Characterisation of an Arabidopsis–Leptosphaeria maculans pathosystem: resistance partially requires camalexin biosynthesis and is independent of salicylic acid, ethylene and jasmonic acid signalling

• Published in: The Plant journal : for cell and molecular biology 2004-01, Vol.37 (1), p.9-20
• Main Authors: Bohman, Svante, Staal, Jens, Thomma, Bart P. H. J., Wang, Maolin, Dixelius, Christina
• Format: Article
• Language: English
• Subjects: alternaria-brassicicola; Arabidopsis - genetics; Arabidopsis - microbiology; Arabidopsis thaliana; Ascomycota - growth & development; Biological and medical sciences; blackleg; blackleg disease; brassica b-genome; Camalexin; causal agent; cell death; Copper Sulfate - pharmacology; coronatine; Cyclopentanes - metabolism; enhanced susceptibility; ethylene; Ethylenes - metabolism; fragment-length-polymorphism; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; Immunity, Innate - drug effects; Immunity, Innate - genetics; Indoles - metabolism; jasmonic acid; Leptosphaeria maculans; lms1 gene; molecular markers; Mutation; nahG gene; Oxylipins; Pathology, epidemiology, host-fungus relationships. Damages, economic importance; PDF1.2 gene; Peronospora parasitica; Phoma lingam; phytoalexin; phytoalexin-deficient mutants; Phytopathology. Animal pests. Plant and forest protection; plant defensin gene; Plant Diseases - microbiology; Plant Growth Regulators - metabolism; PR-1 gene; Salicylic Acid - metabolism; Signal Transduction - drug effects; Signal Transduction - genetics; Signal Transduction - physiology; Silver Nitrate - pharmacology; systemic acquired-resistance; Thiazoles - metabolism
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1046/j.1365-313X.2003.01927.x

Summary Out of 168 Arabidopsis accessions screened with isolates of Leptosphaeria maculans, one (An‐1) showed clear disease symptoms. In order to identify additional components involved in containment of L. maculans in Arabidopsis, a screen for L. maculans‐susceptible (lms) mutants was performed. Eleven lms mutants were isolated, which displayed differential susceptibility responses to L. maculans. lms1 was crossed with Columbia (Col‐0) and Ws‐0, and mapping data for both populations showed the highest linkage to a region on chromosome 2. Reduced levels of PR‐1 and PDF1.2 expression were found in lms1 compared to wild‐type plants 48 h after pathogen inoculation. In contrast, the lms1 mutant displayed upregulation of either marker gene upon chemical treatment, possibly as an effect of an altered ethylene (ET) response. To assess the contribution of different defence pathways, genotypes implicated in salicylic acid (SA) signalling plants expressing the bacterial salicylate hydroxylase (nahG) gene, non‐expressor of PR1 (npr1)‐1 and phytoalexin‐deficient (pad4‐1), jasmonic acid (JA) signalling (coronatine insensitive (coi)1‐16, enhanced disease susceptibility (eds)8‐1 and jasmonic acid resistant (jar)1‐1) and ET signalling (eds4‐1, ethylene insensitive (ein)2, ein3‐1 and ethylene resistant (etr)1‐1) were screened. All the genotypes screened were as resistant as wild‐type plants, demonstrating the dispensability of the pathways in L. maculans resistance. When mutants implicated in cell death responses were assayed, responsive to antagonist 1 (ran1)‐1 exhibited a weak susceptible phenotype, whereas accelerated cell death (acd)1‐20 showed a rapid lesion development. Camalexin is only partially responsible for L. maculans containment in Arabidopsis, as pad3‐1 and enhanced susceptibility to Alternaria (esa)1 clearly showed a susceptible response while wild‐type levels of camalexin were present in An‐1 and lms1. The data presented point to the existence of multiple defence mechanisms controlling the containment of L. maculans in Arabidopsis.