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Abstract
BackgroundEnormous work has shown that polyamines are involved in a variety of physiological processes, but information is scarce on the potential of modifying disease response through genetic transformation of a polyamine biosynthetic gene.ResultsIn the present work, an apple spermidine synthase gene (MdSPDS1) was introduced into sweet orange (Citrus sinensis Osbeck 'Anliucheng') via Agrobacterium-mediated transformation of embryogenic calluses. Two transgenic lines (TG4 and TG9) varied in the transgene expression and cellular endogenous polyamine contents. Pinprick inoculation demonstrated that the transgenic lines were less susceptible to Xanthomonas axonopodis pv. citri (Xac), the causal agent of citrus canker, than the wild type plants (WT). In addition, our data showed that upon Xac attack TG9 had significantly higher free spermine (Spm) and polyamine oxidase (PAO) activity when compared with the WT, concurrent with an apparent hypersensitive response and the accumulation of more H2O2. Pretreatment of TG9 leaves with guazatine acetate, an inhibitor of PAO, repressed PAO activity and reduced H2O2 accumulation, leading to more conspicuous disease symptoms than the controls when both were challenged with Xac. Moreover, mRNA levels of most of the defense-related genes involved in synthesis of pathogenesis-related protein and jasmonic acid were upregulated in TG9 than in the WT regardless of Xac infection.ConclusionOur results demonstrated that overexpression of the MdSPDS1 gene prominently lowered the sensitivity of the transgenic plants to canker. This may be, at least partially, correlated with the generation of more H2O2 due to increased production of polyamines and enhanced PAO-mediated catabolism, triggering hypersensitive response or activation of defense-related genes.
Highlights
Enormous work has shown that polyamines are involved in a variety of physiological processes, but information is scarce on the potential of modifying disease response through genetic transformation of a polyamine biosynthetic gene
We showed that two transgenic lines (TG) with varying mRNA levels of the transgene were less susceptible to Xanthomonas axonopodis pv. citri (Xac) than the wild type plants (WT), which might be correlated with production of H2O2 and/or up-regulation of transcription levels of defense-related genes
Antioxidant enzymes have been shown to be important for homeostasis of reactive oxygen species (ROS), so we examined activities of two enzymes involved in H2O2 production and scavenging, superoxide dismutase (SOD) and catalase (CAT), in the WT and TG9 at 1, 2 and 3 days post inoculation (DPI)
Summary
Enormous work has shown that polyamines are involved in a variety of physiological processes, but information is scarce on the potential of modifying disease response through genetic transformation of a polyamine biosynthetic gene. World citrus industry is frequently confronted with risk of devastation by a variety of biotic or abiotic stresses. Citri (Xac), is one of the most destructive biotic stresses threatening the citrus production globally [1,2]. The typical symptoms of canker caused by Xac the primary strategies for controlling canker disease depend upon an integrated approach including eradication program and use of antibiotics or bactericides [6]. Breeding a cultivar resistant to Xac provides the most effective and economical way to control this disease. Genetic engineering paves the way for creating novel germplasms that are otherwise impossible via classic breeding strategy, and has been widely employed to produce diseaseresistant materials without greatly altering existing genetic background [7]
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