Abstract
Plant defense responses are tightly controlled by many positive and negative regulators to cope with attacks from various pathogens. Arabidopsis (Arabidopsis thaliana) ENHANCED DISEASE RESISTANCE2 (EDR2) is a negative regulator of powdery mildew resistance, and edr2 mutants display enhanced resistance to powdery mildew (Golovinomyces cichoracearum). To identify components acting in the EDR2 pathway, we screened for edr2 suppressors and identified a gain-of-function mutation in SIGNAL RESPONSIVE1 (SR1), which encodes a calmodulin-binding transcription activator. The sr1-4D gain-of-function mutation suppresses all edr2-associated phenotypes, including powdery mildew resistance, mildew-induced cell death, and ethylene-induced senescence. The sr1-4D single mutant is more susceptible to a Pseudomonas syringae pv tomato DC3000 virulent strain and to avirulent strains carrying avrRpt2 or avrRPS4 than the wild type. We show that SR1 directly binds to the promoter region of NON-RACE-SPECIFIC DISEASE RESISTANCE1 (NDR1), a key component in RESISTANCE TO PSEUDOMONAS SYRINGAE2-mediated plant immunity. Also, the ndr1 mutation suppresses the sr1-1 null allele, which shows enhanced resistance to both P. syringae pv tomato DC3000 avrRpt2 and G. cichoracearum. In addition, we show that SR1 regulates ethylene-induced senescence by directly binding to the ETHYLENE INSENSITIVE3 (EIN3) promoter region in vivo. Enhanced ethylene-induced senescence in sr1-1 is suppressed by ein3. Our data indicate that SR1 plays an important role in plant immunity and ethylene signaling by directly regulating NDR1 and EIN3.
Highlights
Plant defense responses are tightly controlled by many positive and negative regulators to cope with attacks from various pathogens
To identify components that are involved in ENHANCED DISEASE RESISTANCE2 (EDR2) signaling, we screened for mutants that suppressed the edr2 enhanced resistance phenotype
We identified a number of suppressors, including mutations in PHYTOALEXIN DEFICIENT4 (PAD4), SALICYLIC ACID INDUCTION-DEFICIENT2 (SID2), NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1 (NPR1), and AGD2-LIKE DEFENSE RESPONSE PROTEIN1 (ALD1), indicating that the screen was highly efficient (Nie et al, 2011)
Summary
Plant defense responses are tightly controlled by many positive and negative regulators to cope with attacks from various pathogens. To identify components acting in the EDR2 pathway, we screened for edr suppressors and identified a gain-of-function mutation in SIGNAL RESPONSIVE1 (SR1), which encodes a calmodulin-binding transcription activator. Our data indicate that SR1 plays an important role in plant immunity and ethylene signaling by directly regulating NDR1 and EIN3. CAM-BINDING PROTEIN 60G (CBP60g), a member of the Arabidopsis CBP60 gene family, regulates microbeassociated molecular pattern signaling and SA accumulation through calcium-dependent calmodulin binding (Wang et al, 2009). We show that a gain-of-function mutation in the calmodulinbinding motif of SR1 suppressed edr2-mediated resistance to powdery mildew and enhanced ET-induced senescence in edr. We show that SR1 regulates plant defense responses and senescence by directly binding to the promoter regions of NDR1 and ETHYLENE INSENSITIVE3 (EIN3)
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