Bacillus licheniformis SA03 Confers Increased Saline-Alkaline Tolerance in Chrysanthemum Plants by Induction of Abscisic Acid Accumulation.

Cheng Zhou,Lin Zhu,Feiyue Li,Xin Xiao,Zhongyou Ma,Jianfei Wang,Yue Xie

doi:10.3389/fpls.2017.01143

Abstract

Soil saline-alkalization is a major abiotic stress that leads to low iron (Fe) availability and high toxicity of sodium ions (Na+) for plants. It has recently been shown that plant growth promoting rhizobacteria (PGPR) can enhance the ability of plants to tolerate multiple abiotic stresses such as drought, salinity, and nutrient deficiency. However, the possible involvement of PGPR in improving saline–alkaline tolerance of plants and the underlying mechanisms remain largely unknown. In this study, we investigated the effects of Bacillus licheniformis (strain SA03) on the growth of Chrysanthemum plants under saline–alkaline conditions. Our results revealed that inoculation with SA03 alleviated saline–alkaline stress in plants with increased survival rates, photosynthesis and biomass. The inoculated plants accumulated more Fe and lower Na+ concentrations under saline–alkaline stress compared with the non-inoculated plants. RNA-Sequencing analyses further revealed that SA03 significantly activated abiotic stress- and Fe acquisition-related pathways in the stress-treated plants. However, SA03 failed to increase saline–alkaline tolerance in plants when cellular abscisic acid (ABA) and nitric oxide (NO) synthesis were inhibited by treatment with fluridone (FLU) and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), respectively. Importantly, we also found that NO acted downstream of SA03-induced ABA to activate a series of adaptive responses in host plants under saline–alkaline stress. These findings demonstrated the potential roles of B. licheniformis SA03 in enhancing saline–alkaline tolerance of plants and highlighted the intricate integration of microbial signaling in regulating cellular Fe and Na+ accumulation.

Highlights

Plants as sessile organisms cannot escape from negative effects imposed by detrimental environments such as high salinity, drought, freezing, high temperature, and flooding
To examine the effects of SA03-inoculation on the growth of Chrysanthemum plants under saline–alkaline stress, about 3-month-old plants were inoculated with this bacteria strain
We reported here for the first time that Chrysanthemum plants inoculated with B. licheniformis SA03 were greater resistant to saline–alkaline conditions, as evidenced by lower biomass loss and higher survival rates

Summary

Introduction

Plants as sessile organisms cannot escape from negative effects imposed by detrimental environments such as high salinity, drought, freezing, high temperature, and flooding. Soil salinity has increasingly become one of major abiotic stresses that constraint plant growth worldwide (Frommer et al, 1999). Soil salinity and alkalinity often occurs simultaneously due to Bacillus licheniformis Increases Saline–Alkaline Tolerance in Plants the complexity of soils (Zhang et al, 2015). Half of the saline soils in earth’s crust contain NaHCO3 and Na2CO3, which are the main factors that contribute to soil alkalinity (Yang et al, 2009). Excess Na+ and high pH value in saline–alkaline soils cause considerable damages to plant growth and development, whereas most plant species are more susceptible to high pH soils (more than 8.0) than saline soils (Tang et al, 2014; Li et al, 2016). It is an urgent need to develop effective strategies to enhance the ability of plants to tolerate saline–alkaline conditions

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