Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 112, Issue 30, Pages 9166-9173Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1511182112
Keywords
plant immunity; transcription regulation; circadian clock; systemic acquired resistance; stomatal immunity
Categories
Funding
- National Science Foundation [IOS 0929226]
- NIH [1R01-GM099839-01]
- Howard Hughes Medical Institute-Gordon and Betty Moore Foundation [GBMF3032]
- NIH-National Institute of General Medical Sciences [R01GM056006, R01GM067837, RC2GM092412]
- Hargitt Fellowship
- Direct For Biological Sciences
- Division Of Integrative Organismal Systems [0929226] Funding Source: National Science Foundation
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The plant hormone salicylic acid (SA) is essential for local defense and systemic acquired resistance (SAR). When plants, such as Arabidopsis, are challenged by different pathogens, an increase in SA biosynthesis generally occurs through transcriptional induction of the key synthetic enzyme isochorismate synthase 1 (ICS1). However, the regulatory mechanism for this induction is poorly understood. Using a yeast one-hybrid screen, we identified two transcription factors (TFs), NTM1-LIKE 9 (NTL9) and CCA1 HIKING EXPEDITION (CHE), as activators of ICS1 during specific immune responses. NTL9 is essential for inducing ICS1 and two other SA synthesis-related genes, PHYTOALEXIN-DEFICIENT 4 (PAD4) and ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1), in guard cells that form stomata. Stomata can quickly close upon challenge to block pathogen entry. This stomatal immunity requires ICS1 and the SA signaling pathway. In the ntl9 mutant, this response is defective and can be rescued by exogenous application of SA, indicating that NTL9-mediated SA synthesis is essential for stomatal immunity. CHE, the second identified TF, is a central circadian clock oscillator and is required not only for the daily oscillation in SA levels but also for the pathogen-induced SA synthesis in systemic tissues during SAR. CHE may also regulate ICS1 through the known transcription activators CALMODULIN BINDING PROTEIN 60g (CBP60g) and SYSTEMIC ACQUIRED RESISTANCE DEFICIENT 1 (SARD1) because induction of these TF genes is compromised in the che-2 mutant. Our study shows that SA biosynthesis is regulated by multiple TFs in a spatial and temporal manner and therefore fills a gap in the signal transduction pathway between pathogen recognition and SA production.
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