Induced Resistance Mechanism of Novel Curcumin Analogs Bearing a Quinazoline Moiety to Plant Virus

Abstract

Plant immune activators can protect crops from plant virus pathogens by activating intrinsic immune mechanisms in plants and are widely used in agricultural production. In our previous work, we found that curcumin analogs exhibit excellent biological activity against plant viruses, especially protective activity. Inspired by these results, the active substructure of pentadienone and quinazoline were spliced to obtain curcumin analogs as potential exogenously induced resistant molecule. Bioassay results showed that compound A13 exhibited excellent protective activity for tobacco to against Tobacco mosaic virus (TMV) at 500 μg/mL, with a value of 70.4 ± 2.6% compared with control treatments, which was better than that of the plant immune activator chitosan oligosaccharide (49.0 ± 5.9%). The protective activity is due to compound A13 inducing tobacco resistance to TMV, which was related to defense-related enzymes, defense-related genes, and photosynthesis. This was confirmed by the up-regulated expression of proteins that mediate stress responses and oxidative phosphorylation.

Keywords: curcumin analogs; plant induced resistance; protective activity; quinazoline moiety; tobacco mosaic virus.

Figure 1

Design of the target compounds. The yellow circle represents the modifiable structure part of curcumin, the blue circles represent the structure part of pentadienone, and the green circles represent the structure part of quinazolinone.

Figure 2

The effect of compound A13 on CAT (A), SOD (B), and POD (C) activity in tobacco leaves. Bars indicate the mean of three replicates with the standard deviations. Different letters on the bars indicate statistically significant differences in average values by one-way ANOVA (p < 0.05).

Figure 3

The effects of compound A13 on the Ca (A), Cb (B), chlorophyll a/b (C), and Ct (D) content in tobacco leaves. Bars indicate the mean of three replicates with the standard deviations. Different letters on the bars indicate statistically significant differences in average values by one-way ANOVA (p < 0.05).

Figure 4

The expression of the defense-related genes was evaluated by RT-qPCR. The relative expression of the defense-related genes, including ICS1, EDS1, SOD, CAT1, PAL4, PR1, and NPR1, was highly up-regulated by the A13 + TMV treatment on day 3. Bars indicate the mean of three replicates with the standard deviations. Different letters on the bars indicate statistically significant differences in average values by one-way ANOVA (p < 0.05).

Figure 5

The changed in the proteome distribution between the control (CK + TMV) and treatment (A13 + TMV) groups, the diagram shows both unique and shared proteins. Blue indicates DEPs were identified in the control, orange indicates DEPs were identified in the treatment, and green indicates DEPs were identified in both treatment groups.

Figure 6

The numbers of identified proteins showing up-regulation and down-regulation in the control and treatment groups. The red spots represent up-regulate proteins, the blue dots down-regulated proteins, and the grey spots represent unchanged proteins in both treatment groups. The Log₂ Ratio indicates that the ratio between the treatment groups and the control groups takes a natural logarithm. The longitudinal coordinates indicate the magnitude of differences in the protein level. Fold change > 2, p < 0.05.

Figure 7

Cellular components, biological processes, and molecular functions involving DEPs in A13 + TMV versus CK + TMV.

Figure 8

A KEGG map of the Oxidative phosphorylation pathway of DEPs in A13 + TMV versus CK + TMV. The boxes with red frames correspond to the up-regulation of DEPs in the A13 + TMV sample. The boxes with green frames correspond to the down-regulation of DEPs in the A13 + TMV sample.