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. 2016 Dec 10;17(12):2076.
doi: 10.3390/ijms17122076.

Structural Characterization of Oligochitosan Elicitor from Fusarium sambucinum and Its Elicitation of Defensive Responses in Zanthoxylum bungeanum

Peiqin Li  1 , Robert J Linhardt  2   3 , Zhimin Cao  4
Affiliations

Structural Characterization of Oligochitosan Elicitor from Fusarium sambucinum and Its Elicitation of Defensive Responses in Zanthoxylum bungeanum

Peiqin Li et al. Int J Mol Sci. .

Abstract

Oligosaccharide elicitors from pathogens have been shown to play major roles in host plant defense responses involving plant-pathogen chemoperception and interaction. In the present study, chitosan and oligochitosan were prepared from pathogen Fusarium sambucinum, and their effects on infection of Zanthoxylum bungeanum stems were investigated. Results showed that oligochitosan inhibited the infection of the pathogen, and that the oligochitosan fraction with a degree of polymerization (DP) between 5 and 6 showed the optimal effect. Oligochitosan DP5 was purified from fraction DP5-6 and was structurally characterized using electrospray ionization mass spectrometry, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. Oligochitosan DP5 showed significant inhibition against the infection of the pathogenic fungi on host plant stems. An investigation of the mechanism underlying this effect showed that oligochitosan DP5 increased the activities of defensive enzymes and accumulation of phenolics in host Z. bungeanum. These results suggest that oligochitosan from pathogenic fungi can mediate the infection of host plants with a pathogen by acting as an elicitor that triggers the defense system of a plant. This information will be valuable for further exploration of the interactions between the pathogen F. sambucinum and host plant Z. bungeanum.

Keywords: Fusarium sambucinum; Zanthoxylum bungeanum; defensive response; fungal oligochitosan elicitor; plant–pathogen interaction; structural characterization.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Effects of chitosan and oligochitosan elicitors from pathogen Fusarium sambucinum on infection of Zanthoxylum bungeanum stems. Different letters (a–i) indicate significant differences at a level of p < 0.05 of infection incidence among the treatments. CCH, crude chitosan; DCH, deacetyated chitosan; TOCH, total oligochitosan; DP, degree of polymerization.
Figure 2
Figure 2
Positive ion electrospray ionization mass spectrometry (ESI-MS) spectrum (A); and Fourier transform infrared (FT-IR) spectrum (B) of oligochitosan DP5. The typical ion peaks for oligochitosan are indicated by blue and red star symbols in the ESI-MS spectrum. Blue stars represent the fragment ions 824.33, 663.26, 502.25 and 341.27 and 180.03 with one glucosamine residue decrease successively. Red stars represent the fragment ions 806.49, 645.28, 484.23, 323.17, and 162.07 with one glucosamine residue decrease successively. The important IR absorbances for oligochitosan are also shown in the FT-IR spectrum (red arrows).
Figure 3
Figure 3
The spectra of: 1H-NMR (A); 13C-NMR (B); and DEPT-135 (C) of oligochitosan DP5. DP5 was dissolved in D2O at a concentration of 10 mg/mL. NMR, nuclear magnetic resonance; DEPT-135, distortionless enhancement by polarization transfer.
Figure 3
Figure 3
The spectra of: 1H-NMR (A); 13C-NMR (B); and DEPT-135 (C) of oligochitosan DP5. DP5 was dissolved in D2O at a concentration of 10 mg/mL. NMR, nuclear magnetic resonance; DEPT-135, distortionless enhancement by polarization transfer.
Figure 4
Figure 4
Two-dimensional nuclear magnetic resonance spectra of oligochitosan DP5: 1H-1H COSY (A); ROESY (B); and 1H-13C HSQC (C). Correlation peaks are marked on the spectra. COSY, correlation spectroscopy; ROESY, rotating frame nuclear Overhauser effect spectroscopy (NOESY); HSQC, heteronuclear single-quantum correlation spectroscopy.
Figure 4
Figure 4
Two-dimensional nuclear magnetic resonance spectra of oligochitosan DP5: 1H-1H COSY (A); ROESY (B); and 1H-13C HSQC (C). Correlation peaks are marked on the spectra. COSY, correlation spectroscopy; ROESY, rotating frame nuclear Overhauser effect spectroscopy (NOESY); HSQC, heteronuclear single-quantum correlation spectroscopy.
Figure 5
Figure 5
The structure of oligochitosan DP5, which is composed of five glucosamines.
Figure 6
Figure 6
Inhibitory effects of oligochitosan DP5 on Fusarium sambucinum infection of Zanthoxylum bungeanum stems. Different letters (a–d) indicate significant differences at the level of p < 0.05 in the incidence of infection with various DP5 treatments. DP5–0.01, DP5–0.05, and DP5–0.1 indicate DP5 concentrations of 0.01, 0.05, and 0.1 mg/mL, respectively.
Figure 7
Figure 7
Effects of oligochitosan DP5 on the activities of defensive enzymes: phenylalanine ammonia lyase (PAL) (A); polyphenol oxidase (PPO) (B); peroxidase (POD) (C); and chitinase (CHI) (D) in Zanthoxylum bungeanum. The error bars represent standard deviations of the means from three independent samples. FW means fresh weight of plant material.
Figure 8
Figure 8
Effect of oligochitosan DP5 on the accumulation of total phenolics in Zanthoxylum bungeanum. Error bars represent standard deviations of the means from three independent samples. FW means fresh weight of plant material. GAE means Gallic acid equivalent.
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