Abstract
BackgroundApple canker is a devastating branch disease caused by Valsa mali (Vm). The endophytic actinomycete Saccharothrix yanglingensis Hhs.015 (Sy Hhs.015) can effectively inhibit the growth of Vm. To reveal the mechanism, by which Vm respond to Sy Hhs.015, the transcriptome of Vm was analyzed using RNA-seq technology.ResultsCompared with normal growing Vm in the control group, 1476 genes were significantly differentially expressed in the Sy Hhs.015’s treatment group, of which 851 genes were up-regulated and 625 genes were down-regulated. Combined gene function and pathway analysis of differentially expressed genes (DEGs) revealed that Sy Hhs.015 affected the carbohydrate metabolic pathway, which is utilized by Vm for energy production. Approximately 82% of the glycoside hydrolase genes were down-regulated, including three pectinase genes (PGs), which are key pathogenic factors. The cell wall structure of Vm was disrupted by Sy Hhs.015 and cell wall-related genes were found to be down-regulated. Of the peroxisome associated genes, those encoding catalase (CAT) and superoxide dismutase (SOD) which scavenge reactive oxygen species (ROS), as well as those encoding AMACR and ACAA1 which are related to the β-oxidation of fatty acids, were down-regulated. MS and ICL, key genes in glyoxylate cycle, were also down-regulated. In response to the stress of Sy Hhs.015 exposure, Vm increased amino acid metabolism to synthesize the required nitrogenous compounds, while alpha-keto acids, which involved in the TCA cycle, could be used to produce energy by deamination or transamination. Retinol dehydrogenase, associated with cell wall dextran synthesis, and sterol 24-C-methyltransferase, related to cell membrane ergosterol synthesis, were up-regulated. The genes encoding glutathione S-transferase, (GST), which has antioxidant activity and ABC transporters which have an efflux function, were also up-regulated.ConclusionThese results show that the response of Vm to Sy Hhs.015 exposure is a complicated and highly regulated process, and provide a theoretical basis for both clarifying the biocontrol mechanism of Sy Hhs.015 and the response of Vm to stress.
Highlights
Apple canker is a devastating branch disease caused by Valsa mali (Vm)
The nucleus had fully separated from the cytoplasm, while several cells had even completely degraded in the nucleus (Fig. 1e and f )
Sequencing quality control, quantification of gene expression levels, and annotation of gene function The quality of extracted RNA reaches the standard of sequencing, and the mass concentration of each sample is higher than 36 ng/μL (Additional file 1: Table S1)
Summary
Apple canker is a devastating branch disease caused by Valsa mali (Vm). Apple canker is a serious and potential devastating branch disease caused by the ascomycetous fungus, Valsa mali (Vm), which occurs in the main apple producing areas of China [1], and causes serious economic losses. Vm has latent infection characteristics, as observed from the fact that decomposition of apple branches that look apparently free from disease can occur after specific treatments [4]. The process of Vm infecting apple trees is complicated, and cell wall- degrading enzymes, secondary metabolites, and effector proteins might play important roles in their pathogenic mechanism [5]. During the process of infecting apple bark, the expression of genes related to catabolism, hydrolase activity and secondary metabolite biosynthesis are up-regulated [6]. Some genes related to toxin synthesis have been identified in the genome of Vm, and genes related to secondary metabolism such as cytochrome P450, non-ribosomal polypeptide synthetase and monooxygenase, have been shown to be up-regulated during infection [5]
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