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Ca2+/calmodulin regulates salicylic-acid-mediated plant immunity

Abstract

Intracellular calcium transients during plant–pathogen interactions are necessary early events leading to local and systemic acquired resistance1. Salicylic acid, a critical messenger, is also required for both of these responses2,3, but whether and how salicylic acid level is regulated by Ca2+ signalling during plant–pathogen interaction is unclear. Here we report a mechanism connecting Ca2+ signal to salicylic-acid-mediated immune response through calmodulin, AtSR1 (also known as CAMTA3), a Ca2+/calmodulin-binding transcription factor, and EDS1, an established regulator of salicylic acid level. Constitutive disease resistance and elevated levels of salicylic acid in loss-of-function alleles of Arabidopsis AtSR1 suggest that AtSR1 is a negative regulator of plant immunity. This was confirmed by epistasis analysis with mutants of compromised salicylic acid accumulation and disease resistance. We show that AtSR1 interacts with the promoter of EDS1 and represses its expression. Furthermore, Ca2+/calmodulin-binding to AtSR1 is required for suppression of plant defence, indicating a direct role for Ca2+/calmodulin in regulating the function of AtSR1. These results reveal a previously unknown regulatory mechanism linking Ca2+ signalling to salicylic acid level.

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Figure 1: The Atsr1-1 mutant shows sensitized defence responses.
Figure 2: The pleiotropic phenotype of Atsr1-1 is dependent on salicylic acid.
Figure 3: AtSR1 is involved in transcriptional regulation of EDS1.
Figure 4: Repression of immune response by AtSR1 is regulated by Ca 2+ /CaM.

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Acknowledgements

Constructs and transgenic lines produced in this research are available on request. This research was supported by United States Department of Agriculture grants 2002-00741, 2005-01107 and 2008-01034, National Science Foundation grants MCB-0424898, MCB-0424895, DBI 0743097 and IOS-0642146, Colorado Sate University Academic Enrichment Program grant 180470, Office of Naval Research N0014-08-1-0470 and the Washington State University Agricultural Research Center. We also thank I. Day for her comments on the manuscript and A. Mochel for her help in preparing the manuscript.

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Correspondence to B. W. Poovaiah.

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Du, L., Ali, G., Simons, K. et al. Ca2+/calmodulin regulates salicylic-acid-mediated plant immunity. Nature 457, 1154–1158 (2009). https://doi.org/10.1038/nature07612

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