A Proteomic Approach to Lipo-Chitooligosaccharide and Thuricin 17 Effects on Soybean GerminationUnstressed and Salt Stress.

Sowmyalakshmi Subramanian,Alfred Souleimanov,Emily Ricci,Donald L Smith,Belay T Ayele

doi:10.1371/journal.pone.0160660

Abstract

Salt stress is an important abiotic stressor affecting crop growth and productivity. Of the 20 percent of the terrestrial earth’s surface available as agricultural land, 50 percent is estimated by the United Nations Environment Program to be salinized to the level that crops growing on it will be salt-stressed. Increased soil salinity has profound effects on seed germination and germinating seedlings as they are frequently confronted with much higher salinities than vigorously growing plants, because germination usually occurs in surface soils, the site of greatest soluble salt accumulation. The growth of soybean exposed to 40 mM NaCl is negatively affected, while an exposure to 80 mM NaCl is often lethal. When treated with the bacterial signal compounds lipo-chitooligosaccharide (LCO) and thuricin 17 (Th17), soybean seeds (variety Absolute RR) responded positively at salt stress of up to 150 mM NaCl. Shotgun proteomics of unstressed and 100 mM NaCl stressed seeds (48 h) in combination with the LCO and Th17 revealed many known, predicted, hypothetical and unknown proteins. In all, carbon, nitrogen and energy metabolic pathways were affected under both unstressed and salt stressed conditions when treated with signals. PEP carboxylase, Rubisco oxygenase large subunit, pyruvate kinase, and isocitrate lyase were some of the noteworthy proteins enhanced by the signals, along with antioxidant glutathione-S-transferase and other stress related proteins. These findings suggest that the germinating seeds alter their proteome based on bacterial signals and on stress, the specificity of this response plays a crucial role in organ maturation and transition from one stage to another in the plants' life cycle; understanding this response is of fundamental importance in agriculture and, as a result, global food security. The mass spectrometry proteomics data have been deposited to the ProteomeXchange with identifier PXD004106.

Highlights

Soil salinization, one of the most serious agricultural limitations worldwide, is exacerbated by a number of factors including climate, the inherent salt content of the soil, topography, underlying geology and hydrology [1]
Bacterial signal compounds LCO and thuricin 17 (Th17) on soybean seed germination was evaluated in this study under optimal and salt stress conditions
LCO 10-6 M and Th17 10-9 M helped germinating soybean seeds overcome salinity stress and did this most effectively at 100 mM NaCl (Figs 1 and 2), when measured at 48 h after the onset of germination, seeds continued to germinated at higher levels of stress

Summary

Introduction

One of the most serious agricultural limitations worldwide, is exacerbated by a number of factors including climate (degree of water deficit), the inherent salt content of the soil, topography, underlying geology and hydrology [1]. In Canada, dry-land salinity is a significant agronomic problem across the prairies [6] where approximately 1 million ha is affected by moderate to severe topsoil salinity [1]. A government of Alberta report suggests the dominant salts in prairie saline seeps are calcium (Ca), magnesium (Mg), sodium (Na) cations and sulfate (SO4) anions, and that the impact of moderate to severe soil salinity [electrical conductivity of a saturated paste extract (ECe) of 8 to 16 dS m-1 and ECe > 16 dS m-1, respectively] is apparent for almost all crops produced under dry-land agriculture conditions in this region, with yield reductions up to 50% in cereals and oilseeds crops [1]. The presence of saline soils substantially alters plant metabolic processes [12]

Objectives

Methods

Results

Discussion

Conclusion