Molecular Plant Advance Access published online on May 8, 2008
Molecular Plant, doi:10.1093/mp/ssn020
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© The Author 2008. Published by Oxford University Press on behalf of CSPP and IPPE, SIBS, CAS.
Stress- and Pathogen-Induced Arabidopsis WRKY48 is a Transcriptional Activator that Represses Plant Basal Defense
a Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907–2054, USA
b Present address: Department of Botany, Miami University, Oxford, Ohio 45056, USA
1 To whom correspondence should be addressed. E-mail zhixiang{at}purdue.edu, fax 765-494-5896.
Plant WRKY transcription factors can function as either positive or negative regulators of plant basal disease resistance. Arabidopsis WRKY48 is induced by mechanical and/or osmotic stress due to infiltration and pathogen infection and, therefore, may play a role in plant defense responses. WRKY48 is localized to the nucleus, recognizes the TTGACC W-box sequence with a high affinity in vitro and functions in plant cells as a strong transcriptional activator. To determine the biological functions directly, we have isolated loss-of-function T-DNA insertion mutants and generated gain-of-function transgenic overexpression plants for WRKY48 in Arabidopsis. Growth of a virulent strain of the bacterial pathogen Pseudomonas syringae was decreased in the wrky48 T-DNA insertion mutants. The enhanced resistance of the loss-of-function mutants was associated with increased induction of salicylic acid-regulated PR1 by the bacterial pathogen. By contrast, transgenic WRKY48-overexpressing plants support enhanced growth of P. syringae and the enhanced susceptibility was associated with reduced expression of defense-related PR genes. These results suggest that WRKY48 is a negative regulator of PR gene expression and basal resistance to the bacterial pathogen P. syringae.