Oomycete and fungal effector entry, a microbial Trojan horse

• Published in: New Phytologist Vol. 193; no. 4; pp. 874 - 881
• Main Author: Kale, Shiv D.
• Format: Journal Article Book Review
• Language: English
• Published: Oxford, UK New Phytologist Trust 01.03.2012; Blackwell Publishing Ltd; Wiley Subscription Services, Inc
• Subjects: Amino Acid Motifs; Amino Acid Sequence; Animal cells; Binding; Cell surface; Crops, Agricultural - microbiology; Defence mechanisms; Effector cells; Effectors; Endocytosis; Epithelial cells; Forest ecosystems; Fungal Proteins - metabolism; Fungi; Fungi - pathogenicity; Fungi - physiology; Host-Pathogen Interactions; Lipids; Machinery; Microorganisms; Minireviews; Molecular Sequence Data; mutualists; Oomycetes; Oomycetes - physiology; Parasite hosts; Pathogens; Phosphates; Phosphatidylinositol Phosphates - metabolism; Phospholipids; Phospholipids - metabolism; Plant cells; Plant Diseases - microbiology; Plants - microbiology; Proteins; RXLR and RXLR‐like; Secretion; Sequestering; Soybeans; Symbionts; Symbiosis; Translocation
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.2011.03968.x

Oomycete and fungal symbionts have significant impacts on most commercially important crop and forest species, and on natural ecosystems, both negatively as pathogens and positively as mutualists. Symbiosis may be facilitated through the secretion of effector proteins, some of which modulate a variety of host defense mechanisms. A subset of these secreted proteins are able to translocate into host cells. In the oomycete pathogens, two conserved Nterminal motifs, RXLR and dEER, mediate translocation of effector proteins into host cells independent of any pathogen-encoded machinery. An expanded ‘RXLR-like’ motif [R/K/H]✕[L/M I F/Y/W]X has been used to identify functional translocation motifs in hostcell-entering fungal effector proteins from pathogens and a mutualist. The RXLR-like translocation motifs were required for the fungal effectors to enter host cells in the absence of any pathogen-encoded machinery. Oomycete and fungal effectors with RXLR and RXLR-like motifs can bind phospholipids, specifically phosphatidylinositol-3-phosphate (PtdIns-3-P). Effector-PtdIns-3-P binding appears to mediate cell entry via lipid raft-mediated endocytosis, and could be blocked by sequestering cell surface PtdIns-3-P or by utilizing inositides that competitively inhibit effector binding to PtdIns-3-P. These findings suggest that effector blocking technologies could be developed and utilized in a variety of important crop species against a broad spectrum of plant pathogens.