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Surface display of ACC deaminase on endophytic Enterobacteriaceae strains to increase saline resistance of host rice sprouts by regulating plant ethylene synthesis.

ABSTRACT: Most endophytic bacteria in consortia, which provide robust and broad metabolic capacity, are attractive for applications in plant metabolic engineering. The aim of this study was to investigate the effects of engineered endophytic bacterial strains on rice sprout ethylene level and growth under saline stress. A protocol was developed to synthesize engineered strains by expressing bacterial 1-aminocyclopropane-1-carboxylate (ACC) deaminase gene on cells of endophytic Enterobacter sp. E5 and Kosakonia sp. S1 (denoted as E5P and S1P, respectively).Results showed that ACC deaminase activities of the engineered strains E5P and S1P were significantly higher than those of the wild strains E5 and S1. About 32-41% deaminase was expressed on the surface of the engineered strains. Compared with the controls without inoculation, inoculation with the wild and engineered strains increased the deaminase activities of sprouts. Inoculation with the engineered strains increased 15-21% more deaminase activities of sprouts than with the wild strains, and reduced the ethylene concentrations of sprouts more significantly than with wild strains (P < 0.05). Inoculation with the wild and engineered strains promoted the growth of sprouts, while the promoting effects were more profound with the engineered strains than with the wild strains. The engineered strains improved saline resistance of sprouts under salt concentrations from 10 to 25 g L-1. The engineered strains promoted longer roots and shoots than the wild strains under the salt stresses, indicating that the ACC deaminases on the endophytic bacterial cells could result in plant-produced ACC degradation and inhibit plant ethylene formation.The protocols of expressing enzymes on endophytic bacterial cells showed greater potentials than those of plant over-expressed enzymes to increase the efficiency of plant metabolic pathways.

SUBMITTER: Liu Y

PROVIDER: S-EPMC5704625 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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Surface display of ACC deaminase on endophytic Enterobacteriaceae strains to increase saline resistance of host rice sprouts by regulating plant ethylene synthesis.

Liu Yupei Y Cao Lixiang L Tan Hongming H Zhang Renduo R

Microbial cell factories 20171128 1

<h4>Background</h4>Most endophytic bacteria in consortia, which provide robust and broad metabolic capacity, are attractive for applications in plant metabolic engineering. The aim of this study was to investigate the effects of engineered endophytic bacterial strains on rice sprout ethylene level and growth under saline stress. A protocol was developed to synthesize engineered strains by expressing bacterial 1-aminocyclopropane-1-carboxylate (ACC) deaminase gene on cells of endophytic Enterobac ...[more]

PMID: 29183329

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Project description:1-aminocyclopropane-1-carboxylate deaminase (ACCD), a pyridoxal phosphate-dependent enzyme, is widespread in diverse bacterial and fungal species. Owing to ACCD activity, certain plant associated bacteria help plant to grow under biotic and abiotic stresses by decreasing the level of "stress ethylene" which is inhibitory to plant growth. ACCD breaks down ACC, an immediate precursor of ethylene, to ammonia and α-ketobutyrate, which can be further metabolized by bacteria for their growth. ACC deaminase is an inducible enzyme whose synthesis is induced in the presence of its substrate ACC. This enzyme encoded by gene AcdS is under tight regulation and regulated differentially under different environmental conditions. Regulatory elements of gene AcdS are comprised of the regulatory gene encoding LRP protein and other regulatory elements which are activated differentially under aerobic and anaerobic conditions. The role of some additional regulatory genes such as AcdB or LysR may also be required for expression of AcdS. Phylogenetic analysis of AcdS has revealed that distribution of this gene among different bacteria might have resulted from vertical gene transfer with occasional horizontal gene transfer (HGT). Application of bacterial AcdS gene has been extended by developing transgenic plants with ACCD gene which showed increased tolerance to biotic and abiotic stresses in plants. Moreover, distribution of ACCD gene or its homolog's in a wide range of species belonging to all three domains indicate an alternative role of ACCD in the physiology of an organism. Therefore, this review is an attempt to explore current knowledge of bacterial ACC deaminase mediated physiological effects in plants, mode of enzyme action, genetics, distribution among different species, ecological role of ACCD and, future research avenues to develop transgenic plants expressing foreign AcdS gene to cope with biotic and abiotic stressors. Systemic identification of regulatory circuits would be highly valuable to express the gene under diverse environmental conditions.

Project description:IntroductionDrought has become more prevalent due to dramatic climate change worldwide. Consequently, the most compatible fungal communities collaborate to boost plant development and ecophysiological responses under environmental constraints. However, little is known about the specific interactions between non-host plants and endophytic fungal symbionts that produce growth-promoting and stress-alleviating hormones during water deficits.MethodsThe current research was rationalized and aimed at exploring the influence of the newly isolated, drought-resistant, ACC deaminase enzyme-producing endophytic fungi Trichoderma gamsii (TP), Fusarium proliferatum (TR), and its consortium (TP+TR) from a xerophytic plant Carthamus oxycantha L. on Moringa oleifera L. grown under water deficit induced by PEG-8000 (8% osmoticum solution).ResultsThe current findings revealed that the co-inoculation promoted a significant enhancement in growth traits such as dry weight (217%), fresh weight (123%), root length (65%), shoot length (53%), carotenoids (87%), and chlorophyll content (76%) in comparison to control plants under water deficit. Total soluble sugars (0.56%), proteins (132%), lipids (43%), flavonoids (52%), phenols (34%), proline (55%), GA3 (86%), IAA (35%), AsA (170%), SA (87%), were also induced, while H2O2 (-45%), ABA (-60%) and ACC level (-77%) was decreased by co-inoculation of TP and TR in M. oleifera plants, compared with the non-inoculated plants under water deficit. The co-inoculum (TP+TR) also induced the antioxidant potential and enzyme activities POX (325%), CAT activity (166%), and AsA (21%), along with a lesser decrease (-2%) in water potential in M. oleifera plants with co-inoculation under water deficit compared with non-inoculated control. The molecular analysis for gene expression unraveled the reduced expression of ethylene biosynthesis and signaling-related genes up to an optimal level, with an induction of antioxidant enzymatic genes by endophytic co-inoculation in M. oleifera plants under water deficit, suggesting their role in drought stress tolerance as an essential regulatory function.ConclusionThe finding may alert scientists to consider the impacts of optimal reduction of ethylene and induction of antioxidant potential on drought stress tolerance in M. oleifera. Hence, the present study supports the use of compatible endophytic fungi to build a bipartite mutualistic symbiosis in M. oleifera non-host plants to mitigate the negative impacts of water scarcity in arid regions throughout the world.

Project description:BackgroundEndophytic bacteria reside inside healthy plant tissues and provide several benefits to their host, and help them to tolerate various stresses. Aminocyclopropane-1-carboxylate deaminase (ACCD) production is one of the mechanisms by which these bacteria help the plant to survive under ethylene stress.ObjectivesThe main focus of this study was to isolate endophytic bacteria and effectively screen them for ACCD production. The selected isolate was identified and assessed for plant growth-promoting potential under pot conditions.Materials and methodsEndophytic bacteria were isolated from root nodules of Pisum sativum plants, grown in northern India (Haryana state). ACCD activity was initially screened on DF minimal salt medium with ACC as a sole nitrogen source. To narrow down the number of the isolates, another screening method was adopted using a modified medium containing indicator dyes along with ACC. The strain producing ACCD as well as a significant amount of Indole 3 acetic acid (IAA) was identified using 16S rDNA gene sequencing and amplification of acdS gene. Its ability to promote plant growth was evaluated under pot culture conditions.ResultsTwenty-six endophytic bacteria were isolated from nodules of P. sativum plants. Sixteen isolates showed growth on DF minimal salts medium supplemented with ACC along with negative control. On the modified medium containing indicator dyes, two isolates, PJN13 and PJN17, showed zones of the color gradient. The ACC deaminase activity was further confirmed by enzymatic assay. The strains PJN13 and PJN17 produced 160 and 130 µM of ?-ketobutyrate m.g-1 protein h-1, respectively. The IAA production in the strain PJN13 (79.04 ± 0.78 µg.mL -1) was significantly more than that in the strain PJN17 (38.36 ± 1.89 µg.mL-1). It could enhance pea plant growth parameters, including root and shoot length and fresh and dry weight from 1 to 4 times compare to the control (untreated pea plants) under pot conditions. The results of 16S rDNA amplification and sequencing showed that PJN13 has maximum similarity to Bacillus mojavensis, and the sequence submitted to GenBank under accession number MH298523. Also, a band about 800 bp was amplified for the acdS gene.ConclusionsThough Bacillus is known as a predominant non-rhizobial endophytic genus, however in the present study, a B. mojavensis Bacillus mojavensis PRN2 (MH298523) was reported for the first time as an endophyte from the nodules of pea plants. The isolated strain possesses ACC deaminase activity along with IAA production capability, and high potentials as PGPE (Plant growth-promoting endophyte) for plant growth, so it has potential to be used as biofertilizers in pea fields.

Dataset Information

Surface display of ACC deaminase on endophytic Enterobacteriaceae strains to increase saline resistance of host rice sprouts by regulating plant ethylene synthesis.

Publications

Surface display of ACC deaminase on endophytic Enterobacteriaceae strains to increase saline resistance of host rice sprouts by regulating plant ethylene synthesis.

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