Brassinosteroids are known to protect plants against various abiotic and biotic stresses, however, very limited information is available about the role of progesterone. Therefore the effects of Pseudomonas syringae pv. syringae (P.s.) wild type strain 61, its hrcC mutant, and the saprophytic P. fluorescens (P.f.) strain 55 were investigated in wild type Arabidopsis thaliana cv. Columbia and its rbohF knock-out mutant, with and without progesterone pre-treatment. The reactions of wild type and rbohF mutant Arabidopsis to bacterial inoculations were similar, although 2 h after injection of P.s. a larger increase of electrolyte leakage was measured in wild type than in rbohF knockout mutant leaves. The hrcC mutant caused weak necrotic symptoms and increased leakage in both types of Arabidopsis, although to a much lesser extent than P.s. The P.f. did not induce any visible symptom, but slightly increased the electrolyte leakage in both types of Arabidopsis. Inoculation by all Pseudomonas bacteria led to significant alterations in photosystem 2 efficiency as compared to control plants. Pre-treatment of leaves with progesterone diminished the necrotic symptoms, the electrolyte leakage and improve the efficiency of photosystem 2 caused by Pseudomonas bacteria.

Brassinosteroids are known to protect plants against various abiotic and biotic stresses, however, very limited information is available about the role of progesterone. Therefore the effects of Pseudomonas syringae pv. syringae (P.s.) wild type strain 61, its hrcC mutant, and the saprophytic P. fluorescens (P.f.) strain 55 were investigated in wild type Arabidopsis thaliana cv. Columbia and its rbohF knock-out mutant, with and without progesterone pre-treatment. The reactions of wild type and rbohF mutant Arabidopsis to bacterial inoculations were similar, although 2 h after injection of P.s. a larger increase of electrolyte leakage was measured in wild type than in rbohF knockout mutant leaves. The hrcC mutant caused weak necrotic symptoms and increased leakage in both types of Arabidopsis, although to a much lesser extent than P.s. The P.f. did not induce any visible symptom, but slightly increased the electrolyte leakage in both types of Arabidopsis. Inoculation by all Pseudomonas bacteria led to significant alterations in photosystem 2 efficiency as compared to control plants. Pre-treatment of leaves with progesterone diminished the necrotic symptoms, the electrolyte leakage and improve the efficiency of photosystem 2 caused by Pseudomonas bacteria.

The Arabidopsis thaliana (L.) Heynh. atExt1 extensin gene is expressed in a cell and tissue-specific manner, in response to developmental cues, and is inducible by a wide range of biotic and abiotic stresses. Over-expression of this gene has been shown to alter stem morphology and to limit the invasiveness of virulent bacterial pathogens, indicating that this cell wall protein gene plays an important role in plant development and defense. A detailed sequence analysis of 3.2 kb of the atExt1 gene promoter region has identified a large number of putative 5'cis-acting elements. Based on the location of clusters of putative promoter control elements, seven atExt1 5' promoter truncations were constructed, fused upstream of the β-glucuronidase (GUS) reporter gene, and transformed into A. thaliana. Transgenic plants carrying the various promoter constructs were challenged by wounding and pathogen attack and analysed for GUS expression - this analysis revealed a complex pattern of regulation, involving positive and negative control regions. Northern analysis using wounded tissues from transgenic Arabidopsis plants carrying the 3.2 kb-promoter::GUS construct confirmed the transcriptional activation of the transgene.

The Arabidopsis thaliana (L.) Heynh. atExt1 extensin gene is expressed in a cell and tissue-specific manner, in response to developmental cues, and is inducible by a wide range of biotic and abiotic stresses. Over-expression of this gene has been shown to alter stem morphology and to limit the invasiveness of virulent bacterial pathogens, indicating that this cell wall protein gene plays an important role in plant development and defense. A detailed sequence analysis of 3.2 kb of the atExt1 gene promoter region has identified a large number of putative 5′cis-acting elements. Based on the location of clusters of putative promoter control elements, seven atExt1 5′ promoter truncations were constructed, fused upstream of the β-glucuronidase (GUS) reporter gene, and transformed into A. thaliana. Transgenic plants carrying the various promoter constructs were challenged by wounding and pathogen attack and analysed for GUS expression - this analysis revealed a complex pattern of regulation, involving positive and negative control regions. Northern analysis using wounded tissues from transgenic Arabidopsis plants carrying the 3.2 kb-promoter::GUS construct confirmed the transcriptional activation of the transgene.

The Arabidopsis thaliana atExt1 extensin gene is expressed in a cell and tissue-specific manner, in response to developmental cues, and is inducible by a wide range of biotic and abiotic stresses. Over-expression of this gene has been shown to alter stem morphology and to limit the invasiveness of virulent bacterial pathogens, indicating that this cell wall protein gene plays an important role in plant development and defense. A detailed sequence analysis of 3.2 kb of the atExt1 gene promoter region has identified a large number of putative 5 cis-acting elements. Based on the location of clusters of putative promoter control elements, seven atExt1 5 promoter truncations were constructed, fused upstream of the beta-glucuronidase (GUS) reporter gene, and transformed into A. thaliana. Transgenic plants carrying the various promoter constructs were challenged by wounding and pathogen attack and analysed for GUS expression - this analysis revealed a complex pattern of regulation, involving positive and negative control regions. Northern analysis using wounded tissues from transgenic Arabidopsis plants carrying the 3.2 kb-promoter:GUS construct confirmed the transcriptional activation of the transgene.

Recent reports have revealed new guard cell signaling elements that function in stomatal defense in Arabidopsis thaliana (Arabidopsis). We discuss here the role of oxylipins, salicylic acid (SA), and abscisic acid (ABA) in stomatal immunity in response to the bacterial pathogen Pseudomonas syringae.

International audience | Recent reports have revealed new guard cell signaling elements that function in stomatal defense in <em>Arabidopsis thaliana</em> (<em>Arabidopsis</em>). We discuss here the role of oxylipins, salicylic acid (SA), and abscisic acid (ABA) in stomatal immunity in response to the bacterial pathogen <em>Pseudomonas syringae</em>.