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

Yupei Liu,Hongming Tan,Renduo Zhang,Lixiang Cao

doi:10.1186/s12934-017-0831-5

Abstract

BackgroundMost 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).ResultsResults 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.ConclusionsThe 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.

Highlights

Most endophytic bacteria in consortia, which provide robust and broad metabolic capacity, are attractive for applications in plant metabolic engineering
Most of natural microbes exist in consortia to provide robust and broad metabolic capacity and these traits are attractive for applications in the plant metabolic engineering [9]
Isolation of endophytic bacteria and construction of strains displaying ACC deaminase After incubated at 26 °C for 4 days, pink colonies grown on the sprout samples were picked and further purified on the Eosin-Methylene Blue (EMB) medium with 1.5% agar

Summary

Introduction

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. Most of natural microbes exist in consortia to provide robust and broad metabolic capacity and these traits are attractive for applications in the plant metabolic engineering [9]. The expression of ACC deaminases by symbiotic bacteria can alleviate the ethylene-mediated negative impact on plants [11, 12]. The ACC deaminase can be used as a good model to study the effects of symbiotic bacterial enzymes on the outcome of metabolic engineering in plants

Objectives

Methods

Results

Discussion

Conclusion