Inoculation of Soil with Plant Growth Promoting Bacteria Producing 1-Aminocyclopropane-1-Carboxylate Deaminase or Expression of the Corresponding acdS Gene in Transgenic Plants Increases Salinity Tolerance in Camelina sativa.

Zohreh Heydarian,Dwayne D Hegedus,Bernard R Glick,Margaret Gruber,Min Yu,Rong Zhou

doi:10.3389/fmicb.2016.01966

Abstract

Camelina sativa (camelina) is an oilseed crop touted for use on marginal lands; however, it is no more tolerant of soil salinity than traditional crops, such as canola. Plant growth-promoting bacteria (PGPB) that produce 1-aminocyclopropane-1-carboxylate deaminase (ACC deaminase) facilitate plant growth in the presence of abiotic stresses by reducing stress ethylene. Rhizospheric and endophytic PGPB and the corresponding acdS- mutants of the latter were examined for their ability to enhance tolerance to salt in camelina. Stimulation of growth and tolerance to salt was correlated with ACC deaminase production. Inoculation of soil with wild-type PGPB led to increased shoot length in the absence of salt, and increased seed production by approximately 30–50% under moderately saline conditions. The effect of ACC deaminase was further examined in transgenic camelina expressing a bacterial gene encoding ACC deaminase (acdS) under the regulation of the CaMV 35S promoter or the root-specific rolD promoter. Lines expressing acdS, in particular those using the rolD promoter, showed less decline in root length and weight, increased seed production, better seed quality and higher levels of seed oil production under salt stress. This study clearly demonstrates the potential benefit of using either PGPB that produce ACC deaminase or transgenic plants expressing the acdS gene under the control of a root-specific promoter to facilitate plant growth, seed production and seed quality on land that is not normally suitable for the majority of crops due to high salt content.

Highlights

Salinity stress is a worldwide agricultural problem that negatively affects plant growth and production
Effect of the Plant growth-promoting bacteria (PGPB) on Shoot Length and Weight Twenty days after sowing, inoculation with UW4 or YsS6 did not have any significant effect on shoot length, but plants grown in soil inoculated with 8R6 or the 8R6M ACC deaminase (acdS)- mutant had slightly longer shoots relative to the control (Figure 1). 27 days after sowing, plants grown in soil inoculated with all PGPB, except YsS6M, showed significantly increased shoot length in the absence of salt, while 41 days after sowing, plants grown in soil inoculated with any of the three wildtype PGPB had longer shoots under the no salt condition
Plants grown in soil inoculated with UW4 had reduced shoot fresh weight in the control and 15 dSm−1 salt treatments, while inoculation of soil with the two endophytic PGPB did not affect shoot fresh weight significantly in either the control or salt treatments

Summary

Introduction

Salinity stress is a worldwide agricultural problem that negatively affects plant growth and production. Global warming is expected to increase soil salinity due to higher evaporation and lower precipitation Irrigation from both ground and surface water sources increases soil salinity over time as dissolved minerals accumulate in the soil. Camelina sativa (camelina), a member of the Brassicaceae family and a close relative of the model plant Arabidopsis thaliana and the oilseed Brassica crops, such as canola and Indian mustard, was grown extensively in medieval Europe for food and fuel. Renewed interest in this ancient crop stems from demand for species that can diversify annual crop rotation portfolios, with a lower environmental footprint and with potential to produce high value secondary products. Growth, seed yield and oil content studies showed that camelina does not perform as well as canola when grown under conditions that simulate prairie saline soils; in particular camelina seed yield is much lower under saline conditions (Steppuhn et al, 2010)

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