jasmonic-acid and Pseudomonas-Infections

Topics: Brassica napus; Cells, Cultured; Cyclopentanes; Ethylenes; Gene Expression Profiling; Immunity, Innate; Opportunistic Infections; Organ Specificity; Oxylipins; Plant Growth Regulators; Plant Immunity; Pseudomonas aeruginosa; Pseudomonas Infections; Salicylic Acid; Signal Transduction; Up-Regulation

To efficiently counteract pathogens, plants rely on a complex set of immune responses that are tightly regulated to allow the timely activation, appropriate duration and adequate amplitude of defense programs. The coordination of the plant immune response is known to require the activity of the ubiquitin/proteasome system, which controls the stability of proteins in eukaryotes. Here, we demonstrate that the N-end rule pathway, a subset of the ubiquitin/proteasome system, regulates the defense against a wide range of bacterial and fungal pathogens in the model plant Arabidopsis thaliana. We show that this pathway positively regulates the biosynthesis of plant-defense metabolites such as glucosinolates, as well as the biosynthesis and response to the phytohormone jasmonic acid, which plays a key role in plant immunity. Our results also suggest that the arginylation branch of the N-end rule pathway regulates the timing and amplitude of the defense program against the model pathogen Pseudomonas syringae AvrRpm1.

Topics: Arabidopsis; Arabidopsis Proteins; Cyclopentanes; Gene Expression Regulation, Plant; Glucosinolates; Oxylipins; Plant Diseases; Plant Growth Regulators; Plant Immunity; Proteasome Endopeptidase Complex; Pseudomonas Infections; Pseudomonas syringae; Ubiquitin

Coronatine is an important virulence factor produced by several pathovars of the bacterial pathogen Pseudomonas syringae. The structure of coronatine is similar to that of a class of plant hormones called jasmonates (JAs). An important step in JA signaling is the SCF(COI1) E3 ubiquitin ligase-dependent degradation of JAZ repressor proteins. We have recently shown that jasmonoyl isoleucine (JA-Ile) promotes physical interaction between Arabidopsis JAZ1 and COI1 (the F-box component of SCF(COI1)) proteins, and that the JA-Ile-dependent COI1-JAZ1 interaction could be reconstituted in yeast cells (i.e. in the absence of other plant proteins). Here we show that coronatine, but not its two biosynthetic precursors, also promotes interaction between Arabidopsis COI1 and multiple JAZ proteins. The C-terminal Jas motif, but not the N-terminal (NT) domain or central ZIM domain of JAZ proteins, is critical for JA-Ile/coronatine-dependent interaction with COI1. Two positively charged amino acid residues in the Jas domain were identified as essential for coronatine-dependent COI1-JAZ interactions. Mutations of these two residues did not affect the ability of JAZ1 and JAZ9 to interact with the transcription factor AtMYC2. Importantly, transgenic Arabidopsis plants expressing JAZ1 carrying these two mutations exhibited JA-insensitive phenotypes, including male sterility and enhanced resistance to P. syringae infection. These results not only suggest that coronatine and JA-Ile target the physical interaction between COI1 and the Jas domain of JAZ repressors, but also illustrate the critical role of positively charged amino acids in the Jas domain in mediating the JA-Ile/coronatine-dependent JAZ interaction with COI1.

Topics: Amino Acid Motifs; Amino Acids; Arabidopsis; Arabidopsis Proteins; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Cyclopentanes; DNA, Complementary; F-Box Proteins; Genes, Plant; Indenes; Isoleucine; Mutagenesis, Site-Directed; Mutation; Nuclear Proteins; Oxylipins; Phenotype; Plant Diseases; Plant Growth Regulators; Plants, Genetically Modified; Protein Interaction Domains and Motifs; Pseudomonas Infections; Pseudomonas syringae; Repressor Proteins; Saccharomyces cerevisiae; Two-Hybrid System Techniques

Transposon inactivation of Arabidopsis MAP kinase 4 produced the mpk4 mutant exhibiting constitutive systemic acquired resistance (SAR) including elevated salicylic acid (SA) levels, increased resistance to virulent pathogens, and constitutive pathogenesis-related gene expression shown by Northern and microarray hybridizations. MPK4 kinase activity is required to repress SAR, as an inactive MPK4 form failed to complement mpk4. Analysis of mpk4 expressing the SA hydroxylase NahG and of mpk4/npr1 double mutants indicated that SAR expression in mpk4 is dependent upon elevated SA levels but is independent of NPR1. PDF1.2 and THI2.1 gene induction by jasmonate was blocked in mpk4 expressing NahG, suggesting that MPK4 is required for jasmonic acid-responsive gene expression.

Topics: Alleles; Arabidopsis; Arabidopsis Proteins; Blotting, Northern; Cold Temperature; Cyclopentanes; Desiccation; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; Hot Temperature; Immunity, Innate; Mutation; Oxylipins; Plant Diseases; Plant Growth Regulators; Plant Proteins; Protein Tyrosine Phosphatases; Pseudomonas; Pseudomonas Infections; RNA, Messenger; Salts; Transcriptional Activation