The Arabidopsis hrl1 mutation reveals novel overlapping roles for salicylic acid, jasmonic acid and ethylene signalling in cell death and defence against pathogens

• Published in: The Plant journal : for cell and molecular biology 2002-05, Vol.30 (4), p.467-480
• Main Authors: Devadas, Sendil K., Enyedi, Alexander, Raina, Ramesh
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Apoptosis - drug effects; Apoptosis - physiology; Arabidopsis; Arabidopsis - drug effects; Arabidopsis - genetics; Arabidopsis - microbiology; Arabidopsis Proteins; Bacteria - growth & development; Biological and medical sciences; cell death; Cyclopentanes - metabolism; Cyclopentanes - pharmacology; Defensins; Ethylenes - metabolism; Ethylenes - pharmacology; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant - drug effects; Genetics and breeding of economic plants; Glucans - metabolism; hrl1; Hydrogen Peroxide - metabolism; Immunity, Innate - genetics; Mixed Function Oxygenases - genetics; Mutation; Oomycetes - growth & development; Oxygen - metabolism; Oxylipins; pathogen resistance; PDF1.2; Pest resistance; Phenotype; Plant Diseases - genetics; Plant Diseases - microbiology; Plant Growth Regulators - metabolism; Plant Growth Regulators - pharmacology; Plant pathogens; Plant Proteins - genetics; Reactive Oxygen Species - metabolism; Salicylic Acid - metabolism; Salicylic Acid - pharmacology; Signal Transduction - drug effects; Varietal selection. Specialized plant breeding, plant breeding aims
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1046/j.1365-313X.2002.01300.x

Summary Defence against pathogens in Arabidopsis is orchestrated by at least three signalling molecules: salicylic acid (SA), jasmonic acid (JA) and ethylene (ET). The hrl1 (hypersensitive response‐like lesions 1) mutant of Arabidopsis is characterized by spontaneous necrotic lesions, accumulation of reactive oxygen species, constitutive expression of SA‐ and ET/JA‐responsive defence genes, and enhanced resistance to virulent bacterial and oomycete pathogens. Epistasis analyses of hrl1 with npr1, etr1, coi1 and SA‐depleted nahG plants revealed novel interactions between SA and ET/JA signalling pathways in regulating defence gene expression and cell death. RNA gel‐blot analysis of RNA isolated separately from the lesion+ and the lesion– leaves of double mutants of hrl1 revealed different signalling requirements for the expression of defence genes in these tissues. Expression of the ET/JA‐responsive PDF1.2 gene was markedly reduced in hrl1 npr1 and in SA‐depleted hrl1 nahG plants. In hrl1 nahG plants, expression of PDF1.2 was regulated by benzathiadiazole in a concentration‐dependent manner: induced at low concentration and suppressed at high concentration. The hrl1 etr1 plants lacked systemic PR‐1 expression, and exhibited compromised resistance to virulent Pseudomonas syringae and Peronospora parasitica. Inhibiting JA responses in hrl1 coi1 plants lead to exaggerated cell death and severe stunting of plants. Finally, the hrl1 mutation lead to elevated expression of AtrbohD, which encodes a major subunit of the NADPH oxidase complex. Our results indicate that defence gene expression and resistance against pathogens in hrl1 is regulated synergistically by SA and ET/JA defence pathways.