Proteomic Analysis Reveals the Positive Roles of the Plant-Growth-Promoting Rhizobacterium NSY50 in the Response of Cucumber Roots to Fusarium oxysporum f. sp. cucumerinum Inoculation.

Nanshan Du,Yinghui Yuan,Jin Sun,Sheng Shu,Bin Li,Shirong Guo,Lu Shi

doi:10.3389/fpls.2016.01859

Abstract

Plant-growth-promoting rhizobacteria (PGPR) can both improve plant growth and enhance plant resistance against a variety of environmental stresses. To investigate the mechanisms that PGPR use to protect plants under pathogenic attack, transmission electron microscopy analysis and a proteomic approach were designed to test the effects of the new potential PGPR strain Paenibacillus polymyxa NSY50 on cucumber seedling roots after they were inoculated with the destructive phytopathogen Fusarium oxysporum f. sp. cucumerinum (FOC). NSY50 could apparently mitigate the injury caused by the FOC infection and maintain the stability of cell structures. The two-dimensional electrophoresis (2-DE) approach in conjunction with MALDI-TOF/TOF analysis revealed a total of 56 proteins that were differentially expressed in response to NSY50 and/or FOC. The application of NSY50 up-regulated most of the identified proteins that were involved in carbohydrate metabolism and amino acid metabolism under normal conditions, which implied that both energy generation and the production of amino acids were enhanced, thereby ensuring an adequate supply of amino acids for the synthesis of new proteins in cucumber seedlings to promote plant growth. Inoculation with FOC inhibited most of the proteins related to carbohydrate and energy metabolism and to protein metabolism. The combined inoculation treatment (NSY50+FOC) accumulated abundant proteins involved in defense mechanisms against oxidation and detoxification as well as carbohydrate metabolism, which might play important roles in preventing pathogens from attacking. Meanwhile, western blotting was used to analyze the accumulation of enolase (ENO) and S-adenosylmethionine synthase (SAMs). NSY50 further increased the expression of ENO and SAMs under FOC stress. In addition, NSY50 adjusted the transcription levels of genes related to those proteins. Taken together, these results suggest that P. polymyxa NSY50 may promote plant growth and alleviate FOC-induced damage by improving the metabolism and activation of defense-related proteins in cucumber roots.

Highlights

Cucumber (Cucumis sativus L.) is an important and popular vegetable cash crop that is consumed worldwide
Under pathogen stress, plant biomass was significantly higher in P. polymyxa NSY50 pre-treated cucumber plants, which showed a 1.2–1.5-fold up-regulation in plant growth compared to untreated plants
The results clearly indicated that the pathogen inoculation inhibited growth in cucumber seedlings and that P. polymyxa NSY50 can release at least a portion of the stress and promote plant growth

Summary

Introduction

Cucumber (Cucumis sativus L.) is an important and popular vegetable cash crop that is consumed worldwide. Alternative methods, such as biological control agents, have been shown to be effective and have been increasingly applied in the field (Yang et al, 2010; Li et al, 2012; Lin et al, 2014; Xu et al, 2014). Among these methods, some beneficial bacteria inhabiting the plant rhizosphere, called plant growthpromoting rhizobacteria (PGPR), are directly or indirectly involved in promoting plant growth and the biological control of plant diseases (Kloepper and Metting, 1992). A variety of mechanisms have been confirmed to improve plant health and increase crop productivity for those strains, such as synthesizing different antimicrobial compounds (Tamehiro et al, 2002; Ongena et al, 2007; Chen et al, 2014), various hormones (Bottini et al, 2004; Martínez-Viveros et al, 2010; Kochar et al, 2011), increasing the availability of plant nutrients in the rhizosphere (Idriss et al, 2002; Palacios et al, 2014), and inducing systemic resistance in host plants (Niu et al, 2011; Jiang et al, 2015)

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Conclusion