Of PAMPs and Effectors: The Blurred PTI-ETI Dichotomy

• Published in: The Plant cell Vol. 23; no. 1; pp. 4 - 15
• Main Authors: Thomma, Bart P.H.J, Nürnberger, Thorsten, Joosten, Matthieu H.A.J
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Biologists 2011
• Subjects: Bacteria - pathogenicity; Bacterial Proteins - immunology; Chitin; cultured rice cells; disease resistance gene; Fungal Proteins - immunology; Fungi - pathogenicity; fungus cladosporium-fulvum; high-affinity binding; Host-Pathogen Interactions; hypersensitive cell-death; innate immune-response; Microorganisms; Molecules; parasitica var.-nicotianae; pathogen pseudomonas-syringae; Pathogens; PERSPECTIVE; Plant cells; plant defense responses; Plant Diseases - immunology; Plant Diseases - microbiology; Plant Immunity; Plant Proteins - metabolism; Plant resistance; Plants; Plants - immunology; Plants - microbiology; receptor-like kinase; Receptors; Receptors, Pattern Recognition - metabolism; Rice; Virulence
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.110.082602

Typically, pathogen-associated molecular patterns (PAMPs) are considered to be conserved throughout classes of microbes and to contribute to general microbial fitness, whereas effectors are species, race, or strain specific and contribute to pathogen virulence. Both types of molecule can trigger plant immunity, designated PAMP-triggered and effector-triggered immunity (PTI and ETI, respectively). However, not all microbial defense activators conform to the common distinction between PAMPs and effectors. For example, some effectors display wide distribution, while some PAMPs are rather narrowly conserved or contribute to pathogen virulence. As effectors may elicit defense responses and PAMPs may be required for virulence, single components cannot exclusively be referred to by one of the two terms. Therefore, we put forward that the distinction between PAMPs and effectors, between PAMP receptors and resistance proteins, and, therefore, also between PTI and ETI, cannot strictly be maintained. Rather, as illustrated by examples provided here, there is a continuum between PTI and ETI. We argue that plant resistance is determined by immune receptors that recognize appropriate ligands to activate defense, the amplitude of which is likely determined by the level required for effective immunity.