Comparative proteomic analysis reveals novel insights into the interaction between rice and Xanthomonas oryzae pv. oryzae

Abstract

Background: Bacterial blight, which is caused by Xanthomonas oryzae pv. oryzae (Xoo), is a devastating rice disease worldwide. Rice introgression line H471, derived from the recurrent parent Huang-Hua-Zhan (HHZ) and the donor parent PSBRC28, exhibits broad-spectrum resistance to Xoo, including to the highly virulent Xoo strain PXO99^A, whereas its parents are susceptible to PXO99^A. To characterize the responses to Xoo, we compared the proteome profiles of the host and pathogen in the incompatible interaction (H471 inoculated with PXO99^A) and the compatible interaction (HHZ inoculated with PXO99^A).

Results: In this study, a total of 374 rice differentially abundant proteins (DAPs) and 117 Xoo DAPs were detected in the comparison between H471 + PXO99^A and HHZ + PXO99^A. Most of the Xoo DAPs related to pathogen virulence, including the outer member proteins, type III secretion system proteins, TonB-dependent receptors, and transcription activator-like effectors, were less abundant in the incompatible interaction than in the compatible interaction. The rice DAPs were mainly involved in secondary metabolic processes, including phenylalanine metabolism and the biosynthesis of flavonoids and phenylpropanoids. Additionally, some DAPs involved in the phenolic phytoalexin and salicylic acid (SA) biosynthetic pathways accumulated much more in H471 than in HHZ after the inoculation with PXO99^A, suggesting that phytoalexin and SA productions were induced faster in H471 than in HHZ. Further analyses revealed that the SA content increased much more rapidly in H471 than in HHZ after the inoculation, suggesting that the SA signaling pathway was activated faster in the incompatible interaction than in the compatible interaction.

Conclusions: Overall, our results indicate that during an incompatible interaction between H471 and PXO99^A, rice plants prevent pathogen invasion and also initiate multi-component defense responses that inhibit disease development.

Keywords: Compatible interaction; Incompatible interaction; Quantitative proteome; Rice; Xanthomonas oryzae pv. oryzae.

Fig. 1

Phenotypic reactions of rice introgression line H471 and its recurrent parent Huang-Hua-Zhan (HHZ) to an infection by Xanthomonas oryzae pv. oryzae strain PXO99^A. a Phenotypes of HHZ and H471 plants infected with Xoo strain PXO99^A. Photographs were taken 14 days after inoculation. b Lesion lengths on H471 and HHZ plants infected with PXO99^A at 14 dpi. Data are presented as the mean of nine independent plants for each line; vertical bars indicate the standard deviation. *** significant differences between HHZ and H471 at p < 0.001 based on Student’s t-test. c Growth curves of PXO99^A in H471 and HHZ. CFU indicates colony-forming units. d Transmission electron microscopy analysis of H471 and HHZ mesophyll cells after the inoculation with PXO99^A. N, nucleus; C, chloroplast; S, starch; DC, damaged chloroplast; DN, damaged nucleus

Fig. 2

Differentially abundant proteins (DAPs) identified by pairwise comparisons between H471 and HHZ at two time-points after the inoculation with PXO99^A. Venn diagrams of rice DAPs (a) and Xanthomonas oryzae pv. oryzae (Xoo) DAPs (b) between H471 and HHZ at two time-points. The individual and overlapping areas in the Venn diagrams represent the number of specific and common DAPs. Heat map of rice DAPs (c) and Xoo DAPs (d) between H471 and HHZ at two time-points after the inoculation with PXO99^A. Each cell reflects the mean value of the normalized accumulation of one DAP in three biological replicates per sample. Rice DAPs are divided into five main clusters, namely G-I to G-V

Fig. 3

Abundances of OsbZIP23, OsCDPK13, OsMKK4, and OsMPK6 in HHZ and H471 after the inoculation with PXO99^A. (a) and (b) represent the protein abundances in HHZ and H471, respectively, as determined in a western blot analysis. The relative OsbZIP23, OsCDPK13, OsMKK4, and OsMPK6 abundances were analyzed with Image J. Full-length blot images were presented in Additional file 12. The experiments were repeated three times, with similar results

Fig. 4

Patterns of the Xanthomonas oryzae pv. oryzae (Xoo) and rice differentially abundant proteins assigned to six main categories putatively related to incompatible and compatible interactions. a Outer membrane proteins (Omp) and TonB-dependent receptors (TonB). b Virulence-related proteins in Xoo. c Kinases and phosphatases. d Transcription factors. e Phytohormone-related proteins. f Phytoalexin-related proteins. g Defense response proteins. Red and blue represent Xoo and rice proteins, respectively

Fig. 5

Free salicylic acid contents of HHZ and H471 plants inoculated with PXO99^A. Data are presented as the mean (two replicates) ± standard deviation. NS p > 0.05, * p < 0.05, and *** p < 0.001

Fig. 6

Putative defense pathway underlying the incompatible interaction between H471 and PXO99^A. Red indicates the proteins were more abundant in H471 than in HHZ. White indicates the proteins were undetectable in this dataset. PEP: phosphoenolpyruvate; E4P: erythrose 4-phosphate; CM: chorismate mutase; ICS: isochorismate synthase; PAL: phenylalanine ammonia-lyase; 4CL: 4-coumarate CoA ligase; COMT: caffeoyl-CoA O-methyltransferase; OMT: O-methyltransferase; CHI: chalcone-flavonone isomerase. Scaled abundance values are presented in the heat map legend. Each row in the heat map corresponds to one protein. The four boxes in each row (left to right) correspond respectively to protein abundances after the inoculation with PXO99^A in HHZ at 2 and 3 dpi and in H471 at 2 and 3 dpi