Abstract
Cucumber green mottle mosaic virus (CGMMV) is an important viral pathogen on cucurbit plants worldwide, which can cause severe fruit decay symptoms on infected watermelon (usually called “watermelon blood flesh”). However, the molecular mechanism of this disease has not been well understood. In this study, we employed the isobaric tags for relative and absolute quantitation (iTRAQ) technique to analyze the proteomic profiles of watermelon fruits in response to CGMMV infection. A total of 595 differentially accumulated proteins (DAPs) were identified, of which 404 were upregulated and 191 were downregulated. Functional annotation analysis showed that these DAPs were mainly involved in photosynthesis, carbohydrate metabolism, secondary metabolite biosynthesis, plant–pathogen interaction, and protein synthesis and turnover. The accumulation levels of several proteins related to chlorophyll metabolism, pyruvate metabolism, TCA cycle, heat shock proteins, thioredoxins, ribosomal proteins, translation initiation factors, and elongation factors were strongly affected by CGMMV infection. Furthermore, a correlation analysis was performed between CGMMV-responsive proteome and transcriptome data of watermelon fruits obtained in our previous study, which could contribute to comprehensively elucidating the molecular mechanism of “watermelon blood flesh”. To confirm the iTRAQ-based proteome data, the corresponding transcripts of ten DAPs were validated by determining their abundance via quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR). These results could provide a scientific basis for in-depth understanding of the pathogenic mechanisms underlying CGMMV-induced “watermelon blood flesh”, and lay the foundation for further functional exploration and verification of related genes and proteins.
Highlights
During the infection–defense interaction between viruses and plants, host symptoms are the result of huge intricate disturbance and change of cellular processes [1,2,3,4]
Cucumber green mottle mosaic virus (CGMMV) infection of flesh from inoculated plants at two months after inoculation was confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) and dot enzyme-linked immunosorbent assay (Dot-ELISA) using CGMMV-specific primers and CGMMV coat protein monoclonal antibody (Figure 1c,d)
Among differentially accumulated proteins (DAPs) involved in photosynthesis, ATP synthase, red chlorophyll catabolite reductase (RCCR) and phytoene synthase (Psy) significantly accumulated to higher levels after CGMMV infection
Summary
During the infection–defense interaction between viruses and plants, host symptoms are the result of huge intricate disturbance and change of cellular processes [1,2,3,4]. A few years ago, pathogenesis studies were very rare on how virus infection causes pathological changes in plants based on differential expression analysis of protein level. Isobaric tags for relative and absolute quantitation (iTRAQ) technology is a quantitative proteomics technique using isotope labeling that was established in 2004 [14]. This technique has been widely applied in proteome sequencing studies with high accuracy and reproducibility in recent years. CGMMV infection usually results in severe disease symptoms on watermelon plants, and especially, it causes a fruit decay called “watermelon blood flesh”. We have employed high-throughput sequencing technology to analyze transcriptome differences between CGMMV-inoculated and mock-inoculated watermelon fruits [30]. To the best of our knowledge, this is the first report on the proteomic profiles of watermelon fruits in response to CGMMV infection by the iTRAQ technique
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