Abstract
Powdery mildew (PM) is considered a major cause of yield losses and reduced quality in cucumber worldwide, but the molecular basis of PM resistance remains poorly understood. A segment substitution line, namely, SSL508-28, was developed with dominant PM resistance in the genetic background of PM-susceptible cucumber inbred line D8. The substituted segment contains 860 genes. An iTRAQ-based comparative proteomic technology was used to map the proteomes of PM-inoculated and untreated (control) D8 and SSL508-28. The number of differentially regulated proteins (DRPs) in SSL508-28 was almost three times higher than that in D8. Fourteen DRPs were located in the substituted segment interval. Comparative gene expression analysis revealed that nodulin-related protein 1 (NRP1) may be a good candidate for PM resistance. Gene Ontology enrichment analysis showed that DRPs functioning in tetrapyrrole biosynthetic process, sulfur metabolic process and cell redox homeostasis were specifically enriched in the resistant line SSL508-28. DRPs categorized in the KEGG term photosynthesis increased in both lines upon PM infection, suggesting that the strategies used by cucumber may be different from those used by other crops to react to PM attacks at the initial stage. The measurement of hydrogen peroxide and superoxide anion production and net photosynthetic rate were consistent with the changes in protein abundance, suggesting that the proteomic results were reliable. There was a poor correlation between DRPs measured by iTRAQ and the corresponding gene expression changes measured by RNA-seq with the same experimental design. Taken together, these findings improve the understanding of the molecular mechanisms underlying the response of cucumber to PM infection.
Highlights
Cucumber (Cucumis sativus L., 2n = 2x = 14) is an important vegetable crop worldwide
Powdery mildew (PM) resistance phenotype To understand the phenotypic difference between the resistant and susceptible lines, we observed the extent of PM growth on the leaf surface by scanning electron microscopy (SEM)
Inventory of leaf proteins identified by iTRAQ To elucidate the host defense mechanisms underlying the difference in resistance between the two genotypes upon PM infection, we applied an iTRAQ proteomic technology to leaves of seedlings harvested 48 h after PM inoculation
Summary
Cucumber (Cucumis sativus L., 2n = 2x = 14) is an important vegetable crop worldwide. Powdery mildew (PM) is a destructive fungal disease that is globally distributed and that affects a wide range of agricultural and horticultural crops, including cucumber[1]. Podosphaera xanthii has been identified as the main cause of PM on cucumber[2]. The application of fungicides is the conventional method of managing PM in most cucumber production areas[3]. In response to growing consumer concerns for pesticide residues, alternative/additional strategies for disease control are required[4].
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