Abstract
Harpin proteins as elicitor derived from plant gram negative bacteria such as Xanthomonas oryzae pv. oryzae (Xoo), Erwinia amylovora induce disease resistance in plants by activating multiple defense responses. However, it is unclear whether phytoalexin production and ROS burst are involved in the disease resistance conferred by the expression of the harpinXoo protein in rice. In this article, ectopic expression of hrf1 in rice enhanced resistance to bacterial blight. Accompanying with the activation of genes related to the phytoalexin biosynthesis pathway in hrf1-transformed rice, phytoalexins quickly and consistently accumulated concurrent with the limitation of bacterial growth rate. Moreover, the hrf1-transformed rice showed an increased ability for ROS scavenging and decreased hydrogen peroxide (H2O2) concentration. Furthermore, the localization and relative quantification of silicon deposition in rice leaves was detected by scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometer (EDS). Finally, the transcript levels of defense response genes increased in transformed rice. These results show a correlation between Xoo resistance and phytoalexin production, H2O2, silicon deposition and defense gene expression in hrf1-transformed rice. These data are significant because they provide evidence for a better understanding the role of defense responses in the incompatible interaction between bacterial disease and hrf1-transformed plants. These data also supply an opportunity for generating nonspecific resistance to pathogens.
Highlights
Bacterial blight is one of the most destructive rice diseases
We previously reported that the harpinXoo-encoding gene hrf1, derived from Xanthomonas oryzae pv. oryzae (Xoo) and driven by the constitutive 35S promoter, was transferred into the japonica rice cultivar R109 by Agrobacteriummediated transformation
We showed that ectopic expression of hrf1 in rice significantly enhanced resistance to Xoo strains, accompanied by high and rapid induction of phytoalexins production and changed the distribution of silicified dumbbell-shaped cells and papillae
Summary
Bacterial blight is one of the most destructive rice diseases. It is caused by Xoo, and results in 10% to 80% yield losses, endangering worldwide food security [1]. An economically effective and environmentally sound approach to control disease is the utilization of cultivars that possessed durable, nonspecific, broadspectrum resistance by incorporating an elicitor protein harpinencoding gene into susceptible rice with good agronomic traits [2]. We still know little about the signal transduction network of disease resistance induced by harpin proteins in plants. As one kind of special compound, harpin protein elicitors provide a potential opportunity for the generation of durable broad-spectrum disease resistance in plants. Protein elicitors induce a hypersensitive response and multiple defense responses in non-hosts and determine pathogenicity in host plants [3,4]. HarpinEa, purified from the gram-negative plant pathogenic bacteria Erwinia amylovora, activates ROS burst, salicylic acid (SA)
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