Abstract
Citrus canker disease caused by Xanthomonas citri subsp. citri (Xcc) is one of the most devastating diseases affecting the citrus industry worldwide. In our previous study, the canker-resistant transgenic sweet orange (Citrus sinensis Osbeck) plants were produced via constitutively overexpressing a spermidine synthase. To unravel the molecular mechanisms underlying Xcc resistance of the transgenic plants, in the present study global transcriptional profiling was compared between untransformed line (WT) and the transgenic line (TG9) by hybridizing with Affymetrix Citrus GeneChip. In total, 666 differentially expressed genes (DEGs) were identified, 448 upregulated, and 218 downregulated. The DEGs were classified into 33 categories after Gene ontology (GO) annotation, in which 68 genes are in response to stimulus and involved in immune system process, 12 genes are related to cell wall, and 13 genes belong to transcription factors. These genes and those related to starch and sucrose metabolism, glutathione metabolism, biosynthesis of phenylpropanoids, and plant hormones were hypothesized to play major roles in the canker resistance of TG9. Semiquantitative RT-PCR analysis showed that the transcript levels of several candidate genes in TG9 were significantly higher than in WT both before and after Xcc inoculation, indicating their potential association with canker disease.
Highlights
Citrus canker disease caused by a biotrophic bacterium Xanthomonas citri subsp. citri (Xcc) is one of the most devastating diseases in many citrus-producing regions. is disease results in defoliation, dieback, and premature fruit drop, leading to enormous loss of yield and fruit quality [1, 2]
To reveal the molecular mechanisms underlying canker resistance in TG9, the global transcriptional pro ling of TG9 and WT were compared by citrus genome Genechip analysis
Ectopic expression of a polyamine biosynthetic gene (MdSPDS1) in sweet orange confers citrus canker resistance, and transcript levels of several defenserelated genes were induced in the transgenic line [6]. erefore, we speculate that global transcriptional levels of transgenic plants are regulated due to the overexpression of MdSPDS1, which may explain at the transcriptional level the enhanced resistance in the transgenic plants
Summary
Citrus canker disease caused by a biotrophic bacterium Xanthomonas citri subsp. citri (Xcc) is one of the most devastating diseases in many citrus-producing regions. is disease results in defoliation, dieback, and premature fruit drop, leading to enormous loss of yield and fruit quality [1, 2]. Citri (Xcc) is one of the most devastating diseases in many citrus-producing regions. Current strategies for counteracting with canker disease are primarily directed to integrated approaches such as eradication programme and use of antibiotics or bactericides [2]. Due to the disadvantages in labor investment, safety, consistency, and stabilization these strategies are not the ultimate solutions. Their applications are o en compromised by inducing adverse environmental in uence and change of pathogen strains. Genetic manipulation via transforming stress-related genes is a widely employed way to create disease-resistant germplasms that are otherwise impossible for classic breeding programme, especially in citrus. Antibacterial peptides, R-genes, pathogenic factors, and defense-related genes have
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