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Ascorbic Acid Deficiency in Arabidopsis Induces Constitutive Priming That is Dependent on Hydrogen Peroxide, Salicylic Acid, and the NPR1 Gene

March 2010 , Volume 23 , Number  3
Pages  340 - 351

Madhumati Mukherjee,1 Katherine E. Larrimore,1 Naushin J. Ahmed,1 Tyler S. Bedick,1 Nadia T. Barghouthi,1 M. Brian Traw,2 and Carina Barth1

1Department of Biology, West Virginia University, 53 Campus Drive, Morgantown 26506, U.S.A.; 2Department of Biological Sciences, University of Pittsburgh, 4249 Fifth Avenue, Pittsburgh, PA 15260, U.S.A.

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Accepted 20 October 2009.

The ascorbic acid (AA)-deficient Arabidopsis thaliana vtc1-1 mutant exhibits increased resistance to the virulent bacterial pathogen Pseudomonas syringae. This response correlates with heightened levels of salicylic acid (SA), which induces antimicrobial pathogenesis-related (PR) proteins. To determine if SA-mediated, enhanced disease resistance is a general phenomenon of AA deficiency, to elucidate the signal that stimulates SA synthesis, and to identify the biosynthetic pathway through which SA accumulates, we studied the four AA-deficient vtc1-1, vtc2-1, vtc3-1, and vtc4-1 mutants. We also studied double mutants defective in the AA-biosynthetic gene VTC1 and the SA signaling pathway genes PAD4, EDS5, and NPR1, respectively. All vtc mutants were more resistant to P. syringae than the wild type. With the exception of vtc4-1, this correlated with constitutively upregulated H2O2, SA, and messenger RNA levels of PR genes. Double mutants exhibited decreased SA levels and enhanced susceptibility to P. syringae compared with the wild type, suggesting that vtc1-1 requires functional PAD4, EDS5, and NPR1 for SA biosynthesis and pathogen resistance. We suggest that AA deficiency causes constitutive priming through a buildup of H2O2 that stimulates SA accumulation, conferring enhanced disease resistance in vtc1-1, vtc2-1, and vtc3-1, whereas vtc4-1 might be sensitized to H2O2 and SA production after infection.

© 2010 The American Phytopathological Society