European Journal of Plant Pathology

, Volume 128, Issue 1, pp 91–100 | Cite as

Over-expression of the Arabidopsis NPR1 gene in citrus increases resistance to citrus canker

  • Xudong Zhang
  • Marta I. Francis
  • William O. Dawson
  • James H. Graham
  • Vladimir Orbović
  • Eric W. Triplett
  • Zhonglin Mou


Citrus canker, caused by the bacterial pathogen Xanthomonas citri subsp. citri (Xcc), is a serious leaf and fruit spotting disease affecting many important citrus cultivars including grapefruit and certain sweet oranges. Currently, efficacious and economical disease control measures for highly susceptible citrus cultivars are lacking. Development of commercial cultivars with greater field resistance to citrus canker is the optimum strategy for effective disease management. In this study, we generated transgenic ‘Duncan’ grapefruit (DG) and ‘Hamlin’ sweet orange (Ham) expressing the Arabidopsis NPR1 gene (AtNPR1), which is a key positive regulator of the long-lasting broad-spectrum resistance known as systemic acquired resistance (SAR). Our results indicate that over-expression of AtNPR1 in citrus increases resistance to citrus canker and that the resistance is related with the expression levels of AtNPR1 in the transgenic plants. The line (DG 42-2) with the highest expression level of AtNPR1 was also the most resistant, which developed significant fewer lesions accompanied by a ten-fold reduction in Xcc population. The lesions developed on DG 42-2 were smaller and darker than those on the control and lacked callus formation. These lesion phenotypes resemble those on canker resistant kumquats and canker susceptible citrus trees treated with SAR-inducing compounds. Therefore, over-expression of AtNPR1 in citrus is a promising approach for development of more resistant cultivars to citrus canker.


Citrus canker Systemic acquired resistance Pathogenesis-related protein Xanthomonas citri 



salicylic acid


Arabidopsis nonexpressor of pathogenesis-related genes 1


systemic acquired resistance


pathogenesis-related protein 2


2,6-dichloroisonicotinic acid


benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester






Xanthomonas citri ssp. citri


Pseudomonas syringae pv. maculicola


hypersensitive response



This work was supported by grants from Florida Citrus Production Research Advisory Council (FCPRAC) awarded to Z.M., W.D., and J.H.G. and a grant from the National Science Foundation (IOS-0842716) awarded to Z.M.. The authors are grateful to Dr. Xinnian Dong (Duke University) for the pKEx4tr-AtNPR1 cDNA plasmid and Dr. Sixue Chen (University of Florida) for access to the HPLC equipment. The authors thank Cecile Robertson and Alma Peña for technical assistance.


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Copyright information

© KNPV 2010

Authors and Affiliations

  • Xudong Zhang
    • 1
  • Marta I. Francis
    • 2
  • William O. Dawson
    • 2
  • James H. Graham
    • 2
  • Vladimir Orbović
    • 2
  • Eric W. Triplett
    • 1
  • Zhonglin Mou
    • 1
  1. 1.Department of Microbiology and Cell ScienceUniversity of FloridaGainesvilleUSA
  2. 2.Citrus Research and Education CenterUniversity of FloridaLake AlfredUSA

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