have been exposed to abiotic and biotic stress, specifically herbicide, flooding, and Phytophthora spp. stress. A total of 49 rhizobacterial isolates were obtained, seven of which were observed for their growth on DF medium containing 3 mM L-1 ACC. The four best-growing isolates were selected for genomic DNA extraction. They were molecularly identified as Stenotrophomonas maltophilia (3), Burkholderia territorii (2A), Pseudomonas oryzihabitans (5B), and Bacillus tropicus (1E). A set of primers, 105F-acdS 5’-TGCCAAGCGTGAAGACTGC-3’ and 244R-acdS 5’-GGGTCTGGTTCGACTGGAT-3’, were constructed to amplify the ACC deaminase gene (acdS). Based on melt peak curve analysis, four products appeared to show a specific single peak at 86, 89, 87, and 89.5°C, indicating a single product was produced. In addition, a Blast search showed that these four products met the ACC deaminase feature and their acdS sequences were clustered into an ancestral group compared with the bacterial strains deposited in GenBank. These results suggest that ACC deaminase gene-encoding rhizobacteria from a pineapple plantation of tropical origin may affect the acdS sequences and may contribute to the host plant’s stress tolerance.

Unravelling the biochemistry and genetics of ACC deaminase-An enzyme alleviating the biotic and abiotic stress in plants

The enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase is known for alleviating the adverse effects of ethylene generated in response various stressors. Phylogenetic analysis of corresponding gene encoding ACC degrading enzyme (acds) reveals their occurrence in diverse group of bacteria and fungi. The transcription of acds gene is tightly regulated and expresses differentially under different environmental conditions. Moreover, ACC metabolizing enzyme is an inductive enzyme which expressed only in presence of its substrate, ACC. This microbial enzyme has prominent role as cost-effective and eco-friendly adjuncts in sustainable agricultural system because it catalysed the breakdown of immediate precursor of ethylene, i.e. ACC into α-ketobutyrate and ammonia, and thereby declined the concentration of ethylene and its associated negative effects on growth and development of plants growing under various biotic and abiotic stressful conditions. Therefore, the present review attempts to summarizes the knowledge regarding biochemistry and genetics of ACC deaminase enzyme, prevalence and regulation of corresponding ACC deaminase gene (acds) across different groups of microbes as well as future research approaches to create transgenic crops containing microbial acds gene to withstand variety of stressful conditions.

Modulation of salt tolerance in Thai jasmine rice (Oryza sativa L. cv. KDML105) by Streptomyces venezuelae ATCC 10712 expressing ACC deaminase

1-Aminocyclopropane-1-carboxylate (ACC) deaminase is a plant growth promoting (PGP) trait found in beneficial bacteria including streptomycetes and responsible for stress modulation. The ACC deaminase gene, acdS, of S. venezuelae ATCC 10712 was cloned into an expression plasmid, pIJ86, to generate S. venezuelae/pIJ86-acdS. Expression of acdS and production of ACC deaminase of S. venezuelae/pIJ86-acdS were significantly higher than the unmodified strain. The ACC deaminase-overexpressing mutant and the wild type control were inoculated into Thai jasmine rice (Oryza sativa L. cv. KDML105) under salt stress conditions. S. venezuelae on its own augmented rice growth and significantly increased more tolerance to salinity by reduction of ethylene, reactive oxygen species (ROS) and Na+ contents, while accumulating more proline, total chlorophyll, relative water content (RWC), malondialdehyde (MDA), and K+ than those of uninoculated controls. The overproducer did not alter chlorophyll, RWC, or MDA further–while it did boost more shoot weight and elongation, and significantly regulated salt tolerance of rice by increasing proline and reducing ethylene and Na+ contents further than that of the wild type. This work is the first illustration of the beneficial roles of S. venezuelae to enhance plant fitness endophytically by promotion of growth and salt tolerance of rice.

Pseudomonas veronii KJ mitigates flood stress-associated damage in Sesamum indicum L.

Physiological characteristics of terrestrial plants are severely affected by waterlogging stress, leading to low photochemical efficiency of leaves and retarded growth and development. Plant growth-promoting rhizobacteria contain the acdS gene, which encodes for the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase. ACC deaminase cleaves the substrate ACC to produce α-ketobutyrate and ammonia and mitigates the adverse effect of prolonged water stress. The aim of this study was to characterize ACC deaminase-producing rhizobacteria and evaluate their effects on sesame (Sesamum indicum L.) under waterlogging stress condition. The rhizobacterium Pseudomonas KJ was characterized on the basis of sequencing of the partial 1501 bp fragment of 16S rDNA amplicon and confirmed as Pseudomonas veronii KJ. ACC-supplemented minimal medium revealed the phenotypic identification of acdS gene. The nucleotide sequence (1001 bp) of ACC deaminase gene of P. veronii KJ was also confirmed. We used P. veronii KJ as a bioinoculant in waterlogging stress and monitored the growth and developmental characteristics of sesame plants, including leaf chlorophyll fluorescence signals, concentration of chlorophyll, root and shoot length, and fresh and dry biomass in stressed versus unstressed plants. Plants treated with P. veronii KJ significantly (P ≤ 0.05) mitigated the waterlogging stress-related damage. Thus, the rhizobacterium Pseudomonas veronii KJ may be considered as a commendable addition to the consortium of beneficial microbes for its ability to reduce waterlogging stress-related damage in sesame plants.

1-Aminocyclopropane-1-carboxylate deaminase producers associated to maize and other Poaceae species

BackgroundComplex plant-microbe interactions have been established throughout evolutionary time, many of them with beneficial effects on the host in terms of plant growth, nutrition, or health. Some of the corresponding modes of action involve a modulation of plant hormonal balance, such as the deamination of the ethylene precursor 1-aminocyclopropane-1-carboxylate (ACC). Despite its ecological importance, our understanding of ACC deamination is impaired by a lack of direct molecular tools. Here, we developed PCR primers to quantify the ACC deaminase gene acdS and its mRNA in soil communities and assessed acdS+ microorganisms colonizing maize and other Poaceae species.ResultsEffective acdS primers suitable for soil microbial communities were obtained, enabling recovery of bona fida acdS genes and transcripts of diverse genetic backgrounds. High numbers of acdS genes and transcripts were evidenced in the rhizosphere of Poaceae, and numbers fluctuated according to plant genotype. Illumina sequencing revealed taxonomic specificities of acdS+ microorganisms according to plant host. The phylogenetic distance between Poaceae genotypes correlated with acdS transcript numbers, but not with acdS gene numbers or the genetic distance between acdS functional groups.ConclusionThe development of acdS primers enabled the first direct analysis of ACC deaminase functional group in soil and showed that plant ability to interact with soil-inhabiting acdS+ microorganisms could also involve particular plant traits unrelated to the evolutionary history of Poaceae species.

Improvement of Cupriavidus taiwanensis Nodulation and Plant Growth Promoting Abilities by the Expression of an Exogenous ACC Deaminase Gene.

Several rhizobial strains possess the ability to modulate leguminous plants ethylene levels by producing the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase. While the effect of ACC deaminase has been studied in several rhizobia belonging to the Alphaproteobacteria class, not much is understood about its impact in the nodulation abilities of rhizobia belonging to the Betaproteobacteria class, which are common symbionts of Mimosa species. In this work, we report the impact of ACC deaminase production by the Betaproteobacterium, Cupriavidus taiwanensis STM894, and its role in the nodulation of Mimosa pudica. C. taiwanensis STM894 was studied following its transformation with the plasmid pRKACC, containing an ACC deaminase gene. The expression of the exogenous ACC deaminase led to increased nodulation and M. pudica growth promotion by C. taiwanensis STM894. These results indicate that ACC deaminase plays an important role in modulating ethylene levels that inhibit the nodulation process induced by both rhizobia belonging to the Alpha and Betaproteobacteria class.

Population diversity of bacterial endophytes from jute (Corchorus olitorius) and evaluation of their potential role as bioinoculants

Endophytes are bacterial or fungal organisms associated with plants in an obligate or facultative manner. In order to maintain a stable symbiosis, many of the endophytes produce compounds that promote plant growth and help them adapt better to the environment. This study was conducted to explore the potential of jute bacterial endophytes for their growth promotion ability in direct and indirect ways. A total of 27 different bacterial species were identified from different varieties of a jute plant (Corchorus olitorius) and different parts of the plant (leaf, root, seed, and seedling) based on 16S rRNA gene sequence. Two of the isolates showed ACC deaminase activity with Staphylococcus pasteuri strain MBL_B3 and Ralstonia solanacearum strain MBL_B6 producing 18.1 and 8.08 μM mg−1 h−1 α-ketobutyrate respectively while eighteen had the ACC deaminase gene (acdS). Fourteen were positive for siderophore activity while Kocuria sp. strain MBL_B19 (133.36 μg/ml) and Bacillus sp. strain MBL_B17 (124.72 μg/ml) showed high IAA production ability. Seven bacterial strains were able to fix nitrogen with only one testing positive for nifH gene. Five isolates exhibited phosphorus utilization ability with Bacillus sp. strain MBL_B17 producing 218.47 μg P/ml. Three bacteria were able to inhibit the growth of a phytopathogen, Macrophomina phaseolina and among them Bacillus subtilis strain MBL_B4 was found to be the most effective, having 82% and 53% of relative inhibition ratio (RIR) and percent growth inhibition (PGI) values respectively. Nine bacteria were tested for their in vivo growth promotion ability and most of these isolates increased seed germination potential and vigour index significantly. Bacillus subtilis strain MBL_B13 showed 26.8% more vigour index than the control in which no bacterial inoculum was used. All inoculants were found to increase the dry weight of jute seedlings in comparison to the control plants and the most increase in fresh weight was found for Staphylococcus saprophyticus strain MBL_B9. Staphylococcus pasteuri strain MBL_B3 exhibited diverse in vitro growth promotion activity and significant growth promoting effect in in vivo pot experiments. These bacterial strains with plant growth enhancing abilities have the potential to be used as bioinoculants.

Biocontrol of Fusarium wilt of Capsicum annuum by rhizospheric bacteria isolated from turmeric endowed with plant growth promotion and disease suppression potential

In the present study, 129 rhizospheric bacteria isolated from Curcuma longa were screened for their antagonistic potential against six fungal phytopathogens. Among them, 32 isolates that showed significant antagonistic potential were screened for their in vitro plant growth promoting (PGP) traits. The identification of potential isolates was confirmed by 16S rRNA gene sequencing and results revealed Bacillus as the dominant genus followed by Staphylococcus, Pseudomonas, Sphingomonas and Achromobacter. Based on the antagonistic activity and PGP traits; two strains (BPSRB4 and BPSRB14), identified as Bacillus amyloliquefaciens, were further tested for their in vivo PGP and disease suppression potential on Capsicum annuum seedlings under greenhouse conditions. The results demonstrated that BPSRB4 and BPSR14 strains suppress fungal pathogen infection and promote plant growth. Further, the BPSRB4 strain was positive for the production of the phytohormone indole acetic acid (IAA) detected by thin layer chromatography (TLC). In addition, nitrogen fixation and plant growth promotion activity were also confirmed by amplification and sequencing of nitrogen fixation gene (nifH) and ACC (1-aminocyclopropane-1-carboxylate) deaminase (acdS) gene from strains BPSRB4 and BPSRB14. The present study demonstrated that the B. amyloliquefaciens strains BPSRB4 and BPSR14 possess antagonistic activity and PGP potential which could be explored for the development of biofertilizers and biocontrol agents for the growth of chilli seedlings.

Role and Regulation of ACC Deaminase Gene in Sinorhizobium meliloti: Is It a Symbiotic, Rhizospheric or Endophytic Gene?

Plant-associated bacteria exhibit a number of different strategies and specific genes allow bacteria to communicate and metabolically interact with plant tissues. Among the genes found in the genomes of plant-associated bacteria, the gene encoding the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase (acdS) is one of the most diffused. This gene is supposed to be involved in the cleaving of plant-produced ACC, the precursor of the plant stress-hormone ethylene toning down the plant response to infection. However, few reports are present on the actual role in rhizobia, one of the most investigated groups of plant-associated bacteria. In particular, still unclear is the origin and the role of acdS in symbiotic competitiveness and on the selective benefit it may confer to plant symbiotic rhizobia. Here we present a phylogenetic and functional analysis of acdS orthologs in the rhizobium model-species Sinorhizobium meliloti. Results showed that acdS orthologs present in S. meliloti pangenome have polyphyletic origin and likely spread through horizontal gene transfer, mediated by mobile genetic elements. When acdS ortholog from AK83 strain was cloned and assayed in S. meliloti 1021 (lacking acdS), no modulation of plant ethylene levels was detected, as well as no increase in fitness for nodule occupancy was found in the acdS-derivative strain compared to the parental one. Surprisingly, AcdS was shown to confer the ability to utilize formamide and some dipeptides as sole nitrogen source. Finally, acdS was shown to be negatively regulated by a putative leucine-responsive regulator (LrpL) located upstream to acdS sequence (acdR). acdS expression was induced by root exudates of both legumes and non-leguminous plants. We conclude that acdS in S. meliloti is not directly related to symbiotic interaction, but it could likely be involved in the rhizospheric colonization or in the endophytic behavior.

Studies on Plant Growth Promoting Properties of Fruit-Associated Bacteria from Elettaria cardamomum and Molecular Analysis of ACC Deaminase Gene.

Endophytic microorganisms have been reported to have diverse plant growth promoting mechanisms including phosphate solubilization, N2 fixation, production of phyto-hormones and ACC (1-aminocyclopropane-1-carboxylate) deaminase and antiphyto-pathogenic properties. Among these, ACC deaminase production is very important because of its regulatory effect on ethylene which is a stress hormone with precise role in the control of fruit development and ripening. However, distribution of these properties among various endophytic bacteria associated with fruit tissue and its genetic basis is least investigated. In the current study, 11 endophytic bacteria were isolated and identified from the fruit tissue of Elettaria cardamomum and were studied in detail for various plant growth promoting properties especially ACC deaminase activity using both culture-based and PCR-based methods. PCR-based screening identified the isolates EcB 2 (Pantoea sp.), EcB 7 (Polaromonas sp.), EcB 9 (Pseudomonas sp.), EcB 10 (Pseudomonas sp.) and EcB 11 (Ralstonia sp.) as positive for ACC deaminase. The PCR products were further subjected to sequence analysis which proved the similarity of the sequences identified in the study with ACC deaminase sequences reported from other sources. The detailed bioinformatic analysis of the sequence including homology-based modelling and molecular docking confirmed the sequences to have ACC deaminase activity. The docking of the modelled proteins was done using patch dock, and the detailed scrutiny of the protein ligand interaction revealed conservation of key amino acids like Lys51, Ser78, Tyr268 and Tyr294 which play important role in the enzyme activity. These suggest the possible regulatory effect of these isolates on fruit physiology.

Plant-Agrobacterium interaction mediated by ethylene and super-Agrobacterium conferring efficient gene transfer.

Agrobacterium tumefaciens has a unique ability to transfer genes into plant genomes. This ability has been utilized for plant genetic engineering. However, the efficiency is not sufficient for all plant species. Several studies have shown that ethylene decreased the Agrobacterium-mediated transformation frequency. Thus, A. tumefaciens with an ability to suppress ethylene evolution would increase the efficiency of Agrobacterium-mediated transformation. Some studies showed that plant growth-promoting rhizobacteria (PGPR) can reduce ethylene levels in plants through 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, which cleaves the ethylene precursor ACC into α-ketobutyrate and ammonia, resulting in reduced ethylene production. The whole genome sequence data showed that A. tumefaciens does not possess an ACC deaminase gene in its genome. Therefore, providing ACC deaminase activity to the bacteria would improve gene transfer. As expected, A. tumefaciens with ACC deaminase activity, designated as super-Agrobacterium, could suppress ethylene evolution and increase the gene transfer efficiency in several plant species. In this review, we summarize plant–Agrobacterium interactions and their applications for improving Agrobacterium-mediated genetic engineering techniques via super-Agrobacterium.